MySQL 术语表MySQL Glossary

用于 ARCHIVE 表的元数据。与 .ARZ 文件 相对。具有此扩展名的文件总是包括在 MySQL 企业备份 产品的 mysqlbackup 命令生成的备份中。 Metadata for ARCHIVE tables. Contrast with .ARZ file. Files with this extension are always included in backups produced by the mysqlbackup command of the MySQL Enterprise Backup product.

另请参见 .ARZ 文件、MySQL 企业备份、mysqlbackup 命令。See Also .ARZ file, MySQL Enterprise Backup, mysqlbackup command.

ARCHIVE 表的数据。与 .ARM 文件 形成对比。具有此扩展名的文件总是包含在由 MySQL Enterprise Backup 产品的 mysqlbackup 命令生成的备份中。 Data for ARCHIVE tables. Contrast with .ARM file. Files with this extension are always included in backups produced by the mysqlbackup command of the MySQL Enterprise Backup product.

另请参见 .ARM 文件、MySQL Enterprise Backup、mysqlbackup 命令。See Also .ARM file, MySQL Enterprise Backup, mysqlbackup command.

一个缩写，代表原子性、一致性、隔离性和持久性。这些特性在数据库系统中都是理想的，并且都与事务的概念密切相关。InnoDB的事务特性遵循 ACID 原则。 An acronym standing for atomicity, consistency, isolation, and durability. These properties are all desirable in a database system, and are all closely tied to the notion of a transaction. The transactional features of InnoDB adhere to the ACID principles.

事务是可以被提交或回滚的原子工作单元。当一个事务对数据库进行多次更改时，要么在事务提交时所有更改都成功，要么在事务回滚时所有更改都被撤销。Transactions are atomic units of work that can be committed or rolled back. When a transaction makes multiple changes to the database, either all the changes succeed when the transaction is committed, or all the changes are undone when the transaction is rolled back.

数据库在任何时候都保持一致状态——在每次提交或回滚之后，以及在事务进行过程中。如果相关数据在多个表中被更新，查询看到的要么是所有旧值，要么是所有新值，而不是旧值和新值的混合。The database remains in a consistent state at all times — after each commit or rollback, and while transactions are in progress. If related data is being updated across multiple tables, queries see either all old values or all new values, not a mix of old and new values.

事务在进行时彼此之间受到保护（隔离）；它们不能相互干扰，也不能看到彼此未提交的数据。这种隔离是通过锁定机制实现的。经验丰富的用户可以调整隔离级别，以在确信事务确实不会互相干扰的情况下，以牺牲部分保护为代价换取更高的性能和并发性。Transactions are protected (isolated) from each other while they are in progress; they cannot interfere with each other or see each other's uncommitted data. This isolation is achieved through the locking mechanism. Experienced users can adjust the isolation level, trading off less protection in favor of increased performance and concurrency, when they can be sure that the transactions really do not interfere with each other.

事务的结果是持久的：一旦提交操作成功，该事务所做的更改就能免受断电、系统崩溃、竞争条件或其他许多非数据库应用可能面临的潜在危险的影响。持久性通常涉及写入磁盘存储，并具有一定程度的冗余，以防在写入操作期间出现断电或软件崩溃。（在InnoDB中，双写缓冲区有助于持久性。）The results of transactions are durable: once a commit operation succeeds, the changes made by that transaction are safe from power failures, system crashes, race conditions, or other potential dangers that many non-database applications are vulnerable to. Durability typically involves writing to disk storage, with a certain amount of redundancy to protect against power failures or software crashes during write operations. (In InnoDB, the doublewrite buffer assists with durability.)

另请参见 原子操作，提交，并发，双写缓存，隔离级别，锁定，回滚，事务。See Also atomic, commit, concurrency, doublewrite buffer, isolation level, locking, rollback, transaction.

An algorithm for InnoDB tables that smooths out the I/O overhead introduced by checkpoints. Instead of flushing all modified 预读 from the 缓冲池 to the data files at once, MySQL periodically flushes small sets of modified pages. The adaptive flushing algorithm extends this process by estimating the optimal rate to perform these periodic flushes, based on the rate of flushing and how fast redo information is generated. An algorithm for InnoDB tables that smooths out the I/O overhead introduced by checkpoints. Instead of flushing all modified pages from the buffer pool to the data files at once, MySQL periodically flushes small sets of modified pages. The adaptive flushing algorithm extends this process by estimating the optimal rate to perform these periodic flushes, based on the rate of flushing and how fast redo information is generated.

另请参见 缓冲池，检查点，数据文件，刷新，InnoDB，页面，重做日志。See Also buffer pool, checkpoint, data files, flush, InnoDB, page, redo log.

对 InnoDB 表的一种优化，可以通过在内存中构建 哈希索引 来加速使用 = 和 IN 运算符的查找。MySQL 监控 InnoDB 表的索引搜索，如果查询可以从哈希索引中受益，它会自动为频繁访问的索引 页 构建哈希索引。从某种意义上说，自适应哈希索引在运行时配置 MySQL 以利用充足的主内存，更接近主内存数据库的架构。此功能由 innodb_adaptive_hash_index 配置选项控制。因为此功能对某些工作负载有益，而对其他负载可能无效，并且哈希索引所使用的内存从 缓冲池 中预留，通常您应在启用和禁用此功能的情况下进行基准测试。 An optimization for InnoDB tables that can speed up lookups using = and IN operators, by constructing a hash index in memory. MySQL monitors index searches for InnoDB tables, and if queries could benefit from a hash index, it builds one automatically for index pages that are frequently accessed. In a sense, the adaptive hash index configures MySQL at runtime to take advantage of ample main memory, coming closer to the architecture of main-memory databases. This feature is controlled by the innodb_adaptive_hash_index configuration option. Because this feature benefits some workloads and not others, and the memory used for the hash index is reserved in the buffer pool, typically you should benchmark with this feature both enabled and disabled.

哈希索引总是基于表上现有的 B 树 索引构建的。MySQL 可以根据针对该索引的查询模式，在 B 树定义的键的任意长度前缀上构建哈希索引。哈希索引可以是部分的；整个 B 树索引不需要缓存在缓冲池中。The hash index is always built based on an existing B-tree index on the table. MySQL can build a hash index on a prefix of any length of the key defined for the B-tree, depending on the pattern of searches against the index. A hash index can be partial; the whole B-tree index does not need to be cached in the buffer pool.

另请参阅 B 树、缓冲池、哈希索引、页、辅助索引。See Also B-tree, buffer pool, hash index, page, secondary index.

一个用于使用 .NET 技术（如 ASP.NET）构建的应用程序的对象关系映射（ORM）框架。这样的应用程序可以通过 Connector/NET 组件与 MySQL 进行接口对接。 An object-relational mapping (ORM) framework for applications built using .NET technologies such as ASP.NET. Such applications can interface with MySQL through the Connector/NET component.

另请参阅 .NET、ASP.net、Connector/NET、Mono、Visual Studio。See Also .NET, ASP.net, Connector/NET, Mono, Visual Studio.

异步 I/O 的缩写。您可能会在 InnoDB 消息或关键字中看到此缩写。 Acronym for asynchronous I/O. You might see this acronym in InnoDB messages or keywords.

另请参见 异步 I/O。See Also asynchronous I/O.

在 ODBC 中，支持字符集和其他国际化方面的替代方法。与 Unicode 相比。Connector/ODBC 3.51 是 ANSI 驱动程序，而 Connector/ODBC 5.1 是 Unicode 驱动程序。 In ODBC, an alternative method of supporting character sets and other internationalization aspects. Contrast with Unicode. Connector/ODBC 3.51 is an ANSI driver, while Connector/ODBC 5.1 is a Unicode driver.

另请参见 Connector/ODBC，ODBC，Unicode。See Also Connector/ODBC, ODBC, Unicode.

API 提供从 客户端 程序对 MySQL 协议和 MySQL 资源的低级访问。与 连接器 提供的高级访问形成对比。 APIs provide low-level access to the MySQL protocol and MySQL resources from client programs. Contrast with the higher-level access provided by a Connector.

另请参见 C API、客户端、连接器、本地 C API、Perl API、PHP API、Python API、Ruby API。See Also C API, client, connector, native C API, Perl API, PHP API, Python API, Ruby API.

一组函数或过程。API 提供了一套稳定的名称和类型，用于函数、过程、参数和返回值。 A set of functions or procedures. An API provides a stable set of names and types for functions, procedures, parameters, and return values.

当由 MySQL 企业备份 产品生成的备份不包括备份进行期间发生的最新更改时，将备份文件更新以包含这些更改的过程称为 应用 步骤。它由 mysqlbackup 命令的 apply-log 选项指定。 When a backup produced by the MySQL Enterprise Backup product does not include the most recent changes that occurred while the backup was underway, the process of updating the backup files to include those changes is known as the apply step. It is specified by the apply-log option of the mysqlbackup command.

在应用更改之前，我们将这些文件称为 原始备份。在应用更改之后，我们将这些文件称为 已准备备份。这些更改记录在 ibbackup_logfile 文件中；一旦应用步骤完成，该文件就不再需要。Before the changes are applied, we refer to the files as a raw backup. After the changes are applied, we refer to the files as a prepared backup. The changes are recorded in the ibbackup_logfile file; once the apply step is finished, this file is no longer necessary.

另请参见 热备份、ibbackup_logfile、MySQL 企业备份、已准备备份、原始备份。See Also hot backup, ibbackup_logfile, MySQL Enterprise Backup, prepared backup, raw backup.

Kerberos 认证服务器。AS 也可以指认证服务器提供的认证服务。 A Kerberos authentication server. AS can also refer to the authentication service provided by an authentication server.

另请参见 认证服务器。See Also authentication server.

一个使用 .NET 技术和语言开发基于 Web 的应用程序的框架。这类应用程序可以通过 Connector/NET 组件与 MySQL 交互。 A framework for developing web-based applications using .NET technologies and languages. Such applications can interface with MySQL through the Connector/NET component.

另一种用于编写带有 MySQL 的服务器端网页的技术是 PHP。Another technology for writing server-side web pages with MySQL is PHP.

另请参见 .NET、ADO.NET、Connector/NET、Mono、PHP、Visual Studio。See Also .NET, ADO.NET, Connector/NET, Mono, PHP, Visual Studio.

在 .NET 系统中，通过 Connector/NET 访问的已编译代码库。存储在 GAC 中，以允许版本控制而不会发生命名冲突。 A library of compiled code in a .NET system, accessed through Connector/NET. Stored in the GAC to allow versioning without naming conflicts.

另请参见 .NET、GAC。See Also .NET, GAC.

一种允许在 I/O 完成之前继续进行其他处理的 I/O 操作类型。也称为 非阻塞 I/O，缩写为 AIO。InnoDB 对某些可以并行运行且不影响数据库可靠性的操作使用这种类型的 I/O，例如将尚未实际请求但可能很快需要的页面读取到 缓冲池 中。 A type of I/O operation that allows other processing to proceed before the I/O is completed. Also known as nonblocking I/O and abbreviated as AIO. InnoDB uses this type of I/O for certain operations that can run in parallel without affecting the reliability of the database, such as reading pages into the buffer pool that have not actually been requested, but might be needed soon.

历史上，InnoDB 仅在 Windows 系统上使用异步 I/O。从 InnoDB 插件 1.1 和 MySQL 5.5 开始，InnoDB 在 Linux 系统上也使用异步 I/O。此更改引入了对 libaio 的依赖。在 Linux 系统上，异步 I/O 通过 innodb_use_native_aio 选项进行配置，该选项默认启用。在其他类似 Unix 的系统上，InnoDB 仅使用同步 I/O。Historically, InnoDB used asynchronous I/O on Windows systems only. Starting with the InnoDB Plugin 1.1 and MySQL 5.5, InnoDB uses asynchronous I/O on Linux systems. This change introduces a dependency on libaio. Asynchronous I/O on Linux systems is configured using the innodb_use_native_aio option, which is enabled by default. On other Unix-like systems, InnoDB uses synchronous I/O only.

另请参阅 缓冲池，非阻塞 I/O。See Also buffer pool, nonblocking I/O.

在 SQL 环境中，事务 是工作单元，它要么完全成功（当 提交 时），要么完全无效（当 回滚 时）。事务的不可分割（“原子”）特性是缩写 ACID 中的 “A”。 In the SQL context, transactions are units of work that either succeed entirely (when committed) or have no effect at all (when rolled back). The indivisible ("atomic") property of transactions is the “A” in the acronym ACID.

另见 ACID、提交、回滚、事务。See Also ACID, commit, rollback, transaction.

原子 DDL 语句是将与 DDL 操作相关的 数据字典 更新、存储引擎 操作和 二进制日志 写入组合成单一的、原子的事务。该事务要么完全提交，要么回滚，即使服务器在操作过程中停止。MySQL 8.0 添加了对原子 DDL 的支持。有关更多信息，请参见 第 15.1.1 节，“原子数据定义语句支持”。 An atomic DDL statement is one that combines the data dictionary updates, storage engine operations, and binary log writes associated with a DDL operation into a single, atomic transaction. The transaction is either fully committed or rolled back, even if the server halts during the operation. Atomic DDL support was added in MySQL 8.0. For more information, see Section 15.1.1, “Atomic Data Definition Statement Support”.

另请参见 二进制日志、数据字典、DDL、存储引擎。See Also binary log, data dictionary, DDL, storage engine.

CPU 提供的特殊指令，用于确保关键的低级操作不会被中断。 Special instructions provided by the CPU, to ensure that critical low-level operations cannot be interrupted.

在 Kerberos 中，一种服务提供初始票据，该票据用于获取票据授权票 (TGT)，从而可以从票据授权服务器 (TGS) 获取其他票据。认证服务器 (AS) 与 TGS 结合组成密钥分发中心 (KDC)。 In Kerberos, a service that provides the initial ticket needed to obtain a ticket-granting ticket (TGT) that is needed to obtain other tickets from the ticket-granting server (TGS). The authentication server (AS) combined with a TGS make up a key distribution center (KDC).

另请参见 密钥分发中心, 票据授权服务器。See Also key distribution center, ticket-granting server.

表列的一种属性（由 AUTO_INCREMENT 关键字指定），自动在该列中添加递增的数值序列。 A property of a table column (specified by the AUTO_INCREMENT keyword) that automatically adds an ascending sequence of values in the column.

它为开发者节省了工作量，不必在插入新行时产生新的唯一值。它为查询优化器提供了有用的信息，因为该列已知不为空且具有唯一值。这样的列的值可以在各种情况下用作查找键，并且由于它们是自动生成的，没有理由去更改它们；因此，主键列通常被指定为自增列。It saves work for the developer, not to have to produce new unique values when inserting new rows. It provides useful information for the query optimizer, because the column is known to be not null and with unique values. The values from such a column can be used as lookup keys in various contexts, and because they are auto-generated there is no reason to ever change them; for this reason, primary key columns are often specified as auto-incrementing.

自增列在基于语句的复制中可能会出现问题，因为在副本上重放这些语句可能不会产生与源端相同的一组列值，这主要是由于时间问题。当您有一个自增主键时，只能在设置 innodb_autoinc_lock_mode=1 的情况下使用基于语句的复制。如果您使用 innodb_autoinc_lock_mode=2，它允许插入操作具有更高的并发性，请使用 基于行的复制 而不是 基于语句的复制。设置 innodb_autoinc_lock_mode=0 除了为了兼容性之外，不应该使用。Auto-increment columns can be problematic with statement-based replication, because replaying the statements on a replica might not produce the same set of column values as on the source, due to timing issues. When you have an auto-incrementing primary key, you can use statement-based replication only with the setting innodb_autoinc_lock_mode=1. If you have innodb_autoinc_lock_mode=2, which allows higher concurrency for insert operations, use row-based replication rather than statement-based replication. The setting innodb_autoinc_lock_mode=0 should not be used except for compatibility purposes.

连续锁模式 (innodb_autoinc_lock_mode=1) 是 MySQL 8.0.3 之前的默认设置。从 MySQL 8.0.3 开始，交错锁模式 (innodb_autoinc_lock_mode=2) 成为默认设置，这反映了默认复制类型从基于语句的复制变为基于行的复制的变化。Consecutive lock mode (innodb_autoinc_lock_mode=1) is the default setting prior to MySQL 8.0.3. As of MySQL 8.0.3, interleaved lock mode (innodb_autoinc_lock_mode=2) is the default, which reflects the change from statement-based to row-based replication as the default replication type.

另请参见 自增锁定、innodb_autoinc_lock_mode、主键、基于行的复制、基于语句的复制。See Also auto-increment locking, innodb_autoinc_lock_mode, primary key, row-based replication, statement-based replication.

自增主键的便利性伴随着一些并发性的权衡。在最简单的情况下，如果一个事务正在向表中插入值，其他事务必须等待才能进行自己的插入操作，以便第一个事务插入的行能够获得连续的主键值。InnoDB 包含优化方法和 innodb_autoinc_lock_mode 选项，允许你在可预测的自增值序列和插入操作的最大并发之间配置最佳平衡。 The convenience of an auto-increment primary key involves some tradeoff with concurrency. In the simplest case, if one transaction is inserting values into the table, any other transactions must wait to do their own inserts into that table, so that rows inserted by the first transaction receive consecutive primary key values. InnoDB includes optimizations and the innodb_autoinc_lock_mode option so that you can configure and optimal balance between predictable sequences of auto-increment values and maximum concurrency for insert operations.

参见 自动递增、并发、innodb_autoinc_lock_mode。See Also auto-increment, concurrency, innodb_autoinc_lock_mode.

这个设置会在每条 SQL 语句后执行一次 提交 操作。对于跨多条语句的 InnoDB 表的 事务，不推荐使用这种模式。它可以提升 InnoDB 表的 只读事务 的性能，因为它最小化了 锁定 和 撤销 数据的生成开销，尤其是在 MySQL 5.6.4 及更高版本中。对于处理 MyISAM 表（事务不适用）也是合适的。 A setting that causes a commit operation after each SQL statement. This mode is not recommended for working with InnoDB tables with transactions that span several statements. It can help performance for read-only transactions on InnoDB tables, where it minimizes overhead from locking and generation of undo data, especially in MySQL 5.6.4 and up. It is also appropriate for working with MyISAM tables, where transactions are not applicable.

另请参见 提交、锁定、只读事务、SQL、事务、撤销。See Also commit, locking, read-only transaction, SQL, transaction, undo.

在主机上处理故障的能力，如果必要，还能从 MySQL、操作系统或硬件的故障及可能导致停机的维护活动中恢复。通常与 可扩展性 配对，作为大规模部署的关键方面。 The ability to cope with, and if necessary recover from, failures on the host, including failures of MySQL, the operating system, or the hardware and maintenance activity that may otherwise cause downtime. Often paired with scalability as critical aspects of a large-scale deployment.

另请参见 可扩展性。See Also scalability.

一款带许可的产品，可对 MySQL 数据库执行 热备份。在备份 InnoDB 表时，它提供了最高的效率和灵活性，但也可以备份 MyISAM 及其他类型的表。 A licensed product that performs hot backups of MySQL databases. It offers the most efficiency and flexibility when backing up InnoDB tables, but can also back up MyISAM and other kinds of tables.

另请参见 热备份，InnoDB。See Also hot backup, InnoDB.

一种在数据库索引中广泛使用的树形数据结构。该结构始终保持排序状态，从而可以快速查找精确匹配（等于运算符）和范围（例如，大于、小于，以及 BETWEEN 运算符）的数据。这种类型的索引在大多数存储引擎中都可用，例如 InnoDB 和 MyISAM。 A tree data structure that is popular for use in database indexes. The structure is kept sorted at all times, enabling fast lookup for exact matches (equals operator) and ranges (for example, greater than, less than, and BETWEEN operators). This type of index is available for most storage engines, such as InnoDB and MyISAM.

由于 B 树节点可以有多个子节点，因此 B 树不同于每个节点仅限 2 个子节点的二叉树。Because B-tree nodes can have many children, a B-tree is not the same as a binary tree, which is limited to 2 children per node.

与 哈希索引 相比，哈希索引仅在 MEMORY 存储引擎中可用。MEMORY 存储引擎也可以使用 B 树索引，如果某些查询使用范围操作符，则应为 MEMORY 表选择 B 树索引。Contrast with hash index, which is only available in the MEMORY storage engine. The MEMORY storage engine can also use B-tree indexes, and you should choose B-tree indexes for MEMORY tables if some queries use range operators.

使用术语 B 树旨在指代一般的索引设计类别。MySQL 存储引擎使用的 B 树结构可以视为由于某些在经典 B 树设计中不存在的复杂性而产生的变体。有关相关信息，请参阅 InnoDB 页面结构 Fil Header 部分的 MySQL 内部手册。The use of the term B-tree is intended as a reference to the general class of index design. B-tree structures used by MySQL storage engines may be regarded as variants due to sophistications not present in a classic B-tree design. For related information, refer to the InnoDB Page Structure Fil Header section of the MySQL Internals Manual.

另请参见 哈希索引。See Also hash index.

如果标识符包含特殊字符或保留字，则 MySQL SQL 语句中的标识符必须使用反引号字符 (`) 引起来。例如，要引用名为 FOO#BAR 的表或名为 SELECT 的列，你需要将标识符指定为 `FOO#BAR` 和 `SELECT`。由于反引号提供了额外的安全性，它们在程序生成的 SQL 语句中被广泛使用，因为此类标识符名称可能事先未知。 Identifiers within MySQL SQL statements must be quoted using the backtick character (`) if they contain special characters or reserved words. For example, to refer to a table named FOO#BAR or a column named SELECT, you would specify the identifiers as `FOO#BAR` and `SELECT`. Since the backticks provide an extra level of safety, they are used extensively in program-generated SQL statements, where the identifier names might not be known in advance.

许多其他数据库系统在这种特殊名称周围使用双引号 (")。为了可移植性，你可以在 MySQL 中启用 ANSI_QUOTES 模式，并使用双引号代替反引号来限定标识符名称。Many other database systems use double quotation marks (") around such special names. For portability, you can enable ANSI_QUOTES mode in MySQL and use double quotation marks instead of backticks to qualify identifier names.

另请参见 SQL。See Also SQL.

从 MySQL 实例中复制部分或全部表数据和元数据以进行保存的过程。也可以指复制文件的集合。这是 DBA 的一项关键任务。此过程的逆操作是 恢复 操作。 The process of copying some or all table data and metadata from a MySQL instance, for safekeeping. Can also refer to the set of copied files. This is a crucial task for DBAs. The reverse of this process is the restore operation.

在 MySQL 中，物理备份 由 MySQL Enterprise Backup 产品执行，而 逻辑备份 由 mysqldump 命令执行。这些技术在备份数据的大小、表示形式以及速度（尤其是恢复操作的速度）方面具有不同的特性。With MySQL, physical backups are performed by the MySQL Enterprise Backup product, and logical backups are performed by the mysqldump command. These techniques have different characteristics in terms of size and representation of the backup data, and speed (especially speed of the restore operation).

备份根据其对正常数据库操作的干扰程度进一步分类为热备份、温备份或冷备份。（热备份干扰最小，冷备份干扰最大。）Backups are further classified as hot, warm, or cold depending on how much they interfere with normal database operation. (Hot backups have the least interference, cold backups the most.)

另请参见 冷备份、热备份、逻辑备份、MySQL 企业备份、mysqldump、物理备份、温备份。See Also cold backup, hot backup, logical backup, MySQL Enterprise Backup, mysqldump, physical backup, warm backup.

一个非生成的表列，用于作为存储生成列或虚拟生成列的基础。换句话说，基础列是生成列定义的一部分的非生成表列。 A non-generated table column upon which a stored generated column or virtual generated column is based. In other words, a base column is a non-generated table column that is part of a generated column definition.

另请参见 生成列，存储生成列，虚拟生成列。See Also generated column, stored generated column, virtual generated column.

软件产品生命周期的早期阶段，此时软件仅可用于评估，通常没有明确的发行版本号或版本号小于 1。InnoDB 不使用 beta 版本标记，而是更倾向于一个可持续数个小版本发布阶段的早期采用者阶段，最终发布为GA版本。 An early stage in the life of a software product, when it is available only for evaluation, typically without a definite release number or a number less than 1. InnoDB does not use the beta designation, preferring an early adopter phase that can extend over several point releases, leading to a GA release.

另请参见 早期采用者、GA。See Also early adopter, GA.

一个包含尝试更改表数据的所有语句或行更改记录的文件。二进制日志的内容可以重放，以便在复制场景中使副本保持最新，或者在从备份恢复表数据后使数据库保持最新。二进制日志功能可以开启或关闭，但如果使用复制或执行备份，Oracle 建议始终启用该功能。 A file containing a record of all statements or row changes that attempt to change table data. The contents of the binary log can be replayed to bring replicas up to date in a replication scenario, or to bring a database up to date after restoring table data from a backup. The binary logging feature can be turned on and off, although Oracle recommends always enabling it if you use replication or perform backups.

您可以使用 mysqlbinlog 命令来检查二进制日志的内容，或在复制或恢复期间重放它。有关二进制日志的完整信息，请参见 第 7.4.4 节，“二进制日志”。有关 MySQL 配置选项与二进制日志相关的信息，请参见 第 19.1.6.4 节，“二进制日志选项和变量”。You can examine the contents of the binary log, or replay it during replication or recovery, by using the mysqlbinlog command. For full information about the binary log, see Section 7.4.4, “The Binary Log”. For MySQL configuration options related to the binary log, see Section 19.1.6.4, “Binary Logging Options and Variables”.

对于 MySQL 企业备份 产品，二进制日志的文件名以及文件中的当前位置是重要的详细信息。在复制环境中进行备份时，为记录源的信息，可以指定 --slave-info 选项。For the MySQL Enterprise Backup product, the file name of the binary log and the current position within the file are important details. To record this information for the source when taking a backup in a replication context, you can specify the --slave-info option.

在 MySQL 5.0 之前，类似的功能被称为更新日志。在 MySQL 5.0 及更高版本中，二进制日志取代了更新日志。Prior to MySQL 5.0, a similar capability was available, known as the update log. In MySQL 5.0 and higher, the binary log replaces the update log.

另请参阅 binlog、MySQL 企业备份、复制。See Also binlog, MySQL Enterprise Backup, replication.

二进制日志 文件的非正式名称。例如，你可能会在电子邮件或论坛讨论中看到这个缩写的使用。 An informal name for the binary log file. For example, you might see this abbreviation used in e-mail messages or forum discussions.

另请参见 二进制日志。See Also binary log.

由 WITH QUERY EXPANSION 子句启用的一种特殊模式的 全文搜索。它执行两次搜索，其中第二次搜索的搜索短语是由第一次搜索中最相关的几份文档与原始搜索短语组合而成的。该技术主要适用于短搜索短语，可能只是一个单词。它可以发现那些文档中未出现精确搜索词的相关匹配项。 A special mode of full-text search enabled by the WITH QUERY EXPANSION clause. It performs the search twice, where the search phrase for the second search is the original search phrase concatenated with the few most highly relevant documents from the first search. This technique is mainly applicable for short search phrases, perhaps only a single word. It can uncover relevant matches where the precise search term does not occur in the document.

另请参见 全文搜索。See Also full-text search.

SQL 数据类型（TINYBLOB、BLOB、MEDIUMBLOB 和 LONGBLOB）用于包含任意大小的二进制数据的对象。用于存储文档、图像、音频文件以及其他无法轻易分解为 MySQL 表中行和列的信息。在 MySQL 应用程序中处理 BLOB 的技术因各个 连接器 和 API 而异。MySQL Connector/ODBC 将 BLOB 值定义为 LONGVARBINARY。对于大规模、自由格式的字符数据集合，业界术语是 CLOB，在 MySQL 中由 TEXT 数据类型表示。 An SQL data type (TINYBLOB, BLOB, MEDIUMBLOB, and LONGBLOB) for objects containing any kind of binary data, of arbitrary size. Used for storing documents, images, sound files, and other kinds of information that cannot easily be decomposed to rows and columns within a MySQL table. The techniques for handling BLOBs within a MySQL application vary with each Connector and API. MySQL Connector/ODBC defines BLOB values as LONGVARBINARY. For large, free-form collections of character data, the industry term is CLOB, represented by the MySQL TEXT data types.

另请参阅 API，CLOB，连接器，Connector/ODBC。See Also API, CLOB, connector, Connector/ODBC.

系统中受大小或容量限制的一部分，其效果是限制整体吞吐量。例如，内存区域可能比所需的小；访问单个必需资源可能会阻止多个 CPU 核心同时运行；或者等待磁盘 I/O 完成可能会阻止 CPU 以全容量运行。消除瓶颈往往能提高 并发性。例如，拥有多个 InnoDB 缓冲池 实例可以在多个会话同时从缓冲池读取和写入时减少争用。 A portion of a system that is constrained in size or capacity, that has the effect of limiting overall throughput. For example, a memory area might be smaller than necessary; access to a single required resource might prevent multiple CPU cores from running simultaneously; or waiting for disk I/O to complete might prevent the CPU from running at full capacity. Removing bottlenecks tends to improve concurrency. For example, the ability to have multiple InnoDB buffer pool instances reduces contention when multiple sessions read from and write to the buffer pool simultaneously.

另请参见 缓冲池，并发性。See Also buffer pool, concurrency.

一次 关闭 操作紧接着立即进行重启。理想情况下，预热 时间相对较短，以便性能和吞吐量能够快速恢复到较高水平。 A shutdown operation immediately followed by a restart. Ideally with a relatively short warmup period so that performance and throughput quickly return to a high level.

另请参见 关闭。See Also shutdown.

用于管理 InnoDB 缓冲池 中不同大小 页 的机制。 A mechanism for managing different-sized pages in the InnoDB buffer pool.

另请参见 缓冲池、页、页大小。See Also buffer pool, page, page size.

用于临时存储的内存或磁盘区域。数据会缓存在内存中，以便通过少量的大型 I/O 操作而非大量小型操作高效地写入磁盘。数据也会缓存在磁盘上以提高可靠性，这样即使在最糟糕的时间发生 崩溃 或其他故障时，也能够恢复。InnoDB 使用的主要缓冲类型是 缓冲池、双写缓冲 和 更改缓冲。 A memory or disk area used for temporary storage. Data is buffered in memory so that it can be written to disk efficiently, with a few large I/O operations rather than many small ones. Data is buffered on disk for greater reliability, so that it can be recovered even when a crash or other failure occurs at the worst possible time. The main types of buffers used by InnoDB are the buffer pool, the doublewrite buffer, and the change buffer.

另请参见 缓冲池、更改缓冲区、崩溃、双写缓冲区。See Also buffer pool, change buffer, crash, doublewrite buffer.

存储缓存 InnoDB 数据（包括表和索引）的内存区域。为了高吞吐量读操作的效率，缓冲池被划分为可以容纳多行的 页。为了缓存管理的效率，缓冲池实现为页的链表；很少使用的数据会使用一种 LRU 算法的变体从缓存中逐出。在内存较大的系统中，你可以通过将缓冲池划分为多个 缓冲池实例 来提高并发性。 The memory area that holds cached InnoDB data for both tables and indexes. For efficiency of high-volume read operations, the buffer pool is divided into pages that can potentially hold multiple rows. For efficiency of cache management, the buffer pool is implemented as a linked list of pages; data that is rarely used is aged out of the cache, using a variation of the LRU algorithm. On systems with large memory, you can improve concurrency by dividing the buffer pool into multiple buffer pool instances.

一些 InnoDB 状态变量、INFORMATION_SCHEMA 表和 performance_schema 表有助于监控缓冲池的内部运作。从 MySQL 5.6 开始，您可以通过在服务器关闭时保存缓冲池状态，并在服务器启动时将缓冲池恢复到相同状态，来避免服务器重启后的长时间预热，尤其适用于具有大缓冲池的实例。请参阅 第 17.8.3.6 节，“保存和恢复缓冲池状态”。Several InnoDB status variables, INFORMATION_SCHEMA tables, and performance_schema tables help to monitor the internal workings of the buffer pool. Starting in MySQL 5.6, you can avoid a lengthy warmup period after restarting the server, particularly for instances with large buffer pools, by saving the buffer pool state at server shutdown and restoring the buffer pool to the same state at server startup. See Section 17.8.3.6, “Saving and Restoring the Buffer Pool State”.

另请参见 缓冲池实例，LRU，页，预热。See Also buffer pool instance, LRU, page, warm up.

缓冲池 可以被划分为的多个区域中的任意一个，由 innodb_buffer_pool_instances 配置选项控制。innodb_buffer_pool_size 指定的总内存大小将在所有缓冲池实例中进行分配。通常，对于向 InnoDB 缓冲池分配多个 GB 的系统，多个缓冲池实例是合适的，每个实例大小为 1GB 或更大。在从许多并发会话加载或查找缓冲池中大量数据的系统上，多个缓冲池实例可以减少对管理缓冲池的数据结构的独占访问的争用。 Any of the multiple regions into which the buffer pool can be divided, controlled by the innodb_buffer_pool_instances configuration option. The total memory size specified by innodb_buffer_pool_size is divided among all buffer pool instances. Typically, having multiple buffer pool instances is appropriate for systems that allocate multiple gigabytes to the InnoDB buffer pool, with each instance being one gigabyte or larger. On systems loading or looking up large amounts of data in the buffer pool from many concurrent sessions, having multiple buffer pool instances reduces contention for exclusive access to data structures that manage the buffer pool.

另见 缓冲池。See Also buffer pool.

MySQL 中的内置 InnoDB 存储引擎是该存储引擎的原始发行形式。与 InnoDB 插件 相对。自 MySQL 5.5 起，InnoDB 插件重新合并回 MySQL 代码库作为内置 InnoDB 存储引擎（称为 InnoDB 1.1）。 The built-in InnoDB storage engine within MySQL is the original form of distribution for the storage engine. Contrast with the InnoDB Plugin. Starting with MySQL 5.5, the InnoDB Plugin is merged back into the MySQL code base as the built-in InnoDB storage engine (known as InnoDB 1.1).

这个区别主要在 MySQL 5.1 中很重要，因为某个特性或错误修复可能适用于 InnoDB 插件，但不适用于内置 InnoDB，反之亦然。This distinction is important mainly in MySQL 5.1, where a feature or bug fix might apply to the InnoDB Plugin but not the built-in InnoDB, or vice versa.

另见 InnoDB。See Also InnoDB.

构成业务软件基础的关系和操作序列，用于运营商业公司。有时这些规则由法律规定，有时则由公司政策决定。通过仔细的规划，可以确保数据库中编码和执行的关系，以及通过应用逻辑执行的操作，准确反映公司的真实政策，并能够应对现实中的情况。 The relationships and sequences of actions that form the basis of business software, used to run a commercial company. Sometimes these rules are dictated by law, other times by company policy. Careful planning ensures that the relationships encoded and enforced by the database, and the actions performed through application logic, accurately reflect the real policies of the company and can handle real-life situations.

例如，员工离开公司可能会触发人力资源部门的一系列操作。人力资源数据库可能还需要具有灵活性，以表示已经被聘用但尚未开始工作的人员信息。关闭在线服务账户可能会导致数据库中的数据被删除，或者数据可能被移动或标记，以便在账户重新开启时可以恢复。一家公司可能会制定关于工资最高限额、最低限额和调整的政策，除此之外还会有基本的合理性检查，例如工资不能为负数。零售数据库可能不允许同一序列号的商品被退货超过一次，或者不允许超过某个数额的信用卡购买，而用于检测欺诈的数据库可能允许这些情况。For example, an employee leaving a company might trigger a sequence of actions from the human resources department. The human resources database might also need the flexibility to represent data about a person who has been hired, but not yet started work. Closing an account at an online service might result in data being removed from a database, or the data might be moved or flagged so that it could be recovered if the account is re-opened. A company might establish policies regarding salary maximums, minimums, and adjustments, in addition to basic sanity checks such as the salary not being a negative number. A retail database might not allow a purchase with the same serial number to be returned more than once, or might not allow credit card purchases above a certain value, while a database used to detect fraud might allow these kinds of things.

另请参见 关系型。See Also relational.

与 InnoDB 可迁移表空间 功能一起使用的元数据文件。它由命令 FLUSH TABLES ... FOR EXPORT 生成，将一个或多个表置于一致状态，从而可以复制到另一台服务器。.cfg 文件会与对应的 .ibd 文件 一起复制，并在 ALTER TABLE ... IMPORT TABLESPACE 步骤中用于调整 .ibd 文件的内部值，例如 空间 ID。 A metadata file used with the InnoDB transportable tablespace feature. It is produced by the command FLUSH TABLES ... FOR EXPORT, puts one or more tables in a consistent state that can be copied to another server. The .cfg file is copied along with the corresponding .ibd file, and used to adjust the internal values of the .ibd file, such as the space ID, during the ALTER TABLE ... IMPORT TABLESPACE step.

另请参见 .ibd 文件，空间 ID，可传输表空间。See Also .ibd file, space ID, transportable tablespace.

一种结合了可移植性、性能以及对低级硬件功能访问的编程语言，使其成为编写操作系统、驱动程序和其他类型系统软件的流行选择。许多复杂的应用程序、语言和可重用模块包含用 C 编写的部分，并与用其他语言编写的高级组件结合在一起。其核心语法对 C 、Java 和 C# 开发者来说很熟悉。 A programming language that combines portability with performance and access to low-level hardware features, making it a popular choice for writing operating systems, drivers, and other kinds of system software. Many complex applications, languages, and reusable modules feature pieces written in C, tied together with high-level components written in other languages. Its core syntax is familiar to C++, Java, and C# developers.

另请参见 C API，C，C#，Java。See Also C API, C++, C#, Java.

C API 代码随 MySQL 一起分发。它包含在 libmysqlclient 库中，使 C 程序能够访问数据库。 The C API code is distributed with MySQL. It is included in the libmysqlclient library and enables C programs to access a database.

另请参见 API，C，libmysqlclient。See Also API, C, libmysqlclient.

一种结合了强类型和面向对象特性的编程语言，在 Microsoft .NET 框架或其开源版本 Mono 上运行。通常用于使用 ASP.net 框架创建应用程序。其语法对于 C、C++ 和 Java 开发者来说很熟悉。 A programming language combining strong typing and object-oriented features, running within the Microsoft .NET framework or its open-source counterpart Mono. Often used for creating applications with the ASP.net framework. Its syntax is familiar to C, C++ and Java developers.

另请参见 .NET、ASP.net、C、Connector/NET、C++、Java、Mono。See Also .NET, ASP.net, C, Connector/NET, C++, Java, Mono.

一种其核心语法对 C 开发者来说非常熟悉的编程语言。提供对低级操作的访问以提升性能，同时结合了更高级的数据类型、面向对象特性和垃圾回收。若要为 MySQL 编写 C 应用程序，您需要使用 Connector/C 组件。 A programming language with core syntax familiar to C developers. Provides access to low-level operations for performance, combined with higher-level data types, object-oriented features, and garbage collection. To write C++ applications for MySQL, you use the Connector/C++ component.

另见 C，Connector/C 。See Also C, Connector/C++.

泛指用于存储数据副本以便频繁或高速检索的任何内存区域。在 InnoDB 中，主要的缓存结构类型是 缓冲池。 The general term for any memory area that stores copies of data for frequent or high-speed retrieval. In InnoDB, the primary kind of cache structure is the buffer pool.

另请参见 缓冲区，缓冲池。See Also buffer, buffer pool.

表中某个 列 中不同值的数量。当查询引用具有关联 索引 的列时，每列的基数会影响哪种访问方法最有效。例如，对于具有 唯一约束 的列，不同值的数量等于表中的行数。如果一个表有一百万行，但某一列只有 10 个不同的值，每个值平均出现 100,000 次。像 SELECT c1 FROM t1 WHERE c1 = 50; 这样的查询可能返回 1 行或大量行，并且数据库服务器可能会根据 c1 的基数以不同的方式处理查询。 The number of different values in a table column. When queries refer to columns that have an associated index, the cardinality of each column influences which access method is most efficient. For example, for a column with a unique constraint, the number of different values is equal to the number of rows in the table. If a table has a million rows but only 10 different values for a particular column, each value occurs (on average) 100,000 times. A query such as SELECT c1 FROM t1 WHERE c1 = 50; thus might return 1 row or a huge number of rows, and the database server might process the query differently depending on the cardinality of c1.

如果一列中的值分布非常不均匀，基数可能不是确定最佳查询计划的好方法。例如，SELECT c1 FROM t1 WHERE c1 = x; 当 x=50 时可能返回 1 行，而当 x=30 时可能返回一百万行。在这种情况下，你可能需要使用 索引提示 来提供关于哪种查找方法对特定查询更有效的建议。If the values in a column have a very uneven distribution, the cardinality might not be a good way to determine the best query plan. For example, SELECT c1 FROM t1 WHERE c1 = x; might return 1 row when x=50 and a million rows when x=30. In such a case, you might need to use index hints to pass along advice about which lookup method is more efficient for a particular query.

基数也可以应用于多列中存在的不同值的数量，例如在 复合索引 中。Cardinality can also apply to the number of distinct values present in multiple columns, as in a composite index.

另请参见 列，复合索引，索引，索引提示，持久统计，随机深入，选择性，唯一约束。See Also column, composite index, index, index hint, persistent statistics, random dive, selectivity, unique constraint.

一种特殊的数据结构，用于记录在二级索引中的页面所发生的更改。这些值可能来源于 SQL INSERT、UPDATE或DELETE 语句（DML）。涉及更改缓冲区的一系列特性统称为更改缓冲，包括插入缓冲、删除缓冲和清理缓冲。 A special data structure that records changes to pages in secondary indexes. These values could result from SQL INSERT, UPDATE, or DELETE statements (DML). The set of features involving the change buffer is known collectively as change buffering, consisting of insert buffering, delete buffering, and purge buffering.

当来自二级索引的相关页面不在缓冲池中时，变更才会记录在变更缓冲区中。当相关的索引页面在关联的变更仍在变更缓冲区中时被加载到缓冲池中，该页面的变更会在缓冲池中应用（合并），使用变更缓冲区中的数据。系统大部分时间空闲或在缓慢关机期间运行的清理操作会定期将新的索引页面写入磁盘。与每个值立即写入磁盘相比，清理操作可以更高效地写入一系列索引值对应的磁盘块。Changes are only recorded in the change buffer when the relevant page from the secondary index is not in the buffer pool. When the relevant index page is brought into the buffer pool while associated changes are still in the change buffer, the changes for that page are applied in the buffer pool (merged) using the data from the change buffer. Periodically, the purge operation that runs during times when the system is mostly idle, or during a slow shutdown, writes the new index pages to disk. The purge operation can write the disk blocks for a series of index values more efficiently than if each value were written to disk immediately.

在物理上，变更缓冲区是系统表空间的一部分，因此索引更改在数据库重启后仍然保持缓冲状态。只有当页面由于某些其他读取操作被加载到缓冲池时，这些更改才会被应用（合并）。Physically, the change buffer is part of the system tablespace, so that the index changes remain buffered across database restarts. The changes are only applied (merged) when the pages are brought into the buffer pool due to some other read operation.

存储在变更缓冲区中的数据类型和数量由innodb_change_buffering和innodb_change_buffer_max_size配置选项控制。要查看变更缓冲区中当前数据的信息，请执行SHOW ENGINE INNODB STATUS命令。The kinds and amount of data stored in the change buffer are governed by the innodb_change_buffering and innodb_change_buffer_max_size configuration options. To see information about the current data in the change buffer, issue the SHOW ENGINE INNODB STATUS command.

以前被称为 插入缓冲区。Formerly known as the insert buffer.

另请参见 缓冲池，更改缓冲，删除缓冲，DML，插入缓冲，插入缓冲处理，合并，页，清除，清除缓冲处理，二级索引，系统表空间。See Also buffer pool, change buffering, delete buffering, DML, insert buffer, insert buffering, merge, page, purge, purge buffering, secondary index, system tablespace.

涉及 更改缓冲区 的功能的一般术语，包括 插入缓冲、删除缓冲 和 清除缓冲。由 SQL 语句引起的索引更改，通常可能涉及随机 I/O 操作，会被暂时保留，并由后台 线程 定期执行。这一操作序列能够比每个值立即写入磁盘更高效地写入一系列索引值的磁盘块。由 innodb_change_buffering 和 innodb_change_buffer_max_size 配置选项控制。 The general term for the features involving the change buffer, consisting of insert buffering, delete buffering, and purge buffering. Index changes resulting from SQL statements, which could normally involve random I/O operations, are held back and performed periodically by a background thread. This sequence of operations can write the disk blocks for a series of index values more efficiently than if each value were written to disk immediately. Controlled by the innodb_change_buffering and innodb_change_buffer_max_size configuration options.

另请参见 更改缓冲区、删除缓冲、插入缓冲、清除缓冲。See Also change buffer, delete buffering, insert buffering, purge buffering.

当对缓存于 缓冲池 中的数据页进行修改时，这些修改会在稍后写入 数据文件，这一过程称为 刷新。检查点是已成功写入数据文件的最新修改记录（以 LSN 值表示）。 As changes are made to data pages that are cached in the buffer pool, those changes are written to the data files sometime later, a process known as flushing. The checkpoint is a record of the latest changes (represented by an LSN value) that have been successfully written to the data files.

参见 缓冲池、数据文件、刷新、模糊检查点、LSN。See Also buffer pool, data files, flush, fuzzy checkpointing, LSN.

在 InnoDB 中，当 表空间 中的 页 从磁盘读取到 InnoDB 缓冲池 时，有一种用于检测损坏的验证机制。此功能由 MySQL 5.5 中的 innodb_checksums 配置选项控制。innodb_checksums 在 MySQL 5.6.3 中已被弃用，并由 innodb_checksum_algorithm 替代。 In InnoDB, a validation mechanism to detect corruption when a page in a tablespace is read from disk into the InnoDB buffer pool. This feature is controlled by the innodb_checksums configuration option in MySQL 5.5. innodb_checksums is deprecated in MySQL 5.6.3, replaced by innodb_checksum_algorithm.

innochecksum 命令通过在 MySQL 服务器关闭时测试指定 表空间 文件的校验和值，帮助诊断损坏问题。The innochecksum command helps diagnose corruption problems by testing the checksum values for a specified tablespace file while the MySQL server is shut down.

MySQL 也使用校验和进行复制。有关详细信息，请参见配置选项 binlog_checksum、source_verify_checksum 或 master_verify_checksum，以及 replica_sql_verify_checksum 或 slave_sql_verify_checksum。MySQL also uses checksums for replication purposes. For details, see the configuration options binlog_checksum, source_verify_checksum or master_verify_checksum, and replica_sql_verify_checksum or slave_sql_verify_checksum.

另请参见 缓冲池、页、表空间。See Also buffer pool, page, tablespace.

在 外键 关系中，子表是指其行引用（或指向）另一张表中在特定列上具有相同值的行。这是包含 FOREIGN KEY ... REFERENCES 子句的表，并可选择性地包含 ON UPDATE 和 ON DELETE 子句。在子表中创建行之前，相应的 父表 行必须存在。子表中的值可以阻止对父表的删除或更新操作，或者根据创建外键时使用的 ON CASCADE 选项，在子表中自动执行删除或更新操作。 In a foreign key relationship, a child table is one whose rows refer (or point) to rows in another table with an identical value for a specific column. This is the table that contains the FOREIGN KEY ... REFERENCES clause and optionally ON UPDATE and ON DELETE clauses. The corresponding row in the parent table must exist before the row can be created in the child table. The values in the child table can prevent delete or update operations on the parent table, or can cause automatic deletion or updates in the child table, based on the ON CASCADE option used when creating the foreign key.

另见 外键，父表。See Also foreign key, parent table.

页 位于 InnoDB 缓冲池 中，其中所有在内存中进行的更改也已写入（刷新）到 数据文件。与 脏页 相对。 A page in the InnoDB buffer pool where all changes made in memory have also been written (flushed) to the data files. The opposite of a dirty page.

另请参见 缓冲池、数据文件、脏页、刷新、页面。See Also buffer pool, data files, dirty page, flush, page.

一个在完成前不出错并将所有更改应用到 InnoDB 表的 关闭，与 崩溃 或 快速关闭 相对。是 慢速关闭 的同义词。 A shutdown that completes without errors and applies all changes to InnoDB tables before finishing, as opposed to a crash or a fast shutdown. Synonym for slow shutdown.

另请参阅 崩溃，快速关闭，关闭，慢速关闭。See Also crash, fast shutdown, shutdown, slow shutdown.

一个在数据库服务器外运行的程序，通过发送请求到 连接器 或通过 客户端库 提供的 API 与数据库通信。它可以在与数据库服务器相同的物理机器上运行，也可以在通过网络连接的远程机器上运行。它可以是专用数据库应用程序，也可以是像 mysql 命令行处理器这样的通用程序。 A program that runs outside the database server, communicating with the database by sending requests through a Connector, or an API made available through client libraries. It can run on the same physical machine as the database server, or on a remote machine connected over a network. It can be a special-purpose database application, or a general-purpose program like the mysql command-line processor.

另请参见 API，客户端库，连接器，MySQL，服务器。See Also API, client libraries, connector, mysql, server.

包含用于数据库操作的函数集合的文件。通过使用这些库编译程序，或在与应用程序相同的系统上安装它们，您可以在没有安装 MySQL 服务器的机器上运行数据库应用程序（称为 客户端）；应用程序通过网络访问数据库。使用 MySQL 时，您可以使用 MySQL 服务器本身提供的 libmysqlclient 库。 Files containing collections of functions for working with databases. By compiling your program with these libraries, or installing them on the same system as your application, you can run a database application (known as a client) on a machine that does not have the MySQL server installed; the application accesses the database over a network. With MySQL, you can use the libmysqlclient library from the MySQL server itself.

另请参阅 客户端、libmysqlclient。See Also client, libmysqlclient.

一种 预准备语句 类型，其中缓存和重用由本地管理，模拟 服务器端预准备语句 的功能。历史上，一些 Connector/J、Connector/ODBC 和 Connector/PHP 开发人员用它来解决服务器端存储过程的问题。在现代 MySQL 服务器版本中，出于性能、可扩展性和内存效率的考虑，推荐使用服务器端预准备语句。 A type of prepared statement where the caching and reuse are managed locally, emulating the functionality of server-side prepared statements. Historically, used by some Connector/J, Connector/ODBC, and Connector/PHP developers to work around issues with server-side stored procedures. With modern MySQL server versions, server-side prepared statements are recommended for performance, scalability, and memory efficiency.

另请参见 Connector/J, Connector/ODBC, Connector/PHP, 预处理语句。See Also Connector/J, Connector/ODBC, Connector/PHP, prepared statement.

一种 SQL 数据类型（TINYTEXT、TEXT、MEDIUMTEXT 或 LONGTEXT），用于包含任意大小的任意字符数据的对象。用于存储基于文本的文档，并具有相关的字符集和排序规则。在 MySQL 应用程序中处理 CLOB 的技术根据每个 Connector 和 API 而有所不同。MySQL Connector/ODBC 将 TEXT 值定义为 LONGVARCHAR。用于存储二进制数据的等效类型是 BLOB 类型。 An SQL data type (TINYTEXT, TEXT, MEDIUMTEXT, or LONGTEXT) for objects containing any kind of character data, of arbitrary size. Used for storing text-based documents, with associated character set and collation order. The techniques for handling CLOBs within a MySQL application vary with each Connector and API. MySQL Connector/ODBC defines TEXT values as LONGVARCHAR. For storing binary data, the equivalent is the BLOB type.

另请参见 API、BLOB、连接器、Connector/ODBC。See Also API, BLOB, connector, Connector/ODBC.

InnoDB 对 主键 索引的术语。InnoDB 表存储是基于主键列的值进行组织的，以加快涉及主键列的查询和排序。为了获得最佳性能，应根据最关键性能的查询仔细选择主键列。由于修改聚集索引的列是一个开销大的操作，因此应选择很少或从不更新的主键列。 The InnoDB term for a primary key index. InnoDB table storage is organized based on the values of the primary key columns, to speed up queries and sorts involving the primary key columns. For best performance, choose the primary key columns carefully based on the most performance-critical queries. Because modifying the columns of the clustered index is an expensive operation, choose primary columns that are rarely or never updated.

在 Oracle 数据库产品中，这种类型的表被称为 索引组织表。In the Oracle Database product, this type of table is known as an index-organized table.

另请参阅 索引, 主键, 二级索引。See Also index, primary key, secondary index.

在数据库关闭时进行的备份。对于繁忙的应用程序和网站，这可能不切实际，您可能更倾向于温备份或热备份。 A backup taken while the database is shut down. For busy applications and websites, this might not be practical, and you might prefer a warm backup or a hot backup.

另见 备份，热备份，温备份。See Also backup, hot backup, warm backup.

A data item within a row, whose storage and semantics are defined by a data type. Each table以及索引 is largely defined by the set of columns it contains. A data item within a row, whose storage and semantics are defined by a data type. Each table and index is largely defined by the set of columns it contains.

Each column has a 基数 value. A column can be the primary key for its table, or part of the primary key. A column can be subject to a unique constraint, a NOT NULL constraint, or both. Values in different columns, even across different tables, can be linked by a foreign key relationship.Each column has a cardinality value. A column can be the primary key for its table, or part of the primary key. A column can be subject to a unique constraint, a NOT NULL constraint, or both. Values in different columns, even across different tables, can be linked by a foreign key relationship.

在讨论 MySQL 内部操作时，有时 字段 被用作同义词。In discussions of MySQL internal operations, sometimes field is used as a synonym.

另请参阅 基数、外键、索引、非空约束、主键、行、表、唯一约束。See Also cardinality, foreign key, index, NOT NULL constraint, primary key, row, table, unique constraint.

单列上的一个索引。 An index on a single column.

另请参见 复合索引, 索引。See Also composite index, index.

当创建 索引 并指定长度时，例如 CREATE INDEX idx ON t1 (c1(N))，索引中只存储列值的前 N 个字符。保持索引前缀较小可以使索引更紧凑，节省内存和磁盘 I/O 从而提高性能。（尽管将索引前缀设得过小可能会影响查询优化，使查询优化器认为值不同的行是重复的行。） When an index is created with a length specification, such as CREATE INDEX idx ON t1 (c1(N)), only the first N characters of the column value are stored in the index. Keeping the index prefix small makes the index compact, and the memory and disk I/O savings help performance. (Although making the index prefix too small can hinder query optimization by making rows with different values appear to the query optimizer to be duplicates.)

对于包含二进制值或长文本字符串的列，如果排序不是主要考虑因素且在索引中存储整个值会浪费空间，则索引会自动使用值的前 N 个字符（通常为 768 个字符）进行查找和排序。For columns containing binary values or long text strings, where sorting is not a major consideration and storing the entire value in the index would waste space, the index automatically uses the first N (typically 768) characters of the value to do lookups and sorts.

参见 索引。See Also index.

语句拦截器 的同义词。拦截器设计模式的一个方面，可用于 Connector/NET 和 Connector/J。Connector/NET 中称为命令的，在 Connector/J 中称为语句。与 异常拦截器 相对。 Synonym for statement interceptor. One aspect of the interceptor design pattern available for both Connector/NET and Connector/J. What Connector/NET calls a command, Connector/J refers to as a statement. Contrast with exception interceptor.

另见 Connector/J，Connector/NET，异常拦截器，拦截器，语句拦截器。See Also Connector/J, Connector/NET, exception interceptor, interceptor, statement interceptor.

一条 SQL 语句，用于结束一项 事务，使事务所做的任何更改永久生效。它与 回滚 相反，后者会撤销事务中所做的任何更改。 A SQL statement that ends a transaction, making permanent any changes made by the transaction. It is the opposite of rollback, which undoes any changes made in the transaction.

InnoDB 使用一种 乐观 的提交机制，因此更改可以在提交实际发生之前写入数据文件。这种技术使提交本身更快，但代价是如果回滚，则需要更多工作。InnoDB uses an optimistic mechanism for commits, so that changes can be written to the data files before the commit actually occurs. This technique makes the commit itself faster, with the tradeoff that more work is required in case of a rollback.

默认情况下，MySQL 使用 自动提交 设置，它会在每条 SQL 语句之后自动发出提交。By default, MySQL uses the autocommit setting, which automatically issues a commit following each SQL statement.

另请参见 自动提交、乐观、回滚、SQL、事务。See Also autocommit, optimistic, rollback, SQL, transaction.

InnoDB 表的行格式。它是从 MySQL 5.0.3 到 MySQL 5.7.8 的默认行格式。在 MySQL 8.0 中，默认行格式由 innodb_default_row_format 配置选项定义，默认设置为 DYNAMIC。COMPACT 行格式相比 REDUNDANT 行格式，为空值和可变长度列提供了更紧凑的表示。 A row format for InnoDB tables. It was the default row format from MySQL 5.0.3 to MySQL 5.7.8. In MySQL 8.0, the default row format is defined by the innodb_default_row_format configuration option, which has a default setting of DYNAMIC. The COMPACT row format provides a more compact representation for nulls and variable-length columns than the REDUNDANT row format.

有关 InnoDB COMPACT 行格式的更多信息，请参见 第 17.10 节，“InnoDB 行格式”。For additional information about InnoDB COMPACT row format, see Section 17.10, “InnoDB Row Formats”.

另请参见 动态行格式、文件格式、冗余行格式、行格式。See Also dynamic row format, file format, redundant row format, row format.

一个包含多个列的索引。 An index that includes multiple columns.

参见 索引。See Also index.

MySQL 企业备份 产品的压缩功能会为每个表空间创建压缩副本，并将扩展名从 .ibd 更改为 .ibz。压缩备份数据可以让您保留更多的备份，并减少将备份传输到其他服务器所需的时间。在恢复操作期间，数据会被解压缩。当压缩备份操作处理已经压缩的表时，它会跳过该表的压缩步骤，因为再次压缩几乎不会节省空间。 The compression feature of the MySQL Enterprise Backup product makes a compressed copy of each tablespace, changing the extension from .ibd to .ibz. Compressing backup data allows you to keep more backups on hand, and reduces the time to transfer backups to a different server. The data is uncompressed during the restore operation. When a compressed backup operation processes a table that is already compressed, it skips the compression step for that table, because compressing again would result in little or no space savings.

由 MySQL 企业备份 产品生成的一组文件，其中每个 表空间 都已压缩。压缩后的文件将重命名为 .ibz 文件扩展名。A set of files produced by the MySQL Enterprise Backup product, where each tablespace is compressed. The compressed files are renamed with a .ibz file extension.

在备份过程开始时应用压缩有助于在压缩过程中避免存储开销，并在将备份文件传输到另一台服务器时避免网络开销。应用二进制日志的过程需要更长时间，并且需要解压备份文件。Applying compression at the start of the backup process helps to avoid storage overhead during the compression process, and to avoid network overhead when transferring the backup files to another server. The process of applying the binary log takes longer, and requires uncompressing the backup files.

另请参阅 应用, 二进制日志, 压缩, 热备份, MySQL 企业备份, 表空间。See Also apply, binary log, compression, hot backup, MySQL Enterprise Backup, tablespace.

一种 行格式，可以对 InnoDB 表的数据和索引进行 压缩。大型字段会存储在与保存其余行数据的页面分开的地方，就像 动态行格式 一样。索引页和大型字段都会被压缩，从而节省内存和磁盘空间。根据数据结构的不同，内存和磁盘使用量的减少可能会抵消或不抵消解压数据时的性能开销。有关使用细节，请参见 第 17.9 节，“InnoDB 表和页面压缩”。 A row format that enables data and index compression for InnoDB tables. Large fields are stored away from the page that holds the rest of the row data, as in dynamic row format. Both index pages and the large fields are compressed, yielding memory and disk savings. Depending on the structure of the data, the decrease in memory and disk usage might or might not outweigh the performance overhead of uncompressing the data as it is used. See Section 17.9, “InnoDB Table and Page Compression” for usage details.

有关 InnoDB COMPRESSED 行格式的更多信息，请参见 DYNAMIC 行格式。For additional information about InnoDB COMPRESSED row format, see DYNAMIC Row Format.

另请参见 压缩、动态行格式、行格式。See Also compression, dynamic row format, row format.

数据以压缩形式存储的表。对于 InnoDB，这是通过 ROW_FORMAT=COMPRESSED 创建的表。有关更多信息，请参见 第 17.9 节，“InnoDB 表和页压缩”。 A table for which the data is stored in compressed form. For InnoDB, it is a table created with ROW_FORMAT=COMPRESSED. See Section 17.9, “InnoDB Table and Page Compression” for more information.

另请参见 压缩行格式、压缩。See Also compressed row format, compression.

一种功能，可带来广泛的好处，包括使用更少的磁盘空间、执行更少的 I/O 以及缓存使用更少的内存。 A feature with wide-ranging benefits from using less disk space, performing less I/O, and using less memory for caching.

InnoDB 支持表级和页级压缩。InnoDB 页压缩也称为 透明页压缩。有关 InnoDB 压缩的更多信息，请参见 第 17.9 节，“InnoDB 表和页压缩”。InnoDB supports both table-level and page-level compression. InnoDB page compression is also referred to as transparent page compression. For more information about InnoDB compression, see Section 17.9, “InnoDB Table and Page Compression”.

另一种类型的压缩是 MySQL Enterprise Backup 产品中的 压缩备份 功能。Another type of compression is the compressed backup feature of the MySQL Enterprise Backup product.

另请参见 缓冲池，压缩备份，压缩行格式，DML，透明页压缩。See Also buffer pool, compressed backup, compressed row format, DML, transparent page compression.

这实际上不是一个错误，而是在使用 压缩 与 DML 操作结合时可能发生的昂贵操作。它发生在：对压缩的 页面 的更新超出了页面上用于记录修改的区域；页面再次压缩，并将所有更改应用到表数据；重新压缩的数据无法适应原始页面，需要 MySQL 将数据拆分到两个新页面并分别压缩。要检查此情况的发生频率，请查询 INFORMATION_SCHEMA.INNODB_CMP 表，并检查 COMPRESS_OPS 列的值超过 COMPRESS_OPS_OK 列的值多少。理想情况下，压缩失败不应频繁发生；当发生时，可以调整 innodb_compression_level、innodb_compression_failure_threshold_pct 和 innodb_compression_pad_pct_max 配置选项。 Not actually an error, rather an expensive operation that can occur when using compression in combination with DML operations. It occurs when: updates to a compressed page overflow the area on the page reserved for recording modifications; the page is compressed again, with all changes applied to the table data; the re-compressed data does not fit on the original page, requiring MySQL to split the data into two new pages and compress each one separately. To check the frequency of this condition, query the INFORMATION_SCHEMA.INNODB_CMP table and check how much the value of the COMPRESS_OPS column exceeds the value of the COMPRESS_OPS_OK column. Ideally, compression failures do not occur often; when they do, you can adjust the innodb_compression_level, innodb_compression_failure_threshold_pct, and innodb_compression_pad_pct_max configuration options.

另请参见 压缩，DML，页面。See Also compression, DML, page.

多个操作（在数据库术语中，事务）同时运行而互不干扰的能力。并发还涉及性能，因为理想情况下，多重同时事务的保护应使用最低的性能开销，采用高效的锁定机制。 The ability of multiple operations (in database terminology, transactions) to run simultaneously, without interfering with each other. Concurrency is also involved with performance, because ideally the protection for multiple simultaneous transactions works with a minimum of performance overhead, using efficient mechanisms for locking.

另请参见 ACID，锁定，事务。See Also ACID, locking, transaction.

该文件保存 MySQL 启动时使用的 选项 值。传统上，在 Linux 和 Unix 系统上该文件名为 my.cnf，在 Windows 系统上则为 my.ini。你可以在文件的 [mysqld] 部分设置与 InnoDB 相关的多个选项。 The file that holds the option values used by MySQL at startup. Traditionally, on Linux and Unix this file is named my.cnf, and on Windows it is named my.ini. You can set a number of options related to InnoDB under the [mysqld] section of the file.

有关 MySQL 搜索配置文件位置的信息，请参见 第 6.2.2.2 节，“使用选项文件”。See Section 6.2.2.2, “Using Option Files” for information about where MySQL searches for configuration files.

当您使用MySQL 企业备份产品时，通常会使用两个配置文件：一个指定数据来源及其结构（这可能是服务器的原始配置文件），另一个是精简版，仅包含少量选项，指定备份数据的去向及其结构。与MySQL 企业备份产品一起使用的配置文件必须包含某些通常会被常规配置文件省略的选项，因此您可能需要在现有配置文件中添加选项以用于MySQL 企业备份。When you use the MySQL Enterprise Backup product, you typically use two configuration files: one that specifies where the data comes from and how it is structured (which could be the original configuration file for your server), and a stripped-down one containing only a small set of options that specify where the backup data goes and how it is structured. The configuration files used with the MySQL Enterprise Backup product must contain certain options that are typically left out of regular configuration files, so you might need to add options to your existing configuration file for use with MySQL Enterprise Backup.

另请参见 my.cnf，MySQL 企业备份，选项，选项文件。See Also my.cnf, MySQL Enterprise Backup, option, option file.

应用程序与 MySQL 服务器之间的通信通道。数据库应用程序的性能和可扩展性受数据库连接建立速度、可同时建立的连接数量以及连接持续时间的影响。在 Connector/NET 中，这些参数如 host、port 等被表示为 connection string，而在 Connector/ODBC 中则表示为 DSN。高流量系统使用一种称为 connection pool 的优化技术。 The communication channel between an application and a MySQL server. The performance and scalability of a database applications is influenced by on how quickly a database connection can be established, how many can be made simultaneously, and how long they persist. The parameters such as host, port, and so on are represented as a connection string in Connector/NET, and as a DSN in Connector/ODBC. High-traffic systems make use of an optimization known as the connection pool.

另请参见 连接池，连接字符串，Connector/NET，Connector/ODBC，DSN，主机，端口。See Also connection pool, connection string, Connector/NET, Connector/ODBC, DSN, host, port.

一个缓存区域，允许数据库连接在同一应用程序内或跨不同应用程序重用，而不是为每个数据库操作建立和拆除新的连接。这种技术在J2EE应用服务器中很常见。使用Connector/J的Java应用程序可以使用Tomcat和其他应用服务器的连接池功能。重用对应用程序是透明的；应用程序仍然像往常一样打开和关闭连接。 A cache area that allows database connections to be reused within the same application or across different applications, rather than setting up and tearing down a new connection for every database operation. This technique is common with J2EE application servers. Java applications using Connector/J can use the connection pool features of Tomcat and other application servers. The reuse is transparent to applications; the application still opens and closes the connection as usual.

另请参阅 连接，Connector/J，J2EE，Tomcat。See Also connection, Connector/J, J2EE, Tomcat.

数据库连接参数的表示形式，被编码为字符串字面量，以便在程序代码中使用。字符串的各个部分表示连接参数，例如主机和端口。连接字符串包含多个键值对，用分号分隔。每个键值对用等号连接。常用于Connector/NET应用程序；详情请参见创建 Connector/NET 连接字符串。 A representation of the parameters for a database connection, encoded as a string literal so that it can be used in program code. The parts of the string represent connection parameters such as host and port. A connection string contains several key-value pairs, separated by semicolons. Each key-value pair is joined with an equal sign. Frequently used with Connector/NET applications; see Creating a Connector/NET Connection String for details.

另见 连接，Connector/NET，主机，端口。See Also connection, Connector/NET, host, port.

MySQL 连接器为 客户端 程序提供与 MySQL 服务器的连接。多种编程语言和框架各自都有其关联的连接器。与由 API 提供的低级访问形成对比。 MySQL Connectors provide connectivity to the MySQL server for client programs. Several programming languages and frameworks each have their own associated Connector. Contrast with the lower-level access provided by an API.

另请参阅 API，客户端，Connector/C ，Connector/J，Connector/NET，Connector/ODBC。See Also API, client, Connector/C++, Connector/J, Connector/NET, Connector/ODBC.

Connector/C 8.0 可用于访问实现了文档存储的 MySQL 服务器，或者以传统方式使用 SQL 查询。它支持使用 X DevAPI 开发 C 应用程序，或者使用 C 的 X DevAPI 开发普通 C 应用程序。它还支持开发使用 Connector/C 1.1 的遗留基于 JDBC 的 API 的 C 应用程序。更多信息请参见 MySQL Connector/C 9.5 开发者指南。 Connector/C++ 8.0 can be used to access MySQL servers that implement a document store, or in a traditional way using SQL queries. It enables development of C++ applications using X DevAPI, or plain C applications using X DevAPI for C. It also enables development of C++ applications that use the legacy JDBC-based API from Connector/C++ 1.1. For more information, see MySQL Connector/C++ 9.5 Developer Guide.

另请参阅 客户端、连接器、JDBC。See Also client, connector, JDBC.

一个 JDBC 驱动程序，为使用 Java 编程语言开发的 客户端 应用程序提供连接。MySQL Connector/J 是一个 JDBC 类型 4 驱动程序：它是 MySQL 协议的纯 Java 实现，无需依赖 MySQL 客户端库。有关详细信息，请参见 MySQL Connector/J 开发者指南。 A JDBC driver that provides connectivity for client applications developed in the Java programming language. MySQL Connector/J is a JDBC Type 4 driver: a pure-Java implementation of the MySQL protocol that does not rely on the MySQL client libraries. For full details, see MySQL Connector/J Developer Guide.

另请参见 客户端、客户端库、连接器、Java、JDBC。See Also client, client libraries, connector, Java, JDBC.

一个 MySQL 连接器，用于开发者使用 C#、.NET、Mono、Visual Studio、ASP.net 和 ADO.net 等语言、技术和框架编写应用程序。 A MySQL connector for developers writing applications using languages, technologies, and frameworks such as C#, .NET, Mono, Visual Studio, ASP.net, and ADO.net.

另请参见 ADO.NET，ASP.net，连接器，C#，Mono，Visual Studio。See Also ADO.NET, ASP.net, connector, C#, Mono, Visual Studio.

这是一系列 MySQL ODBC 驱动程序，提供使用行业标准开放数据库连接（ODBC）API 访问 MySQL 数据库的功能。以前称为 MyODBC 驱动程序。有关完整详细信息，请参见 MySQL Connector/ODBC 开发者指南。 The family of MySQL ODBC drivers that provide access to a MySQL database using the industry standard Open Database Connectivity (ODBC) API. Formerly called MyODBC drivers. For full details, see MySQL Connector/ODBC Developer Guide.

另请参见 连接器、ODBC。See Also connector, ODBC.

针对 PHP 的 mysql 和 mysqli API 版本，针对 Windows 操作系统进行了优化。 A version of the mysql and mysqli APIs for PHP optimized for the Windows operating system.

另请参见 连接器、PHP、PHP API。See Also connector, PHP, PHP API.

一种读取操作，使用快照信息根据某个时间点呈现查询结果，而不管同时运行的其他事务所执行的更改。如果查询的数据已被其他事务更改，原始数据将根据回滚日志的内容重建。这种技术避免了一些锁定问题，这些问题可能通过强制事务等待其他事务完成而降低并发性。 A read operation that uses snapshot information to present query results based on a point in time, regardless of changes performed by other transactions running at the same time. If queried data has been changed by another transaction, the original data is reconstructed based on the contents of the undo log. This technique avoids some of the locking issues that can reduce concurrency by forcing transactions to wait for other transactions to finish.

With 可重复读 isolation level, the snapshot is based on the time when the first read operation is performed. With 已提交读 isolation level, the snapshot is reset to the time of each consistent read operation.With REPEATABLE READ isolation level, the snapshot is based on the time when the first read operation is performed. With READ COMMITTED isolation level, the snapshot is reset to the time of each consistent read operation.

一致性读取是InnoDB在已提交读和可重复读隔离级别中处理SELECT语句的默认模式。由于一致性读取不会对其访问的表设置任何锁，因此在执行一致性读取的同时，其他会话可以自由修改这些表。Consistent read is the default mode in which InnoDB processes SELECT statements in READ COMMITTED and REPEATABLE READ isolation levels. Because a consistent read does not set any locks on the tables it accesses, other sessions are free to modify those tables while a consistent read is being performed on the table.

有关适用隔离级别的技术细节，请参阅 第 17.7.2.3 节，“一致的非锁定读取”。For technical details about the applicable isolation levels, see Section 17.7.2.3, “Consistent Nonlocking Reads”.

另请参见 并发，隔离级别，锁定，已提交读，可重复读，快照，事务，回滚日志。See Also concurrency, isolation level, locking, READ COMMITTED, REPEATABLE READ, snapshot, transaction, undo log.

一种自动测试，可以阻止数据库更改，以防数据变得不一致。（在计算机科学术语中，是与不变量条件相关的一种断言。）约束是 ACID 理念的重要组成部分，用于维护数据一致性。MySQL 支持的约束包括 外键约束 和 唯一约束。 An automatic test that can block database changes to prevent data from becoming inconsistent. (In computer science terms, a kind of assertion related to an invariant condition.) Constraints are a crucial component of the ACID philosophy, to maintain data consistency. Constraints supported by MySQL include FOREIGN KEY constraints and unique constraints.

另请参阅 ACID、外键、唯一约束。See Also ACID, foreign key, unique constraint.

一个通过特定类型的 InnoDB 操作递增的值。用于衡量服务器的繁忙程度、排查性能问题的来源，以及测试更改（例如，配置设置或查询使用的索引）是否具有预期的低级效果。通过 Performance Schema 表和 INFORMATION_SCHEMA 表可以获取不同类型的计数器，特别是 INFORMATION_SCHEMA.INNODB_METRICS。 A value that is incremented by a particular kind of InnoDB operation. Useful for measuring how busy a server is, troubleshooting the sources of performance issues, and testing whether changes (for example, to configuration settings or indexes used by queries) have the desired low-level effects. Different kinds of counters are available through Performance Schema tables and INFORMATION_SCHEMA tables, particularly INFORMATION_SCHEMA.INNODB_METRICS.

另请参见 INFORMATION_SCHEMA，指标计数器，Performance Schema。See Also INFORMATION_SCHEMA, metrics counter, Performance Schema.

一个索引，包含查询所检索的所有列。查询可以直接从索引结构返回值，而不是使用索引值作为指针去查找完整的表行，这样可以节省磁盘 I/O。InnoDB 可以将这种优化技术应用于比 MyISAM 更多的索引，因为InnoDB的辅助索引也包含主键列。对于事务修改过的表上的查询，InnoDB 不能应用这种技术，直到该事务结束。 An index that includes all the columns retrieved by a query. Instead of using the index values as pointers to find the full table rows, the query returns values from the index structure, saving disk I/O. InnoDB can apply this optimization technique to more indexes than MyISAM can, because InnoDB secondary indexes also include the primary key columns. InnoDB cannot apply this technique for queries against tables modified by a transaction, until that transaction ends.

任何 列索引 或 复合索引 在合适的查询条件下都可以作为覆盖索引。尽可能设计你的索引和查询以利用这一优化技术。Any column index or composite index could act as a covering index, given the right query. Design your indexes and queries to take advantage of this optimization technique wherever possible.

另请参见 列索引、复合索引、索引、主键、二级索引。See Also column index, composite index, index, primary key, secondary index.

一种 工作负载 类型，其主要 瓶颈 是内存中的 CPU 操作。通常涉及读密集型操作，其结果都可以缓存在 缓冲池 中。 A type of workload where the primary bottleneck is CPU operations in memory. Typically involves read-intensive operations where the results can all be cached in the buffer pool.

另请参阅 瓶颈，缓冲池，工作负载。See Also bottleneck, buffer pool, workload.

MySQL 使用术语“崩溃”来一般指任何意外的关机操作，在这种情况下服务器无法进行正常的清理。例如，崩溃可能由于数据库服务器或存储设备的硬件故障、断电、可能导致 MySQL 服务器停止的潜在数据不匹配、DBA 发起的快速关闭，或许多其他原因发生。对InnoDB表的强大自动崩溃恢复确保在服务器重启时数据保持一致，DBA 无需额外操作。 MySQL uses the term “crash” to refer generally to any unexpected shutdown operation where the server cannot do its normal cleanup. For example, a crash could happen due to a hardware fault on the database server machine or storage device; a power failure; a potential data mismatch that causes the MySQL server to halt; a fast shutdown initiated by the DBA; or many other reasons. The robust, automatic crash recovery for InnoDB tables ensures that data is made consistent when the server is restarted, without any extra work for the DBA.

参见 崩溃恢复，快速关闭，InnoDB，关闭。See Also crash recovery, fast shutdown, InnoDB, shutdown.

当 MySQL 在 崩溃 后再次启动时进行的清理活动。对于 InnoDB 表，使用 重做日志 中的数据回放未完成事务的更改。在崩溃前已经 提交 但尚未写入 数据文件 的更改，可以从 双写缓冲区 中重建。当数据库正常关闭时，这类活动会在关闭期间通过 清理 操作进行。 The cleanup activities that occur when MySQL is started again after a crash. For InnoDB tables, changes from incomplete transactions are replayed using data from the redo log. Changes that were committed before the crash, but not yet written into the data files, are reconstructed from the doublewrite buffer. When the database is shut down normally, this type of activity is performed during shutdown by the purge operation.

在正常操作期间，已提交的数据可以暂时存储在变更缓冲区中，然后再写入数据文件。保持数据文件最新会在正常操作期间引入性能开销，而缓冲数据则可能导致关闭和崩溃恢复所需时间更长，这两者之间总是存在权衡。During normal operation, committed data can be stored in the change buffer for a period of time before being written to the data files. There is always a tradeoff between keeping the data files up-to-date, which introduces performance overhead during normal operation, and buffering the data, which can make shutdown and crash recovery take longer.

另见 更改缓冲区、提交、崩溃、数据文件、双写缓冲区、InnoDB、清除、重做日志。See Also change buffer, commit, crash, data files, doublewrite buffer, InnoDB, purge, redo log.

Acronym for “create, read, update, delete”, a common sequence of operations in database applications. Often denotes a class of applications with relatively simple database usage (basic DDL, DML以及query statements in SQL) that can be implemented quickly in any language. Acronym for “create, read, update, delete”, a common sequence of operations in database applications. Often denotes a class of applications with relatively simple database usage (basic DDL, DML and query statements in SQL) that can be implemented quickly in any language.

另请参见 DDL、DML、查询、SQL。See Also DDL, DML, query, SQL.

一个内部 MySQL 数据结构，表示 SQL 语句的结果集。通常与 预处理语句 和 动态 SQL 一起使用。它的工作方式类似于其他高级语言中的迭代器，可以按需从结果集中生成每个值。 An internal MySQL data structure that represents the result set of an SQL statement. Often used with prepared statements and dynamic SQL. It works like an iterator in other high-level languages, producing each value from the result set as requested.

尽管 SQL 通常会为你处理游标，但在处理性能关键的代码时，你可能会深入了解其内部工作原理。Although SQL usually handles the processing of cursors for you, you might delve into the inner workings when dealing with performance-critical code.

另请参见 动态 SQL，预处理语句，查询。See Also dynamic SQL, prepared statement, query.

追踪数据库对象（如 表、索引 以及表 列）的元数据。对于 MySQL 8.0 引入的 MySQL 数据字典，元数据物理存储在 InnoDB 每表文件 表空间文件中，位于 mysql 数据库目录中。对于 InnoDB 数据字典，元数据物理存储在 InnoDB 系统表空间 中。 Metadata that keeps track of database objects such as tables, indexes, and table columns. For the MySQL data dictionary, introduced in MySQL 8.0, metadata is physically located in InnoDB file-per-table tablespace files in the mysql database directory. For the InnoDB data dictionary, metadata is physically located in the InnoDB system tablespace.

因为 MySQL 企业备份 产品始终备份 InnoDB 系统表空间，所以所有备份都包括 InnoDB 数据字典的内容。Because the MySQL Enterprise Backup product always backs up the InnoDB system tablespace, all backups include the contents of the InnoDB data dictionary.

另请参阅 列、每表文件、.frm 文件、索引、MySQL 企业备份、系统表空间、表。See Also column, file-per-table, .frm file, index, MySQL Enterprise Backup, system tablespace, table.

每个 MySQL 实例 存放 InnoDB 的 数据文件 及表示各个数据库的目录的目录。由 datadir 配置选项控制。 The directory under which each MySQL instance keeps the data files for InnoDB and the directories representing individual databases. Controlled by the datadir configuration option.

另请参见 数据文件, 实例。See Also data files, instance.

物理包含 表 和 索引 数据的文件。 The files that physically contain table and index data.

InnoDB 系统表空间，它保存InnoDB 数据字典，并能够保存多个InnoDB表的数据，由一个或多个.ibdata数据文件表示。The InnoDB system tablespace, which holds the InnoDB data dictionary and is capable of holding data for multiple InnoDB tables, is represented by one or more .ibdata data files.

每表独立表空间，保存单个InnoDB表的数据，由一个.ibd数据文件表示。File-per-table tablespaces, which hold data for a single InnoDB table, are represented by a .ibd data file.

通用表空间（在 MySQL 5.7.6 中引入），可以保存多个InnoDB表的数据，也由一个.ibd数据文件表示。General tablespaces (introduced in MySQL 5.7.6), which can hold data for multiple InnoDB tables, are also represented by a .ibd data file.

另见 数据字典, 每表文件, 通用表空间, .ibd 文件, ibdata 文件, 索引, 系统表空间, 表, 表空间。See Also data dictionary, file-per-table, general tablespace, .ibd file, ibdata file, index, system tablespace, table, tablespace.

一个主要运行大型查询的数据库系统或应用程序。只读或大部分只读的数据可能以非规范化的形式组织以提高查询效率。可以受益于 MySQL 5.6 及更高版本中针对只读事务的优化。与OLTP形成对比。 A database system or application that primarily runs large queries. The read-only or read-mostly data might be organized in denormalized form for query efficiency. Can benefit from the optimizations for read-only transactions in MySQL 5.6 and higher. Contrast with OLTP.

另请参见 非规范化、OLTP、查询、只读事务。See Also denormalized, OLTP, query, read-only transaction.

在 MySQL 的 数据目录 中，每个数据库由一个单独的目录表示。InnoDB 系统表空间 可以存储来自 MySQL 实例 中多个数据库的表数据，它保存在位于各个数据库目录之外的 数据文件 中。当启用 每表文件 模式时，表示单个 InnoDB 表的 .ibd 文件 会存储在数据库目录内，除非使用 DATA DIRECTORY 子句在其他位置创建。MySQL 5.7.6 引入的一般表空间也会在 .ibd 文件 中存储表数据。与每表文件的 .ibd 文件 不同，一般表空间的 .ibd 文件 可以存储来自 MySQL 实例 中多个数据库的表数据，并且可以分配到相对于 MySQL 数据目录的目录或独立于 MySQL 数据目录的目录。 Within the MySQL data directory, each database is represented by a separate directory. The InnoDB system tablespace, which can hold table data from multiple databases within a MySQL instance, is kept in data files that reside outside of individual database directories. When file-per-table mode is enabled, the .ibd files representing individual InnoDB tables are stored inside the database directories unless created elsewhere using the DATA DIRECTORY clause. General tablespaces, introduced in MySQL 5.7.6, also hold table data in .ibd files. Unlike file-per-table .ibd files, general tablespace .ibd files can hold table data from multiple databases within a MySQL instance, and can be assigned to directories relative to or independent of the MySQL data directory.

对于长期使用 MySQL 的用户来说，数据库是一个熟悉的概念。来自 Oracle Database 背景的用户可能会发现，MySQL 中数据库的含义更接近 Oracle Database 所称的 模式。For long-time MySQL users, a database is a familiar notion. Users coming from an Oracle Database background may find that the MySQL meaning of a database is closer to what Oracle Database calls a schema.

另请参见 数据文件、每表文件、.ibd 文件、实例、模式、系统表空间。See Also data files, file-per-table, .ibd file, instance, schema, system tablespace.

数据控制语言，一组用于管理权限的 SQL 语句。在 MySQL 中，包括 GRANT 和 REVOKE 语句。与 DDL 和 DML 相对。 Data control language, a set of SQL statements for managing privileges. In MySQL, consists of the GRANT and REVOKE statements. Contrast with DDL and DML.

另请参见 DDL、DML、SQL。See Also DDL, DML, SQL.

一个功能，允许你在 Visual Studio 中使用数据设计工具来操作 MySQL 数据库中的架构和对象。对于使用 Connector/NET 的 MySQL 应用程序，MySQL Visual Studio 插件作为 MySQL 5.0 及更高版本的 DDEX 提供程序。 A feature that lets you use the data design tools within Visual Studio to manipulate the schema and objects within a MySQL database. For MySQL applications using Connector/NET, the MySQL Visual Studio Plugin acts as a DDEX provider with MySQL 5.0 and later.

另请参见 Visual Studio。See Also Visual Studio.

数据定义语言，一组用于操作数据库本身而非单个表行的 SQL 语句。包括所有形式的 CREATE、ALTER 和 DROP 语句。还包括 TRUNCATE 语句，因为它的工作方式与 DELETE FROM table_name 语句不同，尽管最终效果相似。 Data definition language, a set of SQL statements for manipulating the database itself rather than individual table rows. Includes all forms of the CREATE, ALTER, and DROP statements. Also includes the TRUNCATE statement, because it works differently than a DELETE FROM table_name statement, even though the ultimate effect is similar.

DDL 语句会自动 提交 当前的 事务；它们不能被 回滚。DDL statements automatically commit the current transaction; they cannot be rolled back.

InnoDB 的 在线 DDL 功能提升了 CREATE INDEX、DROP INDEX 和多种类型的 ALTER TABLE 操作的性能。有关更多信息，请参见 第 17.12 节，“InnoDB 与在线 DDL”。此外，InnoDB 的 每表文件 设置可能影响 DROP TABLE 和 TRUNCATE TABLE 操作的行为。The InnoDB online DDL feature enhances performance for CREATE INDEX, DROP INDEX, and many types of ALTER TABLE operations. See Section 17.12, “InnoDB and Online DDL” for more information. Also, the InnoDB file-per-table setting can affect the behavior of DROP TABLE and TRUNCATE TABLE operations.

与 DML 和 DCL 对比。Contrast with DML and DCL.

另见 提交、DCL、DML、每表文件、回滚、SQL、事务。See Also commit, DCL, DML, file-per-table, rollback, SQL, transaction.

一种情况，不同的事务无法继续执行，因为每个事务都持有另一个事务所需的锁。由于两个事务都在等待资源变得可用，因此没有一个事务会释放它所持有的锁。 A situation where different transactions are unable to proceed, because each holds a lock that the other needs. Because both transactions are waiting for a resource to become available, neither one ever releases the locks it holds.

当事务以相反的顺序在多个表中锁定行（通过UPDATE或SELECT ... FOR UPDATE等语句）时，可能会发生死锁。当此类语句锁定索引记录范围和空隙时，也可能发生死锁，每个事务由于时序问题获取了某些锁但未获取其他锁。A deadlock can occur when the transactions lock rows in multiple tables (through statements such as UPDATE or SELECT ... FOR UPDATE), but in the opposite order. A deadlock can also occur when such statements lock ranges of index records and gaps, with each transaction acquiring some locks but not others due to a timing issue.

有关死锁如何被自动检测和处理的背景信息，请参见 第 17.7.5.2 节，“死锁检测”。有关避免和恢复死锁情况的技巧，请参见 第 17.7.5.3 节，“如何最小化和处理死锁”。For background information on how deadlocks are automatically detected and handled, see Section 17.7.5.2, “Deadlock Detection”. For tips on avoiding and recovering from deadlock conditions, see Section 17.7.5.3, “How to Minimize and Handle Deadlocks”.

另请参见 间隙，锁，事务。See Also gap, lock, transaction.

一种机制，可以自动检测何时发生 死锁，并自动 回滚 其中一个涉及的 事务（即 受害者）。可以使用 innodb_deadlock_detect 配置选项禁用死锁检测。 A mechanism that automatically detects when a deadlock occurs, and automatically rolls back one of the transactions involved (the victim). Deadlock detection can be disabled using the innodb_deadlock_detect configuration option.

另请参阅 死锁、回滚、事务、受害者。See Also deadlock, rollback, transaction, victim.

当 InnoDB 处理 DELETE 语句时，行会立即被标记为删除，并且查询将不再返回这些行。存储空间会在稍后通过定期垃圾回收操作，即 清理（purge） 操作中回收。对于删除大量数据，相关操作及其性能特性包括 TRUNCATE 和 DROP。 When InnoDB processes a DELETE statement, the rows are immediately marked for deletion and no longer are returned by queries. The storage is reclaimed sometime later, during the periodic garbage collection known as the purge operation. For removing large quantities of data, related operations with their own performance characteristics are TRUNCATE and DROP.

另请参见 drop、purge、truncate。See Also drop, purge, truncate.

将由于 DELETE 操作而产生的二级索引页更改存储在 更改缓冲区 中，而不是立即写入的技术，以便物理写入可以以最小化随机 I/O 的方式执行。（因为删除操作是一个两步骤的过程，此操作缓冲通常用于标记索引记录删除的写入。）它是 更改缓冲 的一种类型；其他类型包括 插入缓冲 和 清除缓冲。 The technique of storing changes to secondary index pages, resulting from DELETE operations, in the change buffer rather than writing the changes immediately, so that the physical writes can be performed to minimize random I/O. (Because delete operations are a two-step process, this operation buffers the write that normally marks an index record for deletion.) It is one of the types of change buffering; the others are insert buffering and purge buffering.

另请参见 更改缓冲区、更改缓冲、插入缓冲区、插入缓冲、清除缓冲。See Also change buffer, change buffering, insert buffer, insert buffering, purge buffering.

一种数据存储策略，通过在不同表之间复制数据，而不是使用 外键 和 连接 查询来关联表。通常用于 数据仓库 应用程序，其中数据在加载后不会更新。在此类应用中，查询性能比在更新期间维持数据一致性更为重要。与 规范化 相对。 A data storage strategy that duplicates data across different tables, rather than linking the tables with foreign keys and join queries. Typically used in data warehouse applications, where the data is not updated after loading. In such applications, query performance is more important than making it simple to maintain consistent data during updates. Contrast with normalized.

另请参见 数据仓库，外键，连接，规范化。See Also data warehouse, foreign key, join, normalized.

一种索引类型，其中索引存储经过优化以处理ORDER BY column DESC子句。 A type of index where index storage is optimized to process ORDER BY column DESC clauses.

参见 索引。See Also index.

字典对象缓存将之前访问过的数据字典对象存储在内存中，以便重用对象并最小化磁盘 I/O。使用基于LRU的淘汰策略将最少使用的对象从内存中移除。该缓存由多个分区组成，每个分区存储不同类型的对象。 The dictionary object cache stores previously accessed data dictionary objects in memory to enable object reuse and minimize disk I/O. An LRU-based eviction strategy is used to evict least recently used objects from memory. The cache is comprised of several partitions that store different object types.

欲了解更多信息，请参见 第 16.4 节，“字典对象缓存”。For more information, see Section 16.4, “Dictionary Object Cache”.

另请参见 数据字典，LRU。See Also data dictionary, LRU.

InnoDB 缓冲池 中已在内存中更新的 页，其更改尚未写入（刷新）到 数据文件。与 干净页 相对。 A page in the InnoDB buffer pool that has been updated in memory, where the changes are not yet written (flushed) to the data files. The opposite of a clean page.

另请参见 缓冲池，干净页，数据文件，刷新，页。See Also buffer pool, clean page, data files, flush, page.

一种操作，它检索不可靠的数据，即由其他事务更新但尚未 提交 的数据。仅在称为 读未提交 的 隔离级别 下才可能发生。 An operation that retrieves unreliable data, data that was updated by another transaction but not yet committed. It is only possible with the isolation level known as read uncommitted.

这种操作不遵循数据库设计的ACID原则。它被认为是非常有风险的，因为数据可能会被回滚，或者在提交之前进一步更新；然后，执行脏读的事务将会使用从未确认过准确性的数据。This kind of operation does not adhere to the ACID principle of database design. It is considered very risky, because the data could be rolled back, or updated further before being committed; then, the transaction doing the dirty read would be using data that was never confirmed as accurate.

它的相反是一致性读取，在这种情况下，InnoDB确保事务不会读取被其他事务更新的信息，即使其他事务在此期间提交了。Its opposite is consistent read, where InnoDB ensures that a transaction does not read information updated by another transaction, even if the other transaction commits in the meantime.

另请参见 ACID、提交、一致性读取、隔离级别、未提交读取、回滚。See Also ACID, commit, consistent read, isolation level, READ UNCOMMITTED, rollback.

一种主要在磁盘存储（硬盘或同类设备）上组织数据的数据库。数据在磁盘和内存之间来回传输以进行操作。这与 内存数据库 相反。虽然 InnoDB 是基于磁盘的，但它也包含诸如 缓冲池、多个缓冲池实例以及 自适应哈希索引 等功能，使某些类型的工作负载可以主要从内存中运行。 A kind of database that primarily organizes data on disk storage (hard drives or equivalent). Data is brought back and forth between disk and memory to be operated upon. It is the opposite of an in-memory database. Although InnoDB is disk-based, it also contains features such as he buffer pool, multiple buffer pool instances, and the adaptive hash index that allow certain kinds of workloads to work primarily from memory.

另请参见 自适应哈希索引、缓冲池、内存数据库。See Also adaptive hash index, buffer pool, in-memory database.

一种工作负载类型，其主要瓶颈在于磁盘 I/O。（也称为I/O 受限。）通常涉及频繁写入磁盘，或随机读取的数据量大于缓冲池的容量。 A type of workload where the primary bottleneck is disk I/O. (Also known as I/O-bound.) Typically involves frequent writes to disk, or random reads of more data than can fit into the buffer pool.

另请参阅 瓶颈，缓冲池，工作负载。See Also bottleneck, buffer pool, workload.

数据操作语言，一组用于执行 INSERT、UPDATE 和 DELETE 操作的 SQL 语句。SELECT 语句有时也被认为是 DML 语句，因为 SELECT ... FOR UPDATE 形式在 锁定 方面需要考虑与 INSERT、UPDATE 和 DELETE 相同的因素。 Data manipulation language, a set of SQL statements for performing INSERT, UPDATE, and DELETE operations. The SELECT statement is sometimes considered as a DML statement, because the SELECT ... FOR UPDATE form is subject to the same considerations for locking as INSERT, UPDATE, and DELETE.

针对 InnoDB 表的 DML 语句是在 事务 的上下文中操作的，因此其效果可以作为一个单元 提交 或 回滚。DML statements for an InnoDB table operate in the context of a transaction, so their effects can be committed or rolled back as a single unit.

与 DDL 和 DCL 形成对比。Contrast with DDL and DCL.

参见 提交、DCL、DDL、锁定、回滚、SQL、事务。See Also commit, DCL, DDL, locking, rollback, SQL, transaction.

在 InnoDB 全文搜索 功能中，表中包含 FULLTEXT 索引 的特殊列，用于唯一标识与每个 ilist 值关联的文档。其名称为 FTS_DOC_ID（必须为大写）。该列本身必须为 BIGINT UNSIGNED NOT NULL 类型，并具有名为 FTS_DOC_ID_INDEX 的唯一索引。最好在创建表时定义此列。如果 InnoDB 必须在创建 FULLTEXT 索引时向表中添加该列，则索引操作的成本会显著增加。 In the InnoDB full-text search feature, a special column in the table containing the FULLTEXT index, to uniquely identify the document associated with each ilist value. Its name is FTS_DOC_ID (uppercase required). The column itself must be of BIGINT UNSIGNED NOT NULL type, with a unique index named FTS_DOC_ID_INDEX. Preferably, you define this column when creating the table. If InnoDB must add the column to the table while creating a FULLTEXT index, the indexing operation is considerably more expensive.

另请参见 全文搜索，FULLTEXT 索引，ilist。See Also full-text search, FULLTEXT index, ilist.

InnoDB 使用一种称为双写的文件刷新技术。在将 页面 写入 数据文件 之前，InnoDB 会先将它们写入一个称为双写缓冲区的存储区域。只有在写入并刷新到双写缓冲区完成后，InnoDB 才会将页面写入数据文件中的正确位置。如果在页面写入过程中操作系统、存储子系统或 mysqld 进程发生崩溃，InnoDB 可以在 崩溃恢复 期间从双写缓冲区找到页面的有效副本。 InnoDB uses a file flush technique called doublewrite. Before writing pages to the data files, InnoDB first writes them to a storage area called the doublewrite buffer. Only after the write and the flush to the doublewrite buffer have completed, does InnoDB write the pages to their proper positions in the data file. If there is an operating system, storage subsystem or mysqld process crash in the middle of a page write, InnoDB can find a good copy of the page from the doublewrite buffer during crash recovery.

虽然数据总是被写入两次，但双写缓冲区并不需要两倍的 I/O 开销或两倍的 I/O 操作。数据作为一个大的连续块写入缓冲区本身，并通过一次 fsync() 调用提交给操作系统。Although data is always written twice, the doublewrite buffer does not require twice as much I/O overhead or twice as many I/O operations. Data is written to the buffer itself as a large sequential chunk, with a single fsync() call to the operating system.

另请参见 崩溃恢复、数据文件、页、清除。See Also crash recovery, data files, page, purge.

一种 DDL 操作，用于通过诸如 DROP TABLE 或 DROP INDEX 之类的语句删除模式对象。它在内部映射为 ALTER TABLE 语句。从 InnoDB 的角度来看，此类操作的性能考虑涉及锁定 数据字典 以确保所有相关对象都得到更新的时间，以及更新内存结构（如 缓冲池）的时间。对于 表 来说，删除操作与 截断 操作（TRUNCATE TABLE 语句）具有略微不同的特性。 A kind of DDL operation that removes a schema object, through a statement such as DROP TABLE or DROP INDEX. It maps internally to an ALTER TABLE statement. From an InnoDB perspective, the performance considerations of such operations involve the time that the data dictionary is locked to ensure that interrelated objects are all updated, and the time to update memory structures such as the buffer pool. For a table, the drop operation has somewhat different characteristics than a truncate operation (TRUNCATE TABLE statement).

另请参见 缓冲池，数据字典，DDL，表，截断。See Also buffer pool, data dictionary, DDL, table, truncate.

Acronym for “Database Source Name”. It is the encoding for connection information within Connector/ODBC。参见Configuring a Connector/ODBC DSN on Windows for full details. It is the equivalent of the connection string used by Connector/NET. Acronym for “Database Source Name”. It is the encoding for connection information within Connector/ODBC. See Configuring a Connector/ODBC DSN on Windows for full details. It is the equivalent of the connection string used by Connector/NET.

另请参见 连接、连接字符串、Connector/NET、Connector/ODBC。See Also connection, connection string, Connector/NET, Connector/ODBC.

一种由 ODBC 支持的 游标 类型，可以在再次读取行时获取新增和更改的结果。更改是否以及多快对游标可见，取决于所涉及的表类型（事务性或非事务性）以及事务性表的隔离级别。必须显式启用对动态游标的支持。 A type of cursor supported by ODBC that can pick up new and changed results when the rows are read again. Whether and how quickly the changes are visible to the cursor depends on the type of table involved (transactional or non-transactional) and the isolation level for transactional tables. Support for dynamic cursors must be explicitly enabled.

另请参见 光标、ODBC。See Also cursor, ODBC.

一种 InnoDB 行格式。由于长变长列值存储在包含行数据的页面之外，它对于包含大型对象的行非常高效。由于这些大字段通常不用于评估查询条件，因此它们不经常被加载到 缓冲池 中，从而减少了 I/O 操作并提高了缓存内存的利用率。 An InnoDB row format. Because long variable-length column values are stored outside of the page that holds the row data, it is very efficient for rows that include large objects. Since the large fields are typically not accessed to evaluate query conditions, they are not brought into the buffer pool as often, resulting in fewer I/O operations and better utilization of cache memory.

从 MySQL 5.7.9 开始，默认行格式由 innodb_default_row_format 定义，其默认值为 DYNAMIC。As of MySQL 5.7.9, the default row format is defined by innodb_default_row_format, which has a default value of DYNAMIC.

关于 InnoDB DYNAMIC 行格式的更多信息，请参见 DYNAMIC 行格式。For additional information about InnoDB DYNAMIC row format, see DYNAMIC Row Format.

另请参见 缓冲池，文件格式，行格式。See Also buffer pool, file format, row format.

一种功能，使您能够使用比将语句各部分连接成字符串变量的简单方法更强大、更安全且更高效的方法来创建和执行预处理语句以替换参数值。 A feature that lets you create and execute prepared statements using more robust, secure, and efficient methods to substitute parameter values than the naive technique of concatenating the parts of the statement into a string variable.

另请参见 预处理语句。See Also prepared statement.

通过动态 SQL创建并执行的预处理语句。 A prepared statement created and executed through dynamic SQL.

另请参见 动态 SQL, 预处理语句。See Also dynamic SQL, prepared statement.

类似于 Beta 阶段，当软件产品通常在非关键任务环境中评估其性能、功能和兼容性时的阶段。 A stage similar to beta, when a software product is typically evaluated for performance, functionality, and compatibility in a non-mission-critical setting.

另见 Beta。See Also beta.

一种包含许多面向对象特性的编程语言。它的一些概念对 Java 和 C# 开发者来说很熟悉。有关 MySQL 的开源 Eiffel API，请参见 31.13 节，“MySQL Eiffel 包装器”。 A programming language including many object-oriented features. Some of its concepts are familiar to Java and C# developers. For the open-source Eiffel API for MySQL, see Section 31.13, “MySQL Eiffel Wrapper”.

参见 API，C#，Java。See Also API, C#, Java.

嵌入式 MySQL 服务器库（libmysqld）使在 客户端 应用程序中运行功能完整的 MySQL 服务器成为可能。主要优点是提高速度，并使嵌入式应用程序的管理更简单。 The embedded MySQL server library (libmysqld) makes it possible to run a full-featured MySQL server inside a client application. The main benefits are increased speed and more simple management for embedded applications.

参见 客户端，libmysqld。See Also client, libmysqld.

一种日志，显示 MySQL 启动信息、关键运行时错误和崩溃信息。详情见 第 7.4.2 节，“错误日志”。 A type of log showing information about MySQL startup and critical runtime errors and crash information. For details, see Section 7.4.2, “The Error Log”.

另请参见 崩溃、日志。See Also crash, log.

从缓存或其他临时存储区域中移除某个项目的过程，例如 InnoDB 缓冲池。通常，但并非总是，会使用 LRU 算法来确定要移除的项目。当 脏页 被驱逐时，其内容会被 刷新 到磁盘，并且任何脏的 邻页 也可能被刷新。 The process of removing an item from a cache or other temporary storage area, such as the InnoDB buffer pool. Often, but not always, uses the LRU algorithm to determine which item to remove. When a dirty page is evicted, its contents are flushed to disk, and any dirty neighbor pages might be flushed also.

另请参阅 缓冲池、脏页、刷新、LRU、邻页。See Also buffer pool, dirty page, flush, LRU, neighbor page.

一种用于跟踪、调试或增强数据库应用程序遇到的 SQL 错误的 拦截器 类型。例如，拦截器代码可以发出 SHOW WARNINGS 语句以检索额外信息，并添加描述性文本甚至更改返回给应用程序的异常类型。由于只有在 SQL 语句返回错误时才会调用拦截器代码，因此在正常（无错误）操作期间，它不会对应用程序性能产生任何影响。 A type of interceptor for tracing, debugging, or augmenting SQL errors encountered by a database application. For example, the interceptor code could issue a SHOW WARNINGS statement to retrieve additional information, and add descriptive text or even change the type of the exception returned to the application. Because the interceptor code is only called when SQL statements return errors, it does not impose any performance penalty on the application during normal (error-free) operation.

在使用 Connector/J 的 Java 应用程序中，设置这种类型的拦截器涉及实现 com.mysql.jdbc.ExceptionInterceptor 接口，并向 连接字符串 添加一个 exceptionInterceptors 属性。In Java applications using Connector/J, setting up this type of interceptor involves implementing the com.mysql.jdbc.ExceptionInterceptor interface, and adding a exceptionInterceptors property to the connection string.

在使用 Connector/NET 的 Visual Studio 应用程序中，设置这种类型的拦截器涉及定义一个继承自 BaseExceptionInterceptor 类的类，并在连接字符串中指定该类名。In Visual Studio applications using Connector/NET, setting up this type of interceptor involves defining a class that inherits from the BaseExceptionInterceptor class and specifying that class name as part of the connection string.

另请参阅 Connector/J，Connector/NET，拦截器，Java，Visual Studio。See Also Connector/J, Connector/NET, interceptor, Java, Visual Studio.

一种锁，可以防止任何其他事务锁定同一行。根据事务的隔离级别，这种锁可能会阻止其他事务写入同一行，或者也可能阻止其他事务读取同一行。默认的InnoDB隔离级别可重复读通过允许事务读取具有独占锁的行，从而提高了并发性，这种技术称为一致性读。 A kind of lock that prevents any other transaction from locking the same row. Depending on the transaction isolation level, this kind of lock might block other transactions from writing to the same row, or might also block other transactions from reading the same row. The default InnoDB isolation level, REPEATABLE READ, enables higher concurrency by allowing transactions to read rows that have exclusive locks, a technique known as consistent read.

另请参见 并发，一致性读取，隔离级别，锁，可重复读，共享锁，事务。See Also concurrency, consistent read, isolation level, lock, REPEATABLE READ, shared lock, transaction.

A group of 预读 within a tablespace. For the default page size of 16KB, an extent contains 64 pages. In MySQL 5.6, the page size for an InnoDB instance can be 4KB, 8KB, or 16KB, controlled by the innodb_page_size configuration option. For 4KB, 8KB, and 16KB pages sizes, the extent size is always 1MB (or 1048576 bytes). A group of pages within a tablespace. For the default page size of 16KB, an extent contains 64 pages. In MySQL 5.6, the page size for an InnoDB instance can be 4KB, 8KB, or 16KB, controlled by the innodb_page_size configuration option. For 4KB, 8KB, and 16KB pages sizes, the extent size is always 1MB (or 1048576 bytes).

在 MySQL 5.7.6 中添加了对 32KB 和 64KB InnoDB 页面大小的支持。对于 32KB 页面大小，区的大小为 2MB。对于 64KB 页面大小，区的大小为 4MB。Support for 32KB and 64KB InnoDB page sizes was added in MySQL 5.7.6. For a 32KB page size, the extent size is 2MB. For a 64KB page size, the extent size is 4MB.

InnoDB 的特性，例如 段、预读 请求和 双写缓冲区 使用的一次 I/O 操作是以单个区（extent）为单位进行读取、写入、分配或释放数据的。InnoDB features such as segments, read-ahead requests and the doublewrite buffer use I/O operations that read, write, allocate, or free data one extent at a time.

另请参见 双写缓冲区、页、页大小、预读、段、表空间。See Also doublewrite buffer, page, page size, read-ahead, segment, tablespace.

一个包含 MySQL 表的元数据（例如表定义）的文件。.frm 文件在 MySQL 8.0 中被移除，但在早期的 MySQL 版本中仍然使用。在 MySQL 8.0 中，之前存储在 .frm 文件中的数据存储在 数据字典 表中。 A file containing the metadata, such as the table definition, of a MySQL table. .frm files were removed in MySQL 8.0 but are still used in earlier MySQL releases. In MySQL 8.0, data previously stored in .frm files is stored in data dictionary tables.

另请参阅 数据字典、MySQL 企业备份、系统表空间。See Also data dictionary, MySQL Enterprise Backup, system tablespace.

在发生故障时能够自动切换到备用服务器的能力。在 MySQL 的上下文中，故障转移涉及一个备用数据库服务器。通常由应用服务器或框架在 J2EE 环境中支持。 The ability to automatically switch to a standby server in the event of a failure. In the MySQL context, failover involves a standby database server. Often supported within J2EE environments by the application server or framework.

另见 Connector/J, J2EE。See Also Connector/J, J2EE.

最初在 InnoDB 插件中引入的功能，现在在 MySQL 5.5 及更高版本中已成为一部分，该功能通过避免完全重写关联表，加快了 InnoDB 二级索引 的创建速度。该加速也适用于删除二级索引。 A capability first introduced in the InnoDB Plugin, now part of MySQL in 5.5 and higher, that speeds up creation of InnoDB secondary indexes by avoiding the need to completely rewrite the associated table. The speedup applies to dropping secondary indexes also.

由于索引维护可能会增加许多数据传输操作的性能开销，因此可以考虑在没有任何二级索引的情况下执行诸如ALTER TABLE ... ENGINE=INNODB或INSERT INTO ... SELECT * FROM ...之类的操作，然后再创建索引。Because index maintenance can add performance overhead to many data transfer operations, consider doing operations such as ALTER TABLE ... ENGINE=INNODB or INSERT INTO ... SELECT * FROM ... without any secondary indexes in place, and creating the indexes afterward.

在 MySQL 5.6 中，这一功能变得更通用。您可以在索引创建过程中对表进行读写操作，并且许多类型的ALTER TABLE操作可以在不复制表、不阻塞DML操作或二者皆不的情况下执行。因此，在 MySQL 5.6 及更高版本中，这组功能被称为在线 DDL，而不是快速索引创建。In MySQL 5.6, this feature becomes more general. You can read and write to tables while an index is being created, and many more kinds of ALTER TABLE operations can be performed without copying the table, without blocking DML operations, or both. Thus in MySQL 5.6 and higher, this set of features is referred to as online DDL rather than Fast Index Creation.

有关相关信息，请参见 第 17.12 节，“InnoDB 与在线 DDL”。For related information, see Section 17.12, “InnoDB and Online DDL”.

另请参见 DML、索引、在线 DDL、辅助索引。See Also DML, index, online DDL, secondary index.

基于配置设置 innodb_fast_shutdown=1，InnoDB 的默认 关闭 程序。为了节省时间，某些 刷新 操作会被跳过。这种类型的关闭在正常使用期间是安全的，因为刷新操作会在下一次启动时执行，使用与 崩溃恢复 相同的机制。在数据库因升级或降级而关闭的情况下，应执行 慢速关闭，以确保所有相关更改在关闭期间应用到 数据文件 中。 The default shutdown procedure for InnoDB, based on the configuration setting innodb_fast_shutdown=1. To save time, certain flush operations are skipped. This type of shutdown is safe during normal usage, because the flush operations are performed during the next startup, using the same mechanism as in crash recovery. In cases where the database is being shut down for an upgrade or downgrade, do a slow shutdown instead to ensure that all relevant changes are applied to the data files during the shutdown.

另请参见 崩溃恢复、数据文件、刷新、关闭、慢速关闭。See Also crash recovery, data files, flush, shutdown, slow shutdown.

InnoDB 表的文件格式。 The file format for InnoDB tables.

另请参见 每表文件、.ibd 文件、ibdata 文件、行格式。See Also file-per-table, .ibd file, ibdata file, row format.

这是由 innodb_file_per_table 选项控制的设置的一般名称，该选项是一个重要的配置选项，影响 InnoDB 文件存储、功能可用性和 I/O 特性。从 MySQL 5.6.7 起，innodb_file_per_table 默认启用。 A general name for the setting controlled by the innodb_file_per_table option, which is an important configuration option that affects aspects of InnoDB file storage, availability of features, and I/O characteristics. As of MySQL 5.6.7, innodb_file_per_table is enabled by default.

启用innodb_file_per_table option enabled, you can create a table in its own .ibd file rather than in the shared ibdata files of the system tablespace. When table data is stored in an individual .ibd file, you have more flexibility to choose row formats required for features such as data compression. The TRUNCATE TABLE operation is also faster, and reclaimed space can be used by the operating system rather than remaining reserved for InnoDB.With the innodb_file_per_table option enabled, you can create a table in its own .ibd file rather than in the shared ibdata files of the system tablespace. When table data is stored in an individual .ibd file, you have more flexibility to choose row formats required for features such as data compression. The TRUNCATE TABLE operation is also faster, and reclaimed space can be used by the operating system rather than remaining reserved for InnoDB.

MySQL 企业备份 产品对于存储在其自身文件中的表更为灵活。例如，表可以从备份中排除，但前提是它们在单独的文件中。因此，此设置适用于备份频率较低或按不同时间表备份的表。The MySQL Enterprise Backup product is more flexible for tables that are in their own files. For example, tables can be excluded from a backup, but only if they are in separate files. Thus, this setting is suitable for tables that are backed up less frequently or on a different schedule.

另请参见 压缩行格式、压缩、文件格式、.ibd 文件、ibdata 文件、innodb_file_per_table、MySQL 企业备份、行格式、系统表空间。See Also compressed row format, compression, file format, .ibd file, ibdata file, innodb_file_per_table, MySQL Enterprise Backup, row format, system tablespace.

在一个 InnoDB 索引 中，页 被索引数据占用的比例在页分裂之前称为填充因子。当索引数据首次在页之间分配时的未使用空间允许行在更新为更长的字符串值时无需进行昂贵的索引维护操作。如果填充因子过低，索引会占用比需要更多的空间，从而在读取索引时造成额外的 I/O 负担。如果填充因子过高，任何增加列值长度的更新都会导致索引维护的额外 I/O 负担。有关更多信息，请参见 第 17.6.2.2 节，“InnoDB 索引的物理结构”。 In an InnoDB index, the proportion of a page that is taken up by index data before the page is split. The unused space when index data is first divided between pages allows for rows to be updated with longer string values without requiring expensive index maintenance operations. If the fill factor is too low, the index consumes more space than needed, causing extra I/O overhead when reading the index. If the fill factor is too high, any update that increases the length of column values can cause extra I/O overhead for index maintenance. See Section 17.6.2.2, “The Physical Structure of an InnoDB Index” for more information.

另请参阅 索引, 页。See Also index, page.

这种行格式由 MyISAM 存储引擎使用，而不是 InnoDB。如果在 MySQL 5.7.6 或更早版本中使用选项 ROW_FORMAT=FIXED 创建 InnoDB 表，InnoDB 会改为使用 紧凑行格式，尽管在输出中（例如 SHOW TABLE STATUS 报告）FIXED 值仍可能显示。自 MySQL 5.7.7 起，如果指定 ROW_FORMAT=FIXED，InnoDB 将返回错误。 This row format is used by the MyISAM storage engine, not by InnoDB. If you create an InnoDB table with the option ROW_FORMAT=FIXED in MySQL 5.7.6 or earlier, InnoDB uses the compact row format instead, although the FIXED value might still show up in output such as SHOW TABLE STATUS reports. As of MySQL 5.7.7, InnoDB returns an error if ROW_FORMAT=FIXED is specified.

另见 紧凑行格式，行格式。See Also compact row format, row format.

将缓存在内存区域或临时磁盘存储区域中的更改写入数据库文件。InnoDB 存储结构中定期刷新的包括 重做日志、回滚日志 以及 缓冲池。 To write changes to the database files, that had been buffered in a memory area or a temporary disk storage area. The InnoDB storage structures that are periodically flushed include the redo log, the undo log, and the buffer pool.

刷新可能发生的原因是内存区域已满，系统需要释放一些空间，因为 提交 操作意味着事务的更改可以被最终确定，或者因为 缓慢关闭 操作意味着所有未完成的工作都应当被最终确定。当不需要一次性刷新所有缓冲数据时，InnoDB 可以使用一种称为 模糊检查点 的技术，将页面分批刷新以分散 I/O 开销。Flushing can happen because a memory area becomes full and the system needs to free some space, because a commit operation means the changes from a transaction can be finalized, or because a slow shutdown operation means that all outstanding work should be finalized. When it is not critical to flush all the buffered data at once, InnoDB can use a technique called fuzzy checkpointing to flush small batches of pages to spread out the I/O overhead.

另请参见 缓冲池，提交，模糊检查点，重做日志，慢速关闭，回滚日志。See Also buffer pool, commit, fuzzy checkpointing, redo log, slow shutdown, undo log.

一个内部的 InnoDB 数据结构，用于跟踪 脏页 在 缓冲池 中的状态：也就是说，已经被修改并需要写回磁盘的 页。这个数据结构由 InnoDB 内部的 小事务 经常更新，因此它由自己的 互斥锁 保护，以允许对缓冲池的并发访问。 An internal InnoDB data structure that tracks dirty pages in the buffer pool: that is, pages that have been changed and need to be written back out to disk. This data structure is updated frequently by InnoDB internal mini-transactions, and so is protected by its own mutex to allow concurrent access to the buffer pool.

另请参阅 缓冲池，脏页，LRU，微事务，互斥锁，页，页清理器。See Also buffer pool, dirty page, LRU, mini-transaction, mutex, page, page cleaner.

一种指针类型的关系，存在于不同 InnoDB 表的行之间。外键关系在 父表 和 子表 中的某一列上定义。 A type of pointer relationship, between rows in separate InnoDB tables. The foreign key relationship is defined on one column in both the parent table and the child table.

除了能够快速查找相关信息之外，外键还有助于强制执行参照完整性，通过防止在插入、更新和删除数据时这些指针中的任何一个变得无效。这种执行机制是一种约束。如果一个行指向另一张表，但关联的外键值在另一张表中不存在，则不能插入该行。如果删除一行或其外键值被更改，并且另一张表中的行指向该外键值，则可以设置外键来防止删除、使另一张表中的相应列值变为空，或者自动删除另一张表中的对应行。In addition to enabling fast lookup of related information, foreign keys help to enforce referential integrity, by preventing any of these pointers from becoming invalid as data is inserted, updated, and deleted. This enforcement mechanism is a type of constraint. A row that points to another table cannot be inserted if the associated foreign key value does not exist in the other table. If a row is deleted or its foreign key value changed, and rows in another table point to that foreign key value, the foreign key can be set up to prevent the deletion, cause the corresponding column values in the other table to become null, or automatically delete the corresponding rows in the other table.

设计一个规范化数据库的阶段之一是识别重复的数据，将这些数据分离到一个新表中，并建立外键关系，以便使用连接操作像查询单个表一样查询多个表。One of the stages in designing a normalized database is to identify data that is duplicated, separate that data into a new table, and set up a foreign key relationship so that the multiple tables can be queried like a single table, using a join operation.

另请参阅 子表、外键约束、连接、规范化、NULL、主表、参照完整性、关系型。See Also child table, FOREIGN KEY constraint, join, normalized, NULL, parent table, referential integrity, relational.

维护数据库一致性的约束类型，通过外键关系实现。像其他类型的约束一样，如果数据可能变得不一致，它可以阻止数据被插入或更新；在这种情况下，被防止的不一致性是多表之间的数据不一致。或者，当执行DML操作时，FOREIGN KEY约束可以根据创建外键时指定的ON CASCADE选项，导致子行的数据被删除、更改为不同的值，或者设置为空值。 The type of constraint that maintains database consistency through a foreign key relationship. Like other kinds of constraints, it can prevent data from being inserted or updated if data would become inconsistent; in this case, the inconsistency being prevented is between data in multiple tables. Alternatively, when a DML operation is performed, FOREIGN KEY constraints can cause data in child rows to be deleted, changed to different values, or set to null, based on the ON CASCADE option specified when creating the foreign key.

另请参见 子表、约束、DML、外键、NULL。See Also child table, constraint, DML, foreign key, NULL.

在大多数情况下，是 全文搜索 的缩写。有时在性能讨论中，是 全表扫描 的缩写。 In most contexts, an acronym for full-text search. Sometimes in performance discussions, an acronym for full table scan.

另请参见 全表扫描、全文搜索。See Also full table scan, full-text search.

包含每个 MySQL 数据库中所有 表以及 MySQL 实例中所有数据库的 备份。与 部分备份对比。 A backup that includes all the tables in each MySQL database, and all the databases in a MySQL instance. Contrast with partial backup.

另见 备份，数据库，实例，部分备份，表。See Also backup, database, instance, partial backup, table.

一种操作，需要读取表的全部内容，而不仅仅是使用 索引 选择的部分内容。通常在小型查找表中执行，或者在数据仓库中处理大型表时执行，此时会聚合和分析所有可用数据。这些操作发生的频率以及表的大小相对于可用内存的情况，会影响查询优化和 缓冲池 管理中使用的算法。 An operation that requires reading the entire contents of a table, rather than just selected portions using an index. Typically performed either with small lookup tables, or in data warehousing situations with large tables where all available data is aggregated and analyzed. How frequently these operations occur, and the sizes of the tables relative to available memory, have implications for the algorithms used in query optimization and managing the buffer pool.

索引的目的是允许在大型表中查找特定值或值范围，从而在可行时避免全表扫描。The purpose of indexes is to allow lookups for specific values or ranges of values within a large table, thus avoiding full table scans when practical.

参见 缓冲池，索引。See Also buffer pool, index.

MySQL 用于在表数据中查找单词、短语、单词的布尔组合等的功能，比使用 SQL LIKE 操作符或编写自己的应用级搜索算法更快、更方便、更灵活。它使用 SQL 函数 MATCH() 和 FULLTEXT 索引。 The MySQL feature for finding words, phrases, Boolean combinations of words, and so on within table data, in a faster, more convenient, and more flexible way than using the SQL LIKE operator or writing your own application-level search algorithm. It uses the SQL function MATCH() and FULLTEXT indexes.

另请参见 FULLTEXT 索引。See Also FULLTEXT index.

MySQL 全文搜索机制中用于存储搜索索引的特殊类型的索引。表示列值中的单词，省略任何被指定为停用词的单词。最初，仅适用于MyISAM表。从 MySQL 5.6.4 起，它也适用于InnoDB表。 The special kind of index that holds the search index in the MySQL full-text search mechanism. Represents the words from values of a column, omitting any that are specified as stopwords. Originally, only available for MyISAM tables. Starting in MySQL 5.6.4, it is also available for InnoDB tables.

另请参阅 全文搜索、索引、InnoDB、搜索索引、停用词。See Also full-text search, index, InnoDB, search index, stopword.

一种技术，可从 缓冲池中刷新少量的脏页，而不是一次性刷新所有脏页，这样会干扰数据库处理。 A technique that flushes small batches of dirty pages from the buffer pool, rather than flushing all dirty pages at once which would disrupt database processing.

另请参见 缓冲池、脏页、刷写。See Also buffer pool, dirty page, flush.

“一般可用”，指软件产品离开 测试版 阶段，并可供销售、官方支持和生产使用的阶段。 “Generally available”, the stage when a software product leaves beta and is available for sale, official support, and production use.

另见 Beta。See Also beta.

Acronym for “Global Assembly Cache”. A central area for storing libraries (assemblies) on a .NET system. Physically consists of nested folders, treated as a single virtual folder by the .NET CLR.

另请参见 .NET，程序集。See Also .NET, assembly.

在 InnoDB 索引 数据结构中可以插入新值的位置。当你使用诸如 SELECT ... FOR UPDATE 的语句锁定一组行时，InnoDB 可以创建既作用于间隙也作用于索引中实际值的锁。例如，如果你选择所有大于 10 的值进行更新，间隙锁会防止其他事务插入一个大于 10 的新值。上确界记录 和 下确界记录 表示包含所有大于或小于当前索引值的间隙。 A place in an InnoDB index data structure where new values could be inserted. When you lock a set of rows with a statement such as SELECT ... FOR UPDATE, InnoDB can create locks that apply to the gaps as well as the actual values in the index. For example, if you select all values greater than 10 for update, a gap lock prevents another transaction from inserting a new value that is greater than 10. The supremum record and infimum record represent the gaps containing all values greater than or less than all the current index values.

另请参见 并发，间隙锁，索引，下界记录，隔离级别，上界记录。See Also concurrency, gap lock, index, infimum record, isolation level, supremum record.

A lock on a 间隙 between index records, or a lock on the gap before the first or after the last index record. For example, SELECT c1 FROM t WHERE c1 BETWEEN 10 and 20 FOR UPDATE; prevents other transactions from inserting a value of 15 into the column t.c1, whether or not there was already any such value in the column, because the gaps between all existing values in the range are locked. Contrast with record lock以及next-key lock. A lock on a gap between index records, or a lock on the gap before the first or after the last index record. For example, SELECT c1 FROM t WHERE c1 BETWEEN 10 and 20 FOR UPDATE; prevents other transactions from inserting a value of 15 into the column t.c1, whether or not there was already any such value in the column, because the gaps between all existing values in the range are locked. Contrast with record lock and next-key lock.

空隙锁是性能与 并发性 之间权衡的一部分，并且在某些事务 隔离级别 中使用，而在其他隔离级别中不使用。Gap locks are part of the tradeoff between performance and concurrency, and are used in some transaction isolation levels and not others.

另见 空隙，下确界记录，锁，下一个键锁，记录锁，上确界记录。See Also gap, infimum record, lock, next-key lock, record lock, supremum record.

一种用于诊断和排查 MySQL 服务器处理的 SQL 语句的 日志。可以存储在文件中或表中。要使用此功能，必须通过 general_log 配置选项启用它。你可以通过 sql_log_off 配置选项为特定连接禁用它。 A type of log used for diagnosis and troubleshooting of SQL statements processed by the MySQL server. Can be stored in a file or in a database table. You must enable this feature through the general_log configuration option to use it. You can disable it for a specific connection through the sql_log_off configuration option.

记录的查询范围比慢查询日志更广。与用于复制的二进制日志不同，通用查询日志包含SELECT语句，并且不保持严格的顺序。更多信息，请参见第 7.4.3 节，“通用查询日志”。Records a broader range of queries than the slow query log. Unlike the binary log, which is used for replication, the general query log contains SELECT statements and does not maintain strict ordering. For more information, see Section 7.4.3, “The General Query Log”.

另请参见 二进制日志、日志、慢查询日志。See Also binary log, log, slow query log.

使用 CREATE TABLESPACE 语法创建的共享 InnoDB 表空间。通用表空间可以在 MySQL 数据目录外创建，能够容纳多个 表，并支持所有行格式的表。通用表空间是在 MySQL 5.7.6 中引入的。 A shared InnoDB tablespace created using CREATE TABLESPACE syntax. General tablespaces can be created outside of the MySQL data directory, are capable of holding multiple tables, and support tables of all row formats. General tablespaces were introduced in MySQL 5.7.6.

表可以使用 CREATE TABLE tbl_name ... TABLESPACE [=] tablespace_name 或 ALTER TABLE tbl_name TABLESPACE [=] tablespace_name 语法添加到通用表空间中。Tables are added to a general tablespace using CREATE TABLE tbl_name ... TABLESPACE [=] tablespace_name or ALTER TABLE tbl_name TABLESPACE [=] tablespace_name syntax.

与 系统表空间 和 每表文件表空间 相对照。Contrast with system tablespace and file-per-table tablespace.

更多信息，请参见 第 17.6.3.3 节，“通用表空间”。For more information, see Section 17.6.3.3, “General Tablespaces”.

另请参见 每表文件、系统表空间、表、表空间。See Also file-per-table, system tablespace, table, tablespace.

一列，其值由包含在列定义中的表达式计算得出。生成列可以是 虚拟 或 存储 的。 A column whose values are computed from an expression included in the column definition. A generated column can be virtual or stored.

参见 基本列，存储生成列，虚拟生成列。See Also base column, stored generated column, virtual generated column.

参见 J2EE。See Also J2EE.

一个临时表空间，用于存储用户创建的临时表所进行更改的回滚段。 A temporary tablespace that stores rollback segments for changes made to user-created temporary tables.

另请参见 临时表空间。See Also temporary tablespace.

一种涉及 XA 操作的 事务 类型。它由若干本身是事务的操作组成，但所有操作必须要么作为一个整体成功完成，要么全部回滚。实质上，这扩展了 ACID 特性 “提升一级”，使得多个 ACID 事务能够协同执行，作为也具有 ACID 特性的全局操作的组成部分。 A type of transaction involved in XA operations. It consists of several actions that are transactional in themselves, but that all must either complete successfully as a group, or all be rolled back as a group. In essence, this extends ACID properties “up a level” so that multiple ACID transactions can be executed in concert as components of a global operation that also has ACID properties.

参见 ACID、事务、XA。See Also ACID, transaction, XA.

一种 InnoDB 优化，它对一组 提交 操作仅执行一次某些低级别的 I/O 操作（日志写入），而不是为每个提交单独刷新和同步。 An InnoDB optimization that performs some low-level I/O operations (log write) once for a set of commit operations, rather than flushing and syncing separately for each commit.

另见 二进制日志, 提交。See Also binary log, commit.

Acronym for “globally unique identifier”, an ID value that can be used to associate data across different databases, languages, operating systems, and so on. (As an alternative to using sequential integers, where the same values could appear in different tables, databases, and so on referring to different data.) Older MySQL versions represented it as BINARY(16). Currently, it is represented as CHAR(36). MySQL has a UUID() function that returns GUID values in character format, and a UUID_SHORT() function that returns GUID values in integer format. Because successive GUID values are not necessarily in ascending sort order, it is not an efficient value to use as a primary key for large InnoDB tables.

一种用于使用等值运算符而不是大于或 BETWEEN 等范围运算符的查询的 索引 类型。它适用于 MEMORY 表。尽管出于历史原因哈希索引是 MEMORY 表的默认索引，但该存储引擎也支持 B 树 索引，对于通用查询通常是更好的选择。 A type of index intended for queries that use equality operators, rather than range operators such as greater-than or BETWEEN. It is available for MEMORY tables. Although hash indexes are the default for MEMORY tables for historic reasons, that storage engine also supports B-tree indexes, which are often a better choice for general-purpose queries.

MySQL 包含这种索引类型的一个变体，自适应哈希索引，如果需要，它会根据运行时条件自动为InnoDB表构建。MySQL includes a variant of this index type, the adaptive hash index, that is constructed automatically for InnoDB tables if needed based on runtime conditions.

另请参见 自适应哈希索引、B 树、索引、InnoDB。See Also adaptive hash index, B-tree, index, InnoDB.

Acronym for “hard disk drive”. Refers to storage media using spinning platters, usually when comparing and contrasting with SSD. Its performance characteristics can influence the throughput of a disk-based workload.

另见 基于磁盘，SSD。See Also disk-based, SSD.

定期发送的一条消息，用于指示系统运行正常。在复制环境中，如果源停止发送此类消息，其中一个副本可以接替它的位置。类似的技术可以在集群环境中的服务器之间使用，以确认它们全部正常运行。 A periodic message that is sent to indicate that a system is functioning properly. In a replication context, if the source stops sending such messages, one of the replicas can take its place. Similar techniques can be used between the servers in a cluster environment, to confirm that all of them are operating properly.

另请参见 复制，源。See Also replication, source.

表示上限的值，可以是运行时不应超过的硬性上限，也可以是实际达到的最大值的记录。与低水位标记形成对比。 A value representing an upper limit, either a hard limit that should not be exceeded at runtime, or a record of the maximum value that was actually reached. Contrast with low-water mark.

另请参见 低水位标记。See Also low-water mark.

有一份 事务 列表，其中包含计划由 InnoDB 清除 操作处理的已标记删除的记录。记录在 撤销日志 中。历史列表的长度由命令 SHOW ENGINE INNODB STATUS 报告。如果历史列表长度超过 innodb_max_purge_lag 配置选项的值，每个 DML 操作会稍微延迟，以允许清除操作完成 刷新 已删除的记录。 A list of transactions with delete-marked records scheduled to be processed by the InnoDB purge operation. Recorded in the undo log. The length of the history list is reported by the command SHOW ENGINE INNODB STATUS. If the history list grows longer than the value of the innodb_max_purge_lag configuration option, each DML operation is delayed slightly to allow the purge operation to finish flushing the deleted records.

也称为 清除延迟。Also known as purge lag.

另请参见 DML、刷新（flush）、清除（purge）、清除延迟（purge lag）、回滚段（rollback segment）、事务（transaction）、回滚日志（undo log）。See Also DML, flush, purge, purge lag, rollback segment, transaction, undo log.

从页面释放空块。InnoDB 透明页面压缩 功能依赖于孔打支持。欲了解更多信息，请参见 第 17.9.2 节，“InnoDB 页面压缩”。 Releasing empty blocks from a page. The InnoDB transparent page compression feature relies on hole punching support. For more information, see Section 17.9.2, “InnoDB Page Compression”.

另请参阅 稀疏文件，透明页面压缩。See Also sparse file, transparent page compression.

数据库服务器的网络名称，用于建立连接。通常与端口一起指定。在某些情况下，IP 地址127.0.0.1比特殊名称localhost更适合访问与应用程序在同一服务器上的数据库。 The network name of a database server, used to establish a connection. Often specified in conjunction with a port. In some contexts, the IP address 127.0.0.1 works better than the special name localhost for accessing a database on the same server as the application.

另请参见 连接、localhost、端口。See Also connection, localhost, port.

一种情况，其中某行、表或内部数据结构被访问得非常频繁，需要某种形式的锁定或互斥，从而导致性能或可扩展性问题。 A condition where a row, table, or internal data structure is accessed so frequently, requiring some form of locking or mutual exclusion, that it results in a performance or scalability issue.

虽然“热”通常表示一个不希望出现的情况，但热备份是首选的备份类型。Although “hot” typically indicates an undesirable condition, a hot backup is the preferred type of backup.

另请参见 热备份。See Also hot backup.

当数据库正在运行且应用程序正在对其进行读写操作时所进行的备份。备份不仅仅是简单地复制数据文件：它必须包括备份过程中插入或更新的任何数据；必须排除备份过程中删除的任何数据；并且必须忽略任何未提交的更改。 A backup taken while the database is running and applications are reading and writing to it. The backup involves more than simply copying data files: it must include any data that was inserted or updated while the backup was in process; it must exclude any data that was deleted while the backup was in process; and it must ignore any changes that were not committed.

执行热备份的 Oracle 产品，尤其是针对 InnoDB 表，同时也适用于 MyISAM 表和其他存储引擎的表，被称为 MySQL 企业备份。The Oracle product that performs hot backups, of InnoDB tables especially but also tables from MyISAM and other storage engines, is known as MySQL Enterprise Backup.

热备份过程包括两个阶段。初始的数据文件复制会生成一个 原始备份。应用 步骤会合并备份运行期间数据库发生的任何变化。应用这些变化会生成一个 准备好的 备份；这些文件随时可以恢复。The hot backup process consists of two stages. The initial copying of the data files produces a raw backup. The apply step incorporates any changes to the database that happened while the backup was running. Applying the changes produces a prepared backup; these files are ready to be restored whenever necessary.

另见 应用, MySQL 企业备份, 准备好的备份, 原始备份。See Also apply, MySQL Enterprise Backup, prepared backup, raw backup.

每表文件表空间 和一般表空间的数据文件。每表文件表空间 .ibd 文件包含单个表及其关联的索引数据。一般表空间 .ibd 文件可能包含多个表的表和索引数据。 The data file for file-per-table tablespaces and general tablespaces. File-per-table tablespace .ibd files contain a single table and associated index data. General tablespace .ibd files may contain table and index data for multiple tables.

.ibd 文件扩展名不适用于系统表空间，系统表空间由一个或多个ibdata 文件组成。The .ibd file extension does not apply to the system tablespace, which consists of one or more ibdata files.

如果使用 DATA DIRECTORY = 子句创建了每表文件表空间或一般表空间，.ibd 文件将位于指定路径，而不是在普通数据目录内。If a file-per-table tablespace or general tablespace is created with the DATA DIRECTORY = clause, the .ibd file is located at the specified path, outside the normal data directory.

当 .ibd 文件被 MySQL 企业备份 产品包含在压缩备份中时，压缩后的文件对应为 .ibz 文件。When a .ibd file is included in a compressed backup by the MySQL Enterprise Backup product, the compressed equivalent is a .ibz file.

另见 数据库，每表文件，通用表空间，ibdata 文件，.ibz 文件，innodb_file_per_table，MySQL 企业备份，系统表空间。See Also database, file-per-table, general tablespace, ibdata file, .ibz file, innodb_file_per_table, MySQL Enterprise Backup, system tablespace.

当 MySQL 企业备份 产品执行 压缩备份 时，它会将使用 每表文件 设置创建的每个 表空间 文件的扩展名从 .ibd 转换为 .ibz。 When the MySQL Enterprise Backup product performs a compressed backup, it transforms each tablespace file that is created using the file-per-table setting from a .ibd extension to a .ibz extension.

在备份期间应用的压缩不同于在正常操作期间保持表数据压缩的 压缩行格式。对于已经使用压缩行格式的表空间，压缩备份操作会跳过压缩步骤，因为再次压缩会减慢备份速度，但几乎不会或根本不会节省空间。The compression applied during backup is distinct from the compressed row format that keeps table data compressed during normal operation. A compressed backup operation skips the compression step for a tablespace that is already in compressed row format, as compressing a second time would slow down the backup but produce little or no space savings.

参见 压缩备份、压缩行格式、每表文件、.ibd 文件、MySQL 企业备份、表空间。See Also compressed backup, compressed row format, file-per-table, .ibd file, MySQL Enterprise Backup, tablespace.

由 InnoDB 在 MySQL 数据库中管理的一组文件：系统表空间、每表文件表空间 文件，以及 重做日志 文件。根据 MySQL 版本和 InnoDB 配置，也可能包括 通用表空间、临时表空间 和 撤销表空间 文件。该术语有时在讨论 InnoDB 文件结构和格式的详细内容时使用，用以指代由 InnoDB 在 MySQL 数据库中管理的文件集合。 The set of files managed by InnoDB within a MySQL database: the system tablespace, file-per-table tablespace files, and redo log files. Depending on MySQL version and InnoDB configuration, may also include general tablespace, temporary tablespace, and undo tablespace files. This term is sometimes used in detailed discussions of InnoDB file structures and formats to refer to the set of files managed by InnoDB within a MySQL database.

另请参阅 数据库、每表文件、通用表空间、重做日志、系统表空间、临时表空间、回滚表空间。See Also database, file-per-table, general tablespace, redo log, system tablespace, temporary tablespace, undo tablespace.

由 MySQL 企业备份 产品在 热备份 操作期间创建的补充备份文件。它包含在备份运行期间发生的任何数据更改的信息。初始备份文件，包括 ibbackup_logfile，被称为 原始备份，因为备份操作期间发生的更改尚未合并。执行 应用 步骤到原始备份文件后，生成的文件确实包含了最终的数据更改，并被称为 已准备备份。在此阶段，ibbackup_logfile 文件不再是必需的。 A supplemental backup file created by the MySQL Enterprise Backup product during a hot backup operation. It contains information about any data changes that occurred while the backup was running. The initial backup files, including ibbackup_logfile, are known as a raw backup, because the changes that occurred during the backup operation are not yet incorporated. After you perform the apply step to the raw backup files, the resulting files do include those final data changes, and are known as a prepared backup. At this stage, the ibbackup_logfile file is no longer necessary.

另请参见 应用、热备份、MySQL 企业备份、准备备份、原始备份。See Also apply, hot backup, MySQL Enterprise Backup, prepared backup, raw backup.

一组文件，名称如 ibdata1、ibdata2 等，它们组成了 InnoDB 系统表空间。有关系统表空间 ibdata 文件中所包含的结构和数据的信息，请参见 第 17.6.3.1 节，“系统表空间”。 A set of files with names such as ibdata1, ibdata2, and so on, that make up the InnoDB system tablespace. For information about the structures and data that reside in the system tablespace ibdata files, see Section 17.6.3.1, “The System Tablespace”.

ibdata 文件的增长受到 innodb_autoextend_increment 配置选项的影响。Growth of the ibdata files is influenced by the innodb_autoextend_increment configuration option.

参见 更改缓冲区、数据字典、双写缓冲区、每表文件、.ibd 文件、innodb_file_per_table、系统表空间、撤销日志。See Also change buffer, data dictionary, doublewrite buffer, file-per-table, .ibd file, innodb_file_per_table, system tablespace, undo log.

用于非压缩 InnoDB 临时表 及相关对象的 InnoDB 临时表空间 数据文件。配置文件选项 innodb_temp_data_file_path 允许用户定义临时表空间数据文件的相对路径。如果未指定 innodb_temp_data_file_path，默认行为是在数据目录中创建一个名为 ibtmp1 的 12MB 自动扩展数据文件，与 ibdata1 并列。 The InnoDB temporary tablespace data file for non-compressed InnoDB temporary tables and related objects. The configuration file option, innodb_temp_data_file_path, allows users to define a relative path for the temporary tablespace data file. If innodb_temp_data_file_path is not specified, the default behavior is to create a single auto-extending 12MB data file named ibtmp1 in the data directory, alongside ibdata1.

另请参阅 数据文件、临时表、临时表空间。See Also data files, temporary table, temporary tablespace.

一组文件，通常命名为 ib_logfile0 和 ib_logfile1，组成了 重做日志。有时也称为 日志组。这些文件记录尝试更改 InnoDB 表中数据的语句。在崩溃后启动时，这些语句会被自动重放，以纠正未完成事务写入的数据。 A set of files, typically named ib_logfile0 and ib_logfile1, that form the redo log. Also sometimes referred to as the log group. These files record statements that attempt to change data in InnoDB tables. These statements are replayed automatically to correct data written by incomplete transactions, on startup following a crash.

这些数据不能用于手动恢复；对于这种类型的操作，请使用 二进制日志。This data cannot be used for manual recovery; for that type of operation, use the binary log.

另请参见 二进制日志、日志组、重做日志。See Also binary log, log group, redo log.

在 InnoDB 全文索引 中，由文档 ID 和标记的位置信息（即特定单词）组成的数据结构。 Within an InnoDB FULLTEXT index, the data structure consisting of a document ID and positional information for a token (that is, a particular word).

另请参见 FULLTEXT 索引。See Also FULLTEXT index.

A row lock that InnoDB acquires to ensure consistency, without you specifically requesting it.

参见 行锁。See Also row lock.

一种将数据保存在内存中的数据库系统，以避免由于磁盘 I/O 和磁盘块与内存区域之间转换造成的开销。一些内存数据库会牺牲持久性（“D” 在 ACID 设计理念中）并容易受到硬件、电源及其他类型故障的影响，因此更适合只读操作。其他内存数据库则使用持久性机制，例如将更改记录到磁盘或使用非易失性内存。 A type of database system that maintains data in memory, to avoid overhead due to disk I/O and translation between disk blocks and memory areas. Some in-memory databases sacrifice durability (the “D” in the ACID design philosophy) and are vulnerable to hardware, power, and other types of failures, making them more suitable for read-only operations. Other in-memory databases do use durability mechanisms such as logging changes to disk or using non-volatile memory.

MySQL 处理同类型内存密集型操作的功能包括 InnoDB 缓冲池、自适应哈希索引 和 只读事务 优化，MEMORY 存储引擎、MyISAM 键缓存，以及 MySQL 查询缓存。MySQL features that address the same kinds of memory-intensive processing include the InnoDB buffer pool, adaptive hash index, and read-only transaction optimization, the MEMORY storage engine, the MyISAM key cache, and the MySQL query cache.

另请参见 ACID，自适应哈希索引，缓冲池，基于磁盘，只读事务。See Also ACID, adaptive hash index, buffer pool, disk-based, read-only transaction.

一种由 MySQL 企业备份 产品执行的 热备份 类型，它只保存自某个时间点以来发生更改的数据。拥有完整备份和一系列增量备份可以让您在较长时间内重建备份数据，而无需保留多个完整备份所带来的存储开销。您可以先恢复完整备份，然后依次应用每个增量备份，或者通过将每个增量备份应用到完整备份中，使其保持最新状态，然后执行一次恢复操作。 A type of hot backup, performed by the MySQL Enterprise Backup product, that only saves data changed since some point in time. Having a full backup and a succession of incremental backups lets you reconstruct backup data over a long period, without the storage overhead of keeping several full backups on hand. You can restore the full backup and then apply each of the incremental backups in succession, or you can keep the full backup up-to-date by applying each incremental backup to it, then perform a single restore operation.

更改数据的粒度为 页 级别。一个页实际上可能包含多行。每个更改的页都会包含在备份中。The granularity of changed data is at the page level. A page might actually cover more than one row. Each changed page is included in the backup.

另请参见 热备份、MySQL 企业备份、页。See Also hot backup, MySQL Enterprise Backup, page.

一种数据结构，为 表的 行 提供快速查找能力，通常通过形成一个树结构 (B 树) 来表示某一 列 或若干列的所有值。 A data structure that provides a fast lookup capability for rows of a table, typically by forming a tree structure (B-tree) representing all the values of a particular column or set of columns.

InnoDB 表总是有一个 聚簇索引 来表示 主键。它们还可以在一个或多个列上定义一个或多个 二级索引。根据其结构，二级索引可以被分类为 部分、列 或 复合 索引。InnoDB tables always have a clustered index representing the primary key. They can also have one or more secondary indexes defined on one or more columns. Depending on their structure, secondary indexes can be classified as partial, column, or composite indexes.

索引是查询性能的关键方面。数据库架构师设计表、查询和索引，以便应用程序所需的数据可以快速查找。理想的数据库设计在可行的情况下使用覆盖索引；查询结果完全从索引计算，而不读取实际的表数据。每个外键约束也需要一个索引，以便高效地检查值是否同时存在于父表和子表中。Indexes are a crucial aspect of query performance. Database architects design tables, queries, and indexes to allow fast lookups for data needed by applications. The ideal database design uses a covering index where practical; the query results are computed entirely from the index, without reading the actual table data. Each foreign key constraint also requires an index, to efficiently check whether values exist in both the parent and child tables.

虽然 B 树索引是最常见的，但对于 哈希索引，使用的是不同类型的数据结构，例如在 MEMORY 存储引擎和 InnoDB 自适应哈希索引 中。R 树 索引用于多维信息的空间索引。Although a B-tree index is the most common, a different kind of data structure is used for hash indexes, as in the MEMORY storage engine and the InnoDB adaptive hash index. R-tree indexes are used for spatial indexing of multi-dimensional information.

另请参见 自适应哈希索引、B 树、子表、聚簇索引、列索引、复合索引、覆盖索引、外键、哈希索引、父表、部分索引、主键、查询、R 树、行、二级索引、表。See Also adaptive hash index, B-tree, child table, clustered index, column index, composite index, covering index, foreign key, hash index, parent table, partial index, primary key, query, R-tree, row, secondary index, table.

一个内存区域，用于保存 InnoDB 全文搜索 的分词数据。它缓冲数据，以在向属于 FULLTEXT 索引 的列中插入或更新数据时尽量减少磁盘 I/O。当索引缓存变满时，分词数据会写入磁盘。每个 InnoDB FULLTEXT 索引都有自己的独立索引缓存，其大小由配置选项 innodb_ft_cache_size 控制。 A memory area that holds the token data for InnoDB full-text search. It buffers the data to minimize disk I/O when data is inserted or updated in columns that are part of a FULLTEXT index. The token data is written to disk when the index cache becomes full. Each InnoDB FULLTEXT index has its own separate index cache, whose size is controlled by the configuration option innodb_ft_cache_size.

另请参见 全文搜索，FULLTEXT 索引。See Also full-text search, FULLTEXT index.

索引条件下推（ICP）是一种优化技术，如果条件的一部分可以使用索引中的字段进行评估，就会将 WHERE 条件的部分内容下推到存储引擎。ICP 可以减少 存储引擎 访问基表的次数，以及 MySQL 服务器访问存储引擎的次数。更多信息，请参见 第 10.2.1.6 节，“索引条件下推优化”。 Index condition pushdown (ICP) is an optimization that pushes part of a WHERE condition down to the storage engine if parts of the condition can be evaluated using fields from the index. ICP can reduce the number of times the storage engine must access the base table and the number of times the MySQL server must access the storage engine. For more information, see Section 10.2.1.6, “Index Condition Pushdown Optimization”.

另见 索引，存储引擎。See Also index, storage engine.