MySQL的通用日志：
用來記錄對資料庫的通用操作，包括錯誤的sql陳述句等資訊，
通用日志可以保存在：file（默認值）或 table（mysql.general_log表）
mysql通用日志的設定：
general_log=ON|OFF --- 是否啟用通用日志
general_log_file=HOSTNAME.log ---#通用日志存放的檔案路徑
log_output=TABLE|FILE|NONE --- 通用日志的存放方式
范例：
#查看是否啟用通用日志：
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是一個全域變數，
#查看通用日志的存放路徑
mysql> select @@general_log_file;
+-------------------------+
| @@general_log_file |
+-------------------------+
| /data/mysql/CentOS8.log |
+-------------------------+
1 row in set (0.00 sec)
hostname.log
#啟用通用日志
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)
#通用日志默認村存放在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)
#修改通用日志的默認存放
將通用日志存放在一張表中
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)
#改為存放到表以后，通用日志是存放在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（文本檔案）中，
檔案路徑：mysql資料檔案存放位置（默認/var/lib/mysql）里面的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'"
通用日志的作用：用來觀察資料庫發生的事件，
MySQL的慢查詢日志
記錄執行查詢時長超出指定時長的操作
慢查詢日志的相關設定；
#默認沒有啟用慢查詢日志
slow_query_log=ON|OFF #開啟或關閉慢查詢，支持全域和會話，只有全域設定才會生成慢查詢檔案
long_query_time=N #慢查詢的閥值，單位秒,默認為10s，超過這個時間就叫慢查詢
slow_query_log_file=HOSTNAME-slow.log #記錄慢查詢日志的檔案
log_slow_filter = admin,filesort,filesort_on_disk,
full_join,full_scan,
query_cache,query_cache_miss,
tmp_table,tmp_table_on_disk
#上述查詢型別且查詢時長超過long_query_time，則記錄日志 慢查詢記錄的相關行為
log_queries_not_using_indexes=ON #執行sql陳述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志中，（默認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 版后已洗掉
#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)
#修改慢查詢的默認值
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)
慢查詢分析工具mysqldumpslow
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