INSERT、UPDATE 和 DELETE 操作可能会修改二级索引。如果受影响的索引页不在缓冲池中，修改可以缓存在更改缓冲中。INSERT, UPDATE, and DELETE operations can modify secondary indexes. If an affected index page is not in the buffer pool, the changes can be buffered in the change buffer.

当辅助索引页不在缓冲池中时，对辅助索引的更改进行缓冲，可以避免立即从磁盘读取受影响索引页所需的昂贵随机访问 I/O 操作。缓冲的更改可以稍后以批量方式应用，当页面通过其他读取操作被读入缓冲池时。Buffering secondary index changes when secondary index pages are not in the buffer pool avoids expensive random access I/O operations that would be required to immediately read in affected index pages from disk. Buffered changes can be applied later, in batches, as pages are read into the buffer pool by other read operations.

不支持。更改缓冲只支持辅助索引。聚簇索引、全文索引和空间索引不支持。全文索引有其自己的缓存机制。No. The change buffer only supports secondary indexes. Clustered indexes, full-text indexes, and spatial indexes are not supported. Full-text indexes have their own caching mechanism.

在 MySQL 5.6 引入 innodb_change_buffer_max_size 配置选项之前，系统表空间中磁盘上的更改缓冲区的最大大小是 InnoDB 缓冲池大小的 1/3。Prior to the introduction of the innodb_change_buffer_max_size configuration option in MySQL 5.6, the maximum size of the on-disk change buffer in the system tablespace was 1/3 of the InnoDB buffer pool size.

在 MySQL 5.6 及更高版本中，innodb_change_buffer_max_size 配置选项定义了更改缓冲区的最大大小，占总缓冲池大小的百分比。默认情况下，innodb_change_buffer_max_size 设置为 25。最大设置为 50。In MySQL 5.6 and later, the innodb_change_buffer_max_size configuration option defines the maximum size of the change buffer as a percentage of the total buffer pool size. By default, innodb_change_buffer_max_size is set to 25. The maximum setting is 50.

InnoDB 如果操作会导致磁盘上的更改缓冲区超过定义的限制，则不会缓冲该操作。InnoDB does not buffer an operation if it would cause the on-disk change buffer to exceed the defined limit.

更改缓冲页面不需要在缓冲池中持久存在，并且可能会被 LRU 操作驱逐。Change buffer pages are not required to persist in the buffer pool and may be evicted by LRU operations.

更改缓冲区的当前大小可以通过 SHOW ENGINE INNODB STATUS \G 查看，在 INSERT BUFFER AND ADAPTIVE HASH INDEX 章节下。例如：The current size of the change buffer is reported by SHOW ENGINE INNODB STATUS \G, under the INSERT BUFFER AND ADAPTIVE HASH INDEX heading. For example:

-------------------------------------
INSERT BUFFER AND ADAPTIVE HASH INDEX
-------------------------------------
Ibuf: size 1, free list len 0, seg size 2, 0 merges

相关的数据点包括：Relevant data points include:

有关监控更改缓冲区状态的信息，请参见 第 17.5.2 节，“更改缓冲区”。For information about monitoring change buffer status, see Section 17.5.2, “Change Buffer”.

更新的页面通过刷新机制刷新，该机制同样会刷新占用缓冲池的其他页面。Updated pages are flushed by the same flushing mechanism that flushes the other pages that occupy the buffer pool.

变更缓冲区是一个旨在减少对二级索引的随机 I/O 的功能，当索引变得越来越大且不再适合 InnoDB 缓冲池时特别有用。通常，当整个数据集无法装入缓冲池、存在大量修改二级索引页的 DML 活动，或存在许多经常被 DML 操作修改的二级索引时，应该使用变更缓冲区。The change buffer is a feature designed to reduce random I/O to secondary indexes as indexes grow larger and no longer fit in the InnoDB buffer pool. Generally, the change buffer should be used when the entire data set does not fit into the buffer pool, when there is substantial DML activity that modifies secondary index pages, or when there are lots of secondary indexes that are regularly changed by DML activity.

如果整个数据集可以容纳在InnoDB缓冲池中，如果您只有相对较少的二级索引，或者如果您使用的是固态存储（随机读取速度几乎与顺序读取一样快），您可以考虑禁用更改缓冲区。在进行配置更改之前，建议您使用代表性工作负载进行测试，以确定禁用更改缓冲区是否带来任何好处。You might consider disabling the change buffer if the entire data set fits within the InnoDB buffer pool, if you have relatively few secondary indexes, or if you are using solid-state storage, where random reads are about as fast as sequential reads. Before making configuration changes, it is recommended that you run tests using a representative workload to determine if disabling the change buffer provides any benefit.

请参见第 17.5.2 节，“更改缓冲区”。See Section 17.5.2, “Change Buffer”.