MySQL慢查詢整理

查看慢查詢是不是開啟{默許是關閉的}
mysql> show variables like "%slow%"; 
+---------------------+----------------------------------+
| Variable_name       | Value                            |
+---------------------+----------------------------------+
| log_slow_queries    | OFF                              |
| slow_launch_time    | 2                                |
| slow_query_log      | OFF                              |
| slow_query_log_file | /mnt/mydata/tkudb-slow.log |
+---------------------+----------------------------------+
4 rows in set (0.00 sec)
開啟慢查詢
mysql> set global slow_query_log='ON';  
Query OK, 0 rows affected (0.01 sec)
驗證慢查詢
mysql> show variables like "%slow%";
+---------------------+----------------------------------+
| Variable_name       | Value                            |
+---------------------+----------------------------------+
| log_slow_queries    | ON                               |
| slow_launch_time    | 2                                |
| slow_query_log      | ON                               |
| slow_query_log_file | /mnt/mydata/tkudb-slow.log |
+---------------------+----------------------------------+
4 rows in set (0.00 sec)

#cat my.cnf
long_query_time = 3
log-slow-queries = /mnt/mydata/tkudb-slow.log 
重啟mysql服務后，設置生效；

系統默許值查看{默許慢查詢的時間為10s}
mysql> show variables like "%long%"; 
+---------------------------------------------------+-----------+
| Variable_name                                     | Value     |
+---------------------------------------------------+-----------+
| long_query_time                                   | 10.000000 |
| max_long_data_size                                | 1048576   |
| performance_schema_events_waits_history_long_size | 10000     |
+---------------------------------------------------+-----------+
3 rows in set (0.00 sec)
mysql> set global long_query_time=3;        
Query OK, 0 rows affected (0.00 sec)

1.利用文本處理工具如notepad+,處理tkudb-slow.log 
2.使用mysqldumpslow工具
[root@tkudb mydata]# mysqldumpslow --help
Usage: mysqldumpslow [ OPTS... ] [ LOGS... ]
Parse and summarize the MySQL slow query log. Options are
  --verbose    verbose
  --debug      debug
  --help       write this text to standard output
  -v           verbose
  -d           debug
  -s ORDER     what to sort by (al, at, ar, c, l, r, t), 'at' is default
                al: average lock time
                ar: average rows sent
                at: average query time
                 c: count
                 l: lock time
                 r: rows sent
                 t: query time  
  -r           reverse the sort order (largest last instead of first)
  -t NUM       just show the top n queries
  -a           don't abstract all numbers to N and strings to 'S'
  -n NUM       abstract numbers with at least n digits within names
  -g PATTERN   grep: only consider stmts that include this string #匹配模式
  -h HOSTNAME  hostname of db server for *-slow.log filename (can be wildcard),
               default is '*', i.e. match all
  -i NAME      name of server instance (if using mysql.server startup script)
  -l           don't subtract lock time from total time
例子：
查詢最后10次log
[root@tkudb mydata]# mysqldumpslow -s r -t 10 /mnt/mydata/tkudb-slow.log
查詢帶有select關鍵詞的最后10次log
[root@tkudb mydata]# mysqldumpslow -s r -t 10 -g 'select' /mnt/mydata/tkudb-slow.log
方法3：集群數據庫，所有主機的慢日志集中寫到某1個監控數據庫的表，由php統1調用顯示！

4.如何定期安全清算slow.log

1.先履行備份，然后對備份文件緊縮打包，最后清除slow.log

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