1. MySQL 慢查询定位
1.1 MySQL 慢查询日志格式
--MySQL 慢查询日志格式
1）Time 日志的记录时间
2) User@Host 执行SQL的用户和主机
3) Query_time SQL执行的耗时时间
4) Lock_time 锁表的时间
5) Rows_sent SQL返回的执行记录条数
6) Rows_examined SQL语句扫描的记录条数
7) SET timestamp SQL语句执行的时间点
8) select SQL执行语句
1.2 MySQL 慢查询日志配置
slow_query_log
slow_query_log_file
long_query_time
log_queries_not_using_indexes
-- 显示慢查询的配置变量
mysql> show global variables like '%slow%';
+---------------------------+-------------------------------+
| Variable_name | Value |
+---------------------------+-------------------------------+
| log_slow_admin_statements | OFF |
| log_slow_slave_statements | OFF |
| slow_launch_time | 2 |
| slow_query_log | OFF |
| slow_query_log_file | /data/mysql/data/11g-slow.log |
+---------------------------+-------------------------------+
5 rows in set (0.11 sec)
1.3 打开慢查询日志开关 ON/OFF
set global slow_query_log = on;
set global slow_query_log = off;1) 慢查询日志文件的路径和文件名
mysql> show global variables like 'slow_query_log_file';
+---------------------+-------------------------------+
| Variable_name | Value |
+---------------------+-------------------------------+
| slow_query_log_file | /data/mysql/data/11g-slow.log |
+---------------------+-------------------------------+2) 慢查询SQL执行阈值 SQL执行时间超过0.2S算慢查询、会被记录慢查询日志
-- long_query_time 0.2
set global long_query_time = 0.2;
set global long_query_time = 1; --1秒
set global long_query_time = 2; --2秒3) 记录没有使用索引的SQLlog_queries_not_using_indexes ON|OFFmysql> show global variables like 'log_queries_not_using_indexes';
+-------------------------------+-------+
| Variable_name | Value |
+-------------------------------+-------+
| log_queries_not_using_indexes | OFF |
+-------------------------------+-------+
mysql> set global log_queries_not_using_indexes=on;
2. MySQL 慢查询日志工具mysqldumpslow
mysqldumpslow原理: 解析慢查询日志文件.使用Perl脚本语言写的。
MySQL 慢查询日志工具：
mysqldumpslow
mysqlsla
pt-query-digest
[root@11g ~]# 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 defaultal: average lock timear: average rows sentat: average query timec: countl: lock timer: rows sentt: 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-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：
[root@11g data]# mysqldumpslow -s at -t 5 11g-slow.log Reading mysql slow query log from 11g-slow.log
Count: 1 Time=0.00s (0s) Lock=0.00s (0s) Rows=0.0 (0), 0users@0hosts# Time: N-N-07T02:N:N.408513Z# User@Host: root[root] @ localhost [] Id: N# Query_time: N.N Lock_time: N.N Rows_sent: N Rows_examined: NSET timestamp=N;select sleep(N)
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