MySQL日誌管理之通用日誌和慢查詢日誌

MySQL的通用日誌：

用來記錄對資料庫的通用操作，包括錯誤的sql語句等信息。

通用日誌可以保存在：file（預設值）或 table（mysql.general_log表）

mysql通用日誌的設置：

general_log=ON|OFF  --- 是否啟用通用日誌

general_log_file=HOSTNAME.log ---#通用日誌存放的文件路徑

log_output=TABLE|FILE|NONE --- 通用日誌的存放方式

範例：

#查看是否啟用通用日誌：
mysql> select @@general_log;
+---------------+
| @@general_log |
+---------------+
|             0 |
+---------------+
1 row in set (0.00 sec)

mysql> show variables like "general_log";
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| general_log   | OFF   |
+---------------+-------+
1 row in set (0.00 sec)

general_log是一個全局變數。

#查看通用日誌的存放路徑
mysql> select @@general_log_file;
+-------------------------+
| @@general_log_file      |
+-------------------------+
| /data/mysql/CentOS8.log |
+-------------------------+
1 row in set (0.00 sec)

hostname.log

#啟用通用日誌
mysql> set general_log=1;
ERROR 1229 (HY000): Variable 'general_log' is a GLOBAL variable and should be set with SET GLOBAL

mysql> set global  general_log=1;
Query OK, 0 rows affected (0.00 sec)

#通用日誌預設村存放在file中
mysql> show variables like 'log_output';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| log_output    | FILE  |
+---------------+-------+
1 row in set (0.00 sec)

mysql> show global variables like 'log_output';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| log_output    | FILE  |
+---------------+-------+
1 row in set (0.00 sec)

#修改通用日誌的預設存放

將通用日誌存放在一張表中
mysql> set global log_output="table";
Query OK, 0 rows affected (0.00 sec)

mysql> SHOW GLOBAL VARIABLES LIKE 'log_output';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| log_output    | TABLE |
+---------------+-------+
1 row in set (0.00 sec)

#改為存放到表以後，通用日誌是存放在mysql資料庫的gerneral_log這張表中的。
mysql> use mysql;
Database changed
mysql> show tables;
+---------------------------+
| Tables_in_mysql           |
+---------------------------+
| columns_priv              |
| db                        |
| event                     |
| func                      |
| general_log               |
| help_category             |
| help_keyword              |
| help_relation             |
| help_topic                |
| innodb_index_stats        |
| innodb_table_stats        |
| ndb_binlog_index          |
| plugin                    |
| proc                      |
| procs_priv                |
| proxies_priv              |
| servers                   |
| slave_master_info         |
| slave_relay_log_info      |
| slave_worker_info         |
| slow_log                  |
| tables_priv               |
| time_zone                 |
| time_zone_leap_second     |
| time_zone_name            |
| time_zone_transition      |
| time_zone_transition_type |
| user                      |
+---------------------------+
28 rows in set (0.00 sec)

#查看general_log表
mysql> select * from general_log;
+---------------------+---------------------------+-----------+-----------+--------------+---------------------------+
| event_time          | user_host                 | thread_id | server_id | command_type | argument                  |
+---------------------+---------------------------+-----------+-----------+--------------+---------------------------+
| 2022-09-17 12:41:03 | root[root] @ localhost [] |         2 |         0 | Query        | select * from general_log |
+---------------------+---------------------------+-----------+-----------+--------------+---------------------------+
1 row in set (0.00 sec)

mysql> show table status like 'general_log'\G

general_log這張表就是一個CSV（文本文件）中，
文件路徑：mysql數據文件存放位置（預設/var/lib/mysql）裡面的mysql目錄中。

[root@CentOS8 mysql]# pwd
/data/mysql/mysql
[root@CentOS8 mysql]# cat general_log.CSV
"2022-09-17 12:41:03","root[root] @ localhost []",2,0,"Query","select * from general_log"
"2022-09-17 12:41:52","root[root] @ localhost []",2,0,"Query","show table status like 'general_log'"
"2022-09-17 12:41:56","root[root] @ localhost []",2,0,"Query","show table status like 'general_log'"
"2022-09-17 12:43:27","root[root] @ localhost []",2,0,"Query","select * from general_log"
"2022-09-17 12:45:57","root[root] @ localhost []",2,0,"Query","show table status like 'general_log'"

通用日誌的作用：用來觀察資料庫發生的事件。

MySQL的慢查詢日誌

記錄執行查詢時長超出指定時長的操作

慢查詢日誌的相關設置；

#預設沒有啟用慢查詢日誌
slow_query_log=ON|OFF #開啟或關閉慢查詢，支持全局和會話，只有全局設置才會生成慢查詢文件

long_query_time=N #慢查詢的閥值，單位秒,預設為10s，超過這個時間就叫慢查詢

slow_query_log_file=HOSTNAME-slow.log  #記錄慢查詢日誌的文件

log_slow_filter = admin,filesort,filesort_on_disk,
		  full_join,full_scan,
		  query_cache,query_cache_miss,
		  tmp_table,tmp_table_on_disk
#上述查詢類型且查詢時長超過long_query_time，則記錄日誌 慢查詢記錄的相關行為

log_queries_not_using_indexes=ON  #執行sql語句的時候沒有利用索引或者使用全索引掃描，不管是否超過閾值都要記錄在慢查詢日誌中。（預設OFF，即不記錄）

log_slow_rate_limit = 1 #多少次查詢才記錄，mariadb特有

log_slow_verbosity= Query_plan,explain #記錄內容

log_slow_queries = OFF    #同slow_query_log，MariaDB 10.0/MySQL 5.6.1 版後已刪除

#開啟慢查詢
mysql> set global slow_query_log=1;
Query OK, 0 rows affected (0.00 sec)

mysql> select @@slow_query_log;
+------------------+
| @@slow_query_log |
+------------------+
|                1 |
+------------------+
1 row in set (0.00 sec)

#修改慢查詢的預設值
mysql> set long_query_time=1;
Query OK, 0 rows affected (0.00 sec)

mysql> select @@long_query_time;
+-------------------+
| @@long_query_time |
+-------------------+
|          1.000000 |
+-------------------+
1 row in set (0.00 sec)

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