mysql:慢查询日志slow_query_log

1、慢查询日志：当查询超过一定的时间没有返回结果的时候，才会记录到慢查询日志中。默认不开启。采样的时候手工开启。可以帮助DBA找出执行慢的SQL语句

2、常用的参数详解：

注意：修改以下参数，需要重新启动数据库服务才会生效。
slow_query_log=off|on     --是否开启慢查询日志
slow_query_log_file=filename --指定保存路径及文件名，默认为数据文件目录，hostname-slow.log
long_query_time=    --指定多少秒返回查询的结果为慢查询
long-queries-not-using-indexes　　 --记录所有没有使用到索引的查询语句
min_examined_row_limit=1000　　　　--记录那些由于查找了多余1000次而引发的慢查询
long-slow-admin-statements　　　　 --记录那些慢的optimize table，analyze table和alter table语句
log-slow-Slave-statements　　　　  --记录由Slave所产生的慢查询

3、不重启修改慢查询配置：

set @@global.slow_query_log=
set @@global.slow_query_time=
其他参数可通过以下命令查阅：
show variables  '%slow%';

mysql> show variables like '%slow%';
+---------------------------+-----------------------------------+
| Variable_name             | Value                             |
+---------------------------+-----------------------------------+
| log_slow_admin_statements | OFF                               |
| log_slow_slave_statements | OFF                               |
| slow_launch_time          |                                  |
| slow_query_log            | OFF                               |
| slow_query_log_file       | /var/lib/mysql/localhost-slow.log |
+---------------------------+-----------------------------------+
mysql> show variables like '%long%';
+--------------------------------------------------------+-----------+
| Variable_name                                          | Value     |
+--------------------------------------------------------+-----------+
| long_query_time                                        | 10.000000 |
| performance_schema_events_stages_history_long_size     |      |
| performance_schema_events_statements_history_long_size |      |
| performance_schema_events_waits_history_long_size      |      |
+--------------------------------------------------------+-----------+
 rows in set (0.03 sec)

mysql> show variables like '%min%';
+---------------------------+-------+
| Variable_name             | Value |
+---------------------------+-------+
| ft_min_word_len           |      |
| innodb_ft_min_token_size  |      |
| log_slow_admin_statements | OFF   |
| min_examined_row_limit    |      |
| query_cache_min_res_unit  |   |
+---------------------------+-------+
 rows in set (0.00 sec)

EG:开启慢查询日志：示例

mysql> set global slow_query_log=;
Query OK,  rows affected (0.08 sec)
mysql> set global long_query_time=;
Query OK,  rows affected (0.00 s
mysql> set  long_query_time=;
Query OK,  rows affected (0.05 sec)

[root@localhost mysql]# ls
auto.cnf  ib_logfile0  king                       localhost.log       mysql             mysql_bin.  mysql_bin.  mysql_bin.index  performance_schema  utf8
ibdata1   ib_logfile1  localhost.localdomain.pid  localhost-slow.log  mysql_bin.  mysql_bin.  mysql_bin.  mysql.sock       test                world

mysql> select sleep();
+----------+
| sleep() |
+----------+
|         |
+----------+
 row in set (3.00 sec)

mysql> select sleep();
+----------+
| sleep() |
+----------+
|         |
+----------+
 row in set (4.01 sec)

[root@localhost mysql]# tail -f localhost-slow.log
/usr/local/mysql/bin/mysqld, Version: 5.6.-log (MySQL Community Server (GPL)). started with:
Tcp port:   Unix socket: /var/lib/mysql/mysql.sock
Time                 Id Command    Argument
# Time:  ::
# User@Host: root[root] @ localhost []  Id:
# Query_time: 3.000955  Lock_time: 0.000000 Rows_sent:   Rows_examined:
use king;
SET timestamp=;
select sleep();
# Time:  ::
# User@Host: root[root] @ localhost []  Id:
# Query_time: 4.001169  Lock_time: 0.000000 Rows_sent:   Rows_examined:
SET timestamp=;
select sleep();

4、常用慢查询分析工具：

mysqldumpslow（结果简陋不方便阅读分析）

mysqlsla

percona-toolkit中的pt-query-digest

[root@localhost mysql]# mysqldumpslow localhost-slow.log 

Reading mysql slow query log from localhost-slow.log
Count:   Time=.50s (7s)  Lock=.00s (0s)  Rows=1.0 (), root[root]@localhost
  select sleep(N)

[root@localhost log]# chmod +x mysqlsla-2.03
[root@localhost log]# ll
总用量
-rwxr-xr-x.  root root   11月   mysqlsla-2.03
-rw-r--r--.  root root  4月    percona-toolkit-2.2.-.noarch.rpm
[root@localhost log]# ./mysqlsla-2.03 /var/lib/mysql/localhost-slow.log
Auto-detected logs as slow logs
Report for slow logs: /var/lib/mysql/localhost-slow.log
 queries total,  unique
Sorted by 't_sum'
Grand Totals: Time  s, Lock  s, Rows sent , Rows Examined 

______________________________________________________________________  ___
Count         :   (100.00%)
Time          : 7.002124 s total, 3.501062 s avg, 3.000955 s to 4.001169 s max  (100.00%)
Lock Time (s) :  total,  avg,  to  max  (0.00%)
Rows sent     :  avg,  to  max  (100.00%)
Rows examined :  avg,  to  max  (0.00%)
Database      : king
Users         :
    root@localhost  : 100.00% () of query, 100.00% () of all users

Query abstract:
SET timestamp=N; SELECT sleep(N);

Query sample:
SET timestamp=;
select sleep();

[root@localhost log]# rpm -ivh percona-toolkit-2.2.-.noarch.rpm --nodeps
Preparing...                ########################################### [%]
   :percona-toolkit        ########################################### [%]
[root@localhost log]# pt-query-digest /var/lib/mysql/localhost-slow.log 

# A software update is available:
#   * The current version for Percona::Toolkit is 2.2..

# 820ms user time, 390ms system time, 21.98M rss, 177.44M vsz
# Current date: Mon Mar  ::
# Hostname: localhost.localdomain
# Files: /var/lib/mysql/localhost-slow.log
# Overall:  total,  unique, 0.20 QPS, .70x concurrency ________________
# Time range: -- :: to ::
# Attribute          total     min     max     avg     %  stddev  median
# ============     ======= ======= ======= ======= ======= ======= =======
# Exec time             7s      3s      4s      4s      4s   707ms      4s
# Lock time
# Rows sent
# Rows examine
# Query size                                                 

# Profile
# Rank Query ID           Response time Calls R/Call V/M   Item
# ==== ================== ============= ===== ====== ===== ======
#     0xF9A57DD5A41825CA 7.0021 100.0%      3.5011  0.14 SELECT

# Query : 0.20 QPS, .70x concurrency, ID 0xF9A57DD5A41825CA at byte
# This item is included in the report because it matches --limit.
# Scores: V/M = 0.14
# Time range: -- :: to ::
# Attribute    pct   total     min     max     avg     %  stddev  median
# ============ === ======= ======= ======= ======= ======= ======= =======
# Count
# Exec time          7s      3s      4s      4s      4s   707ms      4s
# Lock time
# Rows sent
# Rows examine
# Query size
# String:
# Databases    king
# Hosts        localhost
# Users        root
# Query_time distribution
#   1us
#  10us
# 100us
#   1ms
#  10ms
# 100ms
#    1s  ################################################################
#  10s+
# EXPLAIN /*!50100 PARTITIONS*/
select sleep()\G