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MySQL內存使用的查看方式詳解

前言

本文主要給大家介紹了關于MySQL內存使用查看的相關內容，分享出來供大家參考學習，下面話不多說了，來一起看看詳細的介紹吧

使用版本：MySQL 5.7

官方文檔

在performance_schema有如下表記錄內存使用情況

mysql> show tables like '%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  |
+-------------------------------------------------+

每個內存統計表都有如下統計列：

* COUNT_ALLOC，COUNT_FREE：對內存分配和釋放內存函數的調用總次數

* SUM_NUMBER_OF_BYTES_ALLOC，SUM_NUMBER_OF_BYTES_FREE：已分配和已釋放的內存塊的總字節大小

* CURRENT_COUNT_USED：這是一個便捷列，等于COUNT_ALLOC - COUNT_FREE

* CURRENT_NUMBER_OF_BYTES_USED：當前已分配的內存塊但未釋放的統計大小。這是一個便捷列，等于SUM_NUMBER_OF_BYTES_ALLOC - SUM_NUMBER_OF_BYTES_FREE

* LOW_COUNT_USED，HIGH_COUNT_USED：對應CURRENT_COUNT_USED列的低和高水位標記

* LOW_NUMBER_OF_BYTES_USED，HIGH_NUMBER_OF_BYTES_USED：對應CURRENT_NUMBER_OF_BYTES_USED列的低和高水位標記

內存統計表允許使用TRUNCATE TABLE語句。使用truncate語句時有如下行為：

* 通常，truncate操作會重置統計信息的基準數據（即清空之前的數據），但不會修改當前server的內存分配等狀態。也就是說，truncate內存統計表不會釋放已分配內存

* 將COUNT_ALLOC和COUNT_FREE列重置，并重新開始計數（等于內存統計信息以重置后的數值作為基準數據）

* SUM_NUMBER_OF_BYTES_ALLOC和SUM_NUMBER_OF_BYTES_FREE列重置與COUNT_ALLOC和COUNT_FREE列重置類似

* LOW_COUNT_USED和HIGH_COUNT_USED將重置為CURRENT_COUNT_USED列值

* LOW_NUMBER_OF_BYTES_USED和HIGH_NUMBER_OF_BYTES_USED將重置為CURRENT_NUMBER_OF_BYTES_USED列值

* 此外，按照帳戶，主機，用戶或線程分類統計的內存統計表或memory_summary_global_by_event_name表，如果在對其依賴的accounts、hosts、users表執行truncate時，會隱式對這些內存統計表執行truncate語句

簡單來說，就是可以根據用戶、主機、線程、賬號、全局的維度對內存進行監控。同時庫sys也就這些表做了進一步的格式化，可以使得用戶非常容易的觀察到每個對象的內存開銷：

mysql> select event_name,current_alloc from sys.memory_global_by_current_bytes limit 10;
+-----------------------------------------------------------------------------+---------------+
| event_name         | current_alloc |
+-----------------------------------------------------------------------------+---------------+
| memory/performance_schema/events_statements_history_long   | 13.66 MiB |
| memory/performance_schema/events_statements_history_long.sqltext  | 9.77 MiB |
| memory/performance_schema/events_statements_history_long.tokens  | 9.77 MiB |
| memory/performance_schema/events_statements_summary_by_digest.tokens | 9.77 MiB |
| memory/performance_schema/table_handles     | 9.06 MiB |
| memory/performance_schema/events_statements_summary_by_thread_by_event_name | 8.67 MiB |
| memory/sql/String::value       | 6.02 MiB |
| memory/performance_schema/memory_summary_by_thread_by_event_name  | 5.62 MiB |
| memory/performance_schema/events_statements_summary_by_digest  | 4.88 MiB |
| memory/sql/TABLE        | 4.35 MiB |
+-----------------------------------------------------------------------------+---------------+

默認情況下performance_schema只對performance_schema進行了內存開銷的統計。根據你的MySQL安裝代碼區域可能包括performance_schema、sql、client、innodb、myisam、csv、memory、blackhole、archive、partition和其他。

查看innodb相關的內存監控是否開啟，默認不開啟

mysql> SELECT * FROM performance_schema.setup_instruments
 -> WHERE NAME LIKE '%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 |

可以通過條件縮小范圍：

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 |

對所有可能的對象進行內存監控。因此，還需要做下面的設置：

mysql> update performance_schema.setup_instruments set enabled = 'yes' where name like 'memory%';
Query OK, 306 rows affected (0.00 sec)
Rows matched: 376 Changed: 306 Warnings: 0

但是這種在線打開內存統計的方法僅對之后新增的內存對象有效，重啟數據庫后又會還原設置：

如想要對全局生命周期中的對象進行內存統計，必須在配置文件中進行設置，然后重啟：

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

可以使用sys庫下的memory_global_by_current_bytes表來查詢相同的底層數據，該模式表顯示了全局服務器內當前內存使用情況，按分配類型進行細分。

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

此sys模式查詢通過current_alloc()代碼區域聚合當前分配的內存：

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 |
+---------------------------+---------------+

總結

以上就是這篇文章的全部內容了，希望本文的內容對大家的學習或者工作具有一定的參考學習價值，如果有疑問大家可以留言交流，謝謝大家對腳本之家的支持。

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