8.12.4.2 Monitoring MySQL Memory Usage

The following example demonstrates how to use Performance Schema and sys schema to monitor MySQL memory usage.

Most Performance Schema memory instrumentation is disabled by default. Instruments can be enabled by updating the ENABLED column of the Performance Schema setup_instruments table. Memory instruments have names in the form of memory/code_area/instrument_name, where code_area is a value such as sql or innodb, and instrument_name is the instrument detail.

1. To view available MySQL memory instruments, query the Performance Schema setup_instruments table. The following query returns hundreds of memory instruments for all code areas.

   mysql> SELECT * FROM performance_schema.setup_instruments
          WHERE NAME LIKE '%memory%';

   You can narrow results by specifying a code area. For example, you can limit results to InnoDB memory instruments by specifying innodb as the code area.

   mysql> SELECT * FROM performance_schema.setup_instruments
          WHERE NAME LIKE '%memory/innodb%';
   +-------------------------------------------+---------+-------+
   | NAME                                      | ENABLED | TIMED |
   +-------------------------------------------+---------+-------+
   | memory/innodb/adaptive hash index         | 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    |
   ...

   Depending on your MySQL installation, code areas may include performance_schema, sql, client, innodb, myisam, csv, memory, blackhole, archive, partition, and others.

2. To enable memory instruments, add a performance-schema-instrument rule to your MySQL configuration file. For example, to enable all memory instruments, add this rule to your configuration file and restart the server:

   performance-schema-instrument='memory/%=COUNTED'

   Note

   Enabling memory instruments at startup ensures that memory allocations that occur at startup are counted.

   After restarting the server, the ENABLED column of the Performance Schema setup_instruments table should report YES for memory instruments that you enabled. The TIMED column in the setup_instruments table is ignored for memory instruments because memory operations are not timed.

   mysql> SELECT * FROM performance_schema.setup_instruments
          WHERE NAME LIKE '%memory/innodb%';
   +-------------------------------------------+---------+-------+
   | NAME                                      | ENABLED | TIMED |
   +-------------------------------------------+---------+-------+
   | memory/innodb/adaptive hash index         | 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    |
   ...

3. Query memory instrument data. In this example, memory instrument data is queried in the Performance Schema memory_summary_global_by_event_name table, which summarizes data by EVENT_NAME. The EVENT_NAME is the name of the instrument.

   The following query returns memory data for the InnoDB buffer pool. For column descriptions, see Section 25.12.15.9, “Memory Summary Tables”.

   mysql> SELECT * FROM performance_schema.memory_summary_global_by_event_name
          WHERE EVENT_NAME LIKE 'memory/innodb/buf_buf_pool'\G
                     EVENT_NAME: memory/innodb/buf_buf_pool
                    COUNT_ALLOC: 1
                     COUNT_FREE: 0
      SUM_NUMBER_OF_BYTES_ALLOC: 137428992
       SUM_NUMBER_OF_BYTES_FREE: 0
                 LOW_COUNT_USED: 0
             CURRENT_COUNT_USED: 1
                HIGH_COUNT_USED: 1
       LOW_NUMBER_OF_BYTES_USED: 0
   CURRENT_NUMBER_OF_BYTES_USED: 137428992
      HIGH_NUMBER_OF_BYTES_USED: 137428992

   The same underlying data can be queried using the sys schema memory_global_by_current_bytes table, which shows current memory usage within the server globally, broken down by allocation type.

   mysql> SELECT * FROM sys.memory_global_by_current_bytes
          WHERE event_name LIKE 'memory/innodb/buf_buf_pool'\G
   *************************** 1. row ***************************
          event_name: memory/innodb/buf_buf_pool
       current_count: 1
       current_alloc: 131.06 MiB
   current_avg_alloc: 131.06 MiB
          high_count: 1
          high_alloc: 131.06 MiB
      high_avg_alloc: 131.06 MiB

   This sys schema query aggregates currently allocated memory (current_alloc) by code area:

   mysql> SELECT SUBSTRING_INDEX(event_name,'/',2) AS
          code_area, sys.format_bytes(SUM(current_alloc))
          AS current_alloc
          FROM sys.x$memory_global_by_current_bytes
          GROUP BY SUBSTRING_INDEX(event_name,'/',2)
          ORDER BY SUM(current_alloc) DESC;
   +---------------------------+---------------+
   | code_area                 | current_alloc |
   +---------------------------+---------------+
   | memory/innodb             | 843.24 MiB    |
   | memory/performance_schema | 81.29 MiB     |
   | memory/mysys              | 8.20 MiB      |
   | memory/sql                | 2.47 MiB      |
   | memory/memory             | 174.01 KiB    |
   | memory/myisam             | 46.53 KiB     |
   | memory/blackhole          | 512 bytes     |
   | memory/federated          | 512 bytes     |
   | memory/csv                | 512 bytes     |
   | memory/vio                | 496 bytes     |
   +---------------------------+---------------+

   For more information about sys schema, see Chapter 26, MySQL sys Schema.