在 MySQL 使用过程中，偶尔会出现OOM、内存异常突增等异常现象。为了排查内存异常，我们需要分析内存占用情况，找出内存占用的具体事件。我们可以从以下几张performance下的表分析内存，每张表对应不同的维度，有用户维度、主机维度、进程维度。为了打开 performance_schema 功能，我们需要在 MySQL 配置中设置 performance_schema = ON。

#每张表对应不同的维度，有用户维度、主机维度、进程维度。我们需要在 MySQL 配置中设置 performance_schema = ON。root@mysql 21:46:  [performance_schema]> show tables like '%mem%';
+-----------------------------------------+
| Tables_in_performance_schema (%mem%)    |
+-----------------------------------------+
| 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     |
| replication_group_member_stats          |
| replication_group_members               |
+-----------------------------------------+
7 rows in set (0.00 sec)#查看 MySQL 总消耗内存root@mysql 21:48:  [performance_schema]> select * from sys.memory_global_total;
+-----------------+
| total_allocated |
+-----------------+
| 1.32 GiB        |
+-----------------+
1 row in set (0.00 sec)#查看总体内存占用情况root@mysql 21:48:  [performance_schema]> select event_name,CURRENT_NUMBER_OF_BYTES_USED/1024/1024 from performance_schema.memory_summary_global_by_event_name order by CURRENT_NUMBER_OF_BYTES_USED desc LIMIT 20; 
+------------------------------------------------------------------------------+----------------------------------------+
| event_name                                                                   | CURRENT_NUMBER_OF_BYTES_USED/1024/1024 |
+------------------------------------------------------------------------------+----------------------------------------+
| memory/innodb/buf_buf_pool                                                   |                          1048.50000000 |
| memory/innodb/log0log                                                        |                            64.00839996 |
| memory/mysys/KEY_CACHE                                                       |                            32.00141907 |
| memory/innodb/hash0hash                                                      |                            31.70213318 |
| memory/innodb/os0event                                                       |                            25.56757355 |
| memory/performance_schema/events_statements_history_long                     |                            13.65661621 |
| memory/performance_schema/events_statements_summary_by_digest.tokens         |                             9.76562500 |
| memory/performance_schema/events_statements_history_long.sqltext             |                             9.76562500 |
| memory/performance_schema/events_statements_history_long.tokens              |                             9.76562500 |
| memory/performance_schema/events_statements_summary_by_thread_by_event_name  |                             8.66992188 |
| memory/performance_schema/memory_summary_by_thread_by_event_name             |                             5.62500000 |
| memory/performance_schema/events_statements_summary_by_digest                |                             4.88281250 |
| memory/performance_schema/events_statements_summary_by_account_by_event_name |                             4.33496094 |
| memory/performance_schema/events_statements_summary_by_user_by_event_name    |                             4.33496094 |
| memory/performance_schema/events_statements_summary_by_host_by_event_name    |                             4.33496094 |
| memory/innodb/ut0pool                                                        |                             4.00016785 |
| memory/performance_schema/table_shares                                       |                             4.00000000 |
| memory/performance_schema/events_statements_history                          |                             3.49609375 |
| memory/performance_schema/events_statements_current                          |                             3.49609375 |
| memory/performance_schema/events_waits_summary_by_thread_by_event_name       |                             3.39062500 |
+------------------------------------------------------------------------------+----------------------------------------+
20 rows in set (0.00 sec)#查看线程内存占用情况root@mysql 21:51:  [performance_schema]> select thread_id,event_name,CURRENT_NUMBER_OF_BYTES_USED/1024/1024 from performance_schema.memory_summary_by_thread_by_event_name order by CURRENT_NUMBER_OF_BYTES_USED desc limit 10;
+-----------+----------------------------+----------------------------------------+
| thread_id | event_name                 | CURRENT_NUMBER_OF_BYTES_USED/1024/1024 |
+-----------+----------------------------+----------------------------------------+
|         1 | memory/innodb/buf_buf_pool |                          1048.50000000 |
|         1 | memory/innodb/log0log      |                            64.00839996 |
|         1 | memory/mysys/KEY_CACHE     |                            32.00141907 |
|         1 | memory/innodb/hash0hash    |                            31.70213318 |
|         1 | memory/innodb/os0event     |                            25.56420135 |
|         1 | memory/innodb/ut0pool      |                             4.00016785 |
|         1 | memory/innodb/os0file      |                             2.60424805 |
|         1 | memory/innodb/buf0dblwr    |                             2.01696014 |
|         1 | memory/innodb/mem0mem      |                             0.34970760 |
|         1 | memory/innodb/lock0lock    |                             0.23637390 |
+-----------+----------------------------+----------------------------------------+
10 rows in set (0.00 sec)