MySQL 8.4 Release Notes
- 16.1 数据字典模式16.1 Data Dictionary Schema
- 16.2 基于文件的元数据存储移除16.2 Removal of File-based Metadata Storage
- 16.3 字典数据的事务性存储16.3 Transactional Storage of Dictionary Data
- 16.4 字典对象缓存16.4 Dictionary Object Cache
- 16.5 INFORMATION_SCHEMA 与数据字典集成16.5 INFORMATION_SCHEMA and Data Dictionary Integration
- 16.6 序列化字典信息（SDI）16.6 Serialized Dictionary Information (SDI)
- 16.7 数据字典使用差异16.7 Data Dictionary Usage Differences
- 16.8 数据字典限制16.8 Data Dictionary Limitations
Server 集成了一个事务式数据字典，用于存储数据库对象的信息。在之前的 MySQL 版本中，字典数据存储在元数据文件、非事务表和存储引擎专用数据字典中。MySQL Server incorporates a transactional data dictionary that stores information about database objects. In previous MySQL releases, dictionary data was stored in metadata files, nontransactional tables, and storage engine-specific data dictionaries.
本章描述了数据字典的主要特性、优点、使用差异和限制。关于数据字典功能的其他内容，请参阅 “数据字典说明” 部分，位于 MySQL 8.4 发行说明 中。This chapter describes the main features, benefits, usage differences, and limitations of the data dictionary. For other implications of the data dictionary feature, refer to the “Data Dictionary Notes” section in the MySQL 8.4 Release Notes.
MySQL 数据字典的优点包括：Benefits of the MySQL data dictionary include:
集中式数据字典模式的简便性，它统一存储字典数据。参见 第 16.1 节，“数据字典模式”。Simplicity of a centralized data dictionary schema that uniformly stores dictionary data. See Section 16.1, “Data Dictionary Schema”.
删除基于文件的元数据存储。参见 第 16.2 节，“删除基于文件的元数据存储”。Removal of file-based metadata storage. See Section 16.2, “Removal of File-based Metadata Storage”.
字典数据的事务性、崩溃安全存储。参见 第 16.3 节，“字典数据的事务性存储”。Transactional, crash-safe storage of dictionary data. See Section 16.3, “Transactional Storage of Dictionary Data”.
字典对象的统一和集中缓存。参见 第 16.4 节，“字典对象缓存”。Uniform and centralized caching for dictionary objects. See Section 16.4, “Dictionary Object Cache”.
一些
INFORMATION_SCHEMA表的更简单且改进的实现。参见 第 16.5 节，“INFORMATION_SCHEMA 与数据字典的整合”。A simpler and improved implementation for someINFORMATION_SCHEMAtables. See Section 16.5, “INFORMATION_SCHEMA and Data Dictionary Integration”.原子 DDL。参见 第 15.1.1 节，“原子数据定义语句支持”。Atomic DDL. See Section 15.1.1, “Atomic Data Definition Statement Support”.
Important
启用数据字典的服务器与未启用数据字典的服务器在一般操作上存在一些差异；参见 第 16.7 节，“数据字典使用差异”。另外，对于升级到 MySQL 8.0，升级过程相较于以前的 MySQL 版本有所不同，并且需要通过检查特定的先决条件来验证安装包的升级准备情况。有关更多信息，请参见 第 3 章，升级 MySQL，特别是 第 3.6 节，“升级前准备安装”。A data dictionary-enabled server entails some general operational differences compared to a server that does not have a data dictionary; see Section 16.7, “Data Dictionary Usage Differences”. Also, for upgrades to MySQL 8.0, the upgrade procedure differs somewhat from previous MySQL releases and requires that you verify the upgrade readiness of your installation by checking specific prerequisites. For more information, see Chapter 3, Upgrading MySQL, particularly Section 3.6, “Preparing Your Installation for Upgrade”.