怎么在MySQL中查看使用的内存？针对这个问题，这篇文章详细介绍了相对应的分析和解答，希望可以帮助更多想解决这个问题的小伙伴找到更简单易行的方法。

performance_schema有如下表记录内存使用情况

mysql>showtableslike'%memory%summary%';+-------------------------------------------------+|Tables_in_performance_schema(%memory%summary%)|+-------------------------------------------------+|memory_summary_by_account_by_event_name||memory_summary_by_host_by_event_name||memory_summary_by_thread_by_event_name||memory_summary_by_user_by_event_name||memory_summary_global_by_event_name|+-------------------------------------------------+

每个内存统计表都有如下统计列：

* COUNT_ALLOC，COUNT_FREE：对内存分配和释放内存函数的调用总次数

* SUM_NUMBER_OF_BYTES_ALLOC，SUM_NUMBER_OF_BYTES_FREE：已分配和已释放的内存块的总字节大小

* CURRENT_COUNT_USED：这是一个便捷列，等于COUNT_ALLOC - COUNT_FREE

* CURRENT_NUMBER_OF_BYTES_USED：当前已分配的内存块但未释放的统计大小。这是一个便捷列，等于SUM_NUMBER_OF_BYTES_ALLOC - SUM_NUMBER_OF_BYTES_FREE

* LOW_COUNT_USED，HIGH_COUNT_USED：对应CURRENT_COUNT_USED列的低和高水位标记

* LOW_NUMBER_OF_BYTES_USED，HIGH_NUMBER_OF_BYTES_USED：对应CURRENT_NUMBER_OF_BYTES_USED列的低和高水位标记

内存统计表允许使用TRUNCATE TABLE语句。使用truncate语句时有如下行为：

* 通常，truncate操作会重置统计信息的基准数据（即清空之前的数据），但不会修改当前server的内存分配等状态。也就是说，truncate内存统计表不会释放已分配内存

* 将COUNT_ALLOC和COUNT_FREE列重置，并重新开始计数（等于内存统计信息以重置后的数值作为基准数据）

* SUM_NUMBER_OF_BYTES_ALLOC和SUM_NUMBER_OF_BYTES_FREE列重置与COUNT_ALLOC和COUNT_FREE列重置类似

* LOW_COUNT_USED和HIGH_COUNT_USED将重置为CURRENT_COUNT_USED列值

* LOW_NUMBER_OF_BYTES_USED和HIGH_NUMBER_OF_BYTES_USED将重置为CURRENT_NUMBER_OF_BYTES_USED列值

* 此外，按照帐户，主机，用户或线程分类统计的内存统计表或memory_summary_global_by_event_name表，如果在对其依赖的accounts、hosts、users表执行truncate时，会隐式对这些内存统计表执行truncate语句

简单来说，就是可以根据用户、主机、线程、账号、全局的维度对内存进行监控。同时库sys也就这些表做了进一步的格式化，可以使得用户非常容易的观察到每个对象的内存开销：

mysql>selectevent_name,current_allocfromsys.memory_global_by_current_byteslimit10;+-----------------------------------------------------------------------------+---------------+|event_name|current_alloc|+-----------------------------------------------------------------------------+---------------+|memory/performance_schema/events_statements_history_long|13.66MiB||memory/performance_schema/events_statements_history_long.sqltext|9.77MiB||memory/performance_schema/events_statements_history_long.tokens|9.77MiB||memory/performance_schema/events_statements_summary_by_digest.tokens|9.77MiB||memory/performance_schema/table_handles|9.06MiB||memory/performance_schema/events_statements_summary_by_thread_by_event_name|8.67MiB||memory/sql/String::value|6.02MiB||memory/performance_schema/memory_summary_by_thread_by_event_name|5.62MiB||memory/performance_schema/events_statements_summary_by_digest|4.88MiB||memory/sql/TABLE|4.35MiB|+-----------------------------------------------------------------------------+---------------+

默认情况下performance_schema只对performance_schema进行了内存开销的统计。根据你的MySQL安装代码区域可能包括performance_schema、sql、client、innodb、myisam、csv、memory、blackhole、archive、partition和其他。

查看innodb相关的内存监控是否开启，默认不开启

mysql>SELECT*FROMperformance_schema.setup_instruments->WHERENAMELIKE'%memory%';

+--------------------------------------------------------------------------------+---------+-------+|NAME|ENABLED|TIMED|+--------------------------------------------------------------------------------+---------+-------+|memory/performance_schema/mutex_instances|YES|NO||memory/performance_schema/rwlock_instances|YES|NO||memory/performance_schema/cond_instances|YES|NO||memory/performance_schema/file_instances|YES|NO||memory/performance_schema/socket_instances|YES|NO||memory/performance_schema/metadata_locks|YES|NO||memory/performance_schema/file_handle|YES|NO||memory/performance_schema/accounts|YES|NO||memory/performance_schema/events_waits_summary_by_account_by_event_name|YES|NO||memory/performance_schema/events_stages_summary_by_account_by_event_name|YES|NO||memory/performance_schema/events_statements_summary_by_account_by_event_name|YES|NO||memory/performance_schema/events_transactions_summary_by_account_by_event_name|YES|NO||memory/performance_schema/memory_summary_by_account_by_event_name|YES|NO||memory/performance_schema/events_stages_summary_global_by_event_name|YES|NO||memory/performance_schema/events_statements_summary_global_by_event_name|YES|NO||memory/performance_schema/memory_summary_global_by_event_name|YES|NO||memory/performance_schema/hosts|YES|NO||memory/performance_schema/events_waits_summary_by_host_by_event_name|YES|NO||memory/performance_schema/events_stages_summary_by_host_by_event_name|YES|NO||memory/performance_schema/events_statements_summary_by_host_by_event_name|YES|NO||memory/performance_schema/events_transactions_summary_by_host_by_event_name|YES|NO|

可以通过条件缩小范围：

mysql>SELECT*FROMperformance_schema.setup_instrumentsWHERENAMELIKE'%memory/innodb%';+-------------------------------------------+---------+-------+|NAME|ENABLED|TIMED|+-------------------------------------------+---------+-------+|memory/innodb/adaptivehashindex|NO|NO||memory/innodb/buf_buf_pool|NO|NO||memory/innodb/dict_stats_bg_recalc_pool_t|NO|NO||memory/innodb/dict_stats_index_map_t|NO|NO||memory/innodb/dict_stats_n_diff_on_level|NO|NO||memory/innodb/other|NO|NO||memory/innodb/row_log_buf|NO|NO||memory/innodb/row_merge_sort|NO|NO||memory/innodb/std|NO|NO||memory/innodb/trx_sys_t::rw_trx_ids|NO|NO|

对所有可能的对象进行内存监控。因此，还需要做下面的设置：

mysql>updateperformance_schema.setup_instrumentssetenabled='yes'wherenamelike'memory%';QueryOK,306rowsaffected(0.00sec)Rowsmatched:376Changed:306Warnings:0

但是这种在线打开内存统计的方法仅对之后新增的内存对象有效，重启数据库后又会还原设置：

如想要对全局生命周期中的对象进行内存统计，必须在配置文件中进行设置，然后重启：

[mysqld]performance-schema-instrument='memory/%=COUNTED'

可以使用sys库下的memory_global_by_current_bytes表来查询相同的底层数据，该模式表显示了全局服务器内当前内存使用情况，按分配类型进行细分。

mysql>SELECT*FROMsys.memory_global_by_current_bytesWHEREevent_nameLIKE'memory/innodb/buf_buf_pool'\G***************************1.row***************************event_name:memory/innodb/buf_buf_poolcurrent_count:1current_alloc:131.06MiBcurrent_avg_alloc:131.06MiBhigh_count:1high_alloc:131.06MiBhigh_avg_alloc:131.06MiB

此sys模式查询通过current_alloc()代码区域聚合当前分配的内存：

mysql>SELECTSUBSTRING_INDEX(event_name,'/',2)AScode_area,sys.format_bytes(SUM(current_alloc))AScurrent_allocFROMsys.x$memory_global_by_current_bytesGROUPBYSUBSTRING_INDEX(event_name,'/',2)ORDERBYSUM(current_alloc)DESC;+---------------------------+---------------+|code_area|current_alloc|+---------------------------+---------------+|memory/innodb|843.24MiB||memory/performance_schema|81.29MiB||memory/mysys|8.20MiB||memory/sql|2.47MiB||memory/memory|174.01KiB||memory/myisam|46.53KiB||memory/blackhole|512bytes||memory/federated|512bytes||memory/csv|512bytes||memory/vio|496bytes|+---------------------------+---------------+

关于怎么在MySQL中查看使用的内存问题的解答就分享到这里了，希望以上内容可以对大家有一定的帮助，如果你还有很多疑惑没有解开，可以关注亿速云行业资讯频道了解更多相关知识。