MySQL专题 2 数据库优化 Slow Query log

　　MySQL Server 有四种类型的日志——Error Log、General Query Log、Binary Log 和 Slow Query Log。

　　第一个是错误日志，记录 mysqld 的一些错误。第二个是一般查询日志，记录 mysqld 正在做的事情，比如客户端的连接和断开、来自客户端每条 Sql Statement 记录信息；如果你想准确知道客户端到底传了什么瞎 [哔哔] 玩意儿给服务端，这个日志就非常管用了，不过它非常影响性能。第四个是慢查询日志，记录一些查询比较慢的 SQL 语句——这种日志非常常用，主要是给开发者调优用的。

　　剩下的第三种就是 Binlog 了，包含了一些事件，这些事件描述了数据库的改动，如建表、数据改动等，也包括一些潜在改动，比如

DELETE FROM ran WHERE bing = luan

，然而一条数据都没被删掉的这种情况。除非使用 Row-based logging，否则会包含所有改动数据的 SQL Statement。

　　那么 Binlog 就有了两个重要的用途——复制和恢复。比如主从表的复制，和备份恢复什么的。

Mysql slow query log

一、概念部分：

顾名思义，慢查询日志中记录的是执行时间较长的query，也就是我们常说的slow query，通过设--log-slow-queries[=file_name]来打开该功能并设置记录位置和文件名，默认文件名为hostname-slow.log，默认目录也是数据目录。
慢查询日志采用的是简单的文本格式，可以通过各种文本编辑器查看其中的内容。其中记录了语句执行的时刻，执行所消耗的时间，执行用户，连接主机等相关信息。MySQL还提供了专门用来分析满查询日志的工具程序mysqlslowdump，用来帮助数据库管理人员解决可能存在的性能问题。

二、slow query log相关变量

2.1、命令行参数：

--log-slow-queries

指定日志文件存放位置，可以为空，系统会给一个缺省的文件host_name-slow.log

2.2、系统变量

log_slow_queries

指定日志文件存放位置，可以为空，系统会给一个缺省的文件host_name-slow.log

slow_query_log

slow quere log的开关，当值为1的时候说明开启慢查询。

slow_query_log_file

指定日志文件存放位置，可以为空，系统会给一个缺省的文件host_name-slow.log

long_query_time

记录超过的时间，默认为10s

log_queries_not_using_indexes

log下来没有使用索引的query，可以根据情况决定是否开启

三、实验部分：

----使用log_slow_queries参数打开慢查询，由于该参数已经过时，因此在err日志中将出现提示信息
----修改my.cnf文件，添加log_slow_queries参数
[root@node4 ~]# vi /opt/mysql5.5/my.cnf
[root@node4 ~]# cat /opt/mysql5.5/my.cnf |grep '^log_slow'
log_slow_queries = /tmp/mysqlslow.log
----清空err日志内容：
[root@node4 ~]# cat /dev/null > /tmp/mysql3306.err
[root@node4 ~]# service mysql start
Starting MySQL....                                         [  OK  ]
----查看err日志的信息
[root@node4 data]# tail -f /tmp/mysql3306.err
130801 02:26:28 mysqld_safe Starting mysqld daemon with databases from /opt/mysql5.5/data
130801  2:26:28 [Warning] The syntax '--log-slow-queries' is deprecated and will be removed in a future release. Please use '--slow-query-log'/'--slow-query-log-file' instead.
130801  2:26:28 [Warning] You need to use --log-bin to make --binlog-format work.
130801  2:26:28 InnoDB: The InnoDB memory heap is disabled
130801  2:26:28 InnoDB: Mutexes and rw_locks use InnoDB's own implementation
130801  2:26:28 InnoDB: Compressed tables use zlib 1.2.3
130801  2:26:28 InnoDB: Initializing buffer pool, size = 128.0M
130801  2:26:28 InnoDB: Completed initialization of buffer pool
130801  2:26:28 InnoDB: highest supported file format is Barracuda.
130801  2:26:28  InnoDB: Waiting for the background threads to start
130801  2:26:30 InnoDB: 1.1.8 started; log sequence number 3069452
130801  2:26:30 [Note] Event Scheduler: Loaded 0 events
130801  2:26:30 [Note] /opt/mysql5.5/bin/mysqld: ready for connections.
Version: '5.5.22-log'  socket: '/tmp/mysql.sock'  port: 3306  Source distribution

----使用slow_query_log和slow_query_log_file
[root@node4 ~]# vi /opt/mysql5.5/my.cnf
[root@node4 ~]# cat /opt/mysql5.5/my.cnf |grep '^slow_query'
slow_query_log = 1
slow_query_log_file = /tmp/mysqlslow.log1

[root@node4 ~]# service mysql start
Starting MySQL...                                          [  OK  ]
[root@node4 ~]# mysql
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 1
Server version: 5.5.22-log Source distribution

Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> show variables like '%slow%';
+---------------------+---------------------+
| Variable_name       | Value               |
+---------------------+---------------------+
| log_slow_queries    | ON                  |
| slow_launch_time    | 10                   |
| slow_query_log      | ON                  |
| slow_query_log_file | /tmp/mysqlslow.log1 |
+---------------------+---------------------+
4 rows in set (0.00 sec)

----关于slow_launch_time参数，首先修改一下参数值
mysql> set global long_query_time=1;
Query OK, 0 rows affected (0.00 sec)
mysql> show variables like '%long_query%';
+-----------------+----------+
| Variable_name   | Value    |
+-----------------+----------+
| long_query_time | 1.000000 |
+-----------------+----------+
1 row in set (0.00 sec)

----进行一下相关操作，查看/tmp/mysqlslow.log1的内容
mysql> select database();
+------------+
| database() |
+------------+
| NULL       |
+------------+
1 row in set (0.00 sec)

mysql> use test;
Database changed
mysql> show tables;
Empty set (0.00 sec)

mysql> create table t as select * from information_schema.tables;
Query OK, 85 rows affected (0.38 sec)
Records: 85  Duplicates: 0  Warnings: 0

mysql> insert into t select * from t;
Query OK, 85 rows affected (0.05 sec)
Records: 85  Duplicates: 0  Warnings: 0

mysql> insert into t select * from t;
Query OK, 170 rows affected (0.03 sec)
Records: 170  Duplicates: 0  Warnings: 0

mysql> insert into t select * from t;
Query OK, 340 rows affected (0.05 sec)
Records: 340  Duplicates: 0  Warnings: 0

mysql> insert into t select * from t;
Query OK, 680 rows affected (0.08 sec)
Records: 680  Duplicates: 0  Warnings: 0

mysql> insert into t select * from t;
Query OK, 1360 rows affected (0.29 sec)
Records: 1360  Duplicates: 0  Warnings: 0

mysql> insert into t select * from t;
Query OK, 2720 rows affected (1.49 sec)
Records: 2720  Duplicates: 0  Warnings: 0

----在这里已经超过1s了，查看/tmp/mysqlslow.log1
[root@node4 data]# tail -f /tmp/mysqlslow.log1
# Time: 130801  2:36:25
# User@Host: root[root] @ localhost []
# Query_time: 2.274219  Lock_time: 0.000322 Rows_sent: 0  Rows_examined: 5440
use test;
SET timestamp=1375295785;
insert into t select * from t;

----log_queries_not_using_indexes参数实验
mysql> show variables like '%indexes%';
+-------------------------------+-------+
| Variable_name                 | Value |
+-------------------------------+-------+
| log_queries_not_using_indexes | OFF   |
+-------------------------------+-------+
1 row in set (0.00 sec)

mysql> set log_queries_not_using_indexes = 1;
ERROR 1229 (HY000): Variable 'log_queries_not_using_indexes' is a GLOBAL variable and should be set with SET GLOBAL
mysql> set global log_queries_not_using_indexes = 1;
Query OK, 0 rows affected (0.01 sec)

mysql> show variables like '%indexes%';
+-------------------------------+-------+
| Variable_name                 | Value |
+-------------------------------+-------+
| log_queries_not_using_indexes | ON    |
+-------------------------------+-------+
1 row in set (0.00 sec)

mysql> desc t;
+-----------------+---------------------+------+-----+---------+-------+
| Field           | Type                | Null | Key | Default | Extra |
+-----------------+---------------------+------+-----+---------+-------+
| TABLE_CATALOG   | varchar(512)        | NO   |     |         |       |
| TABLE_SCHEMA    | varchar(64)         | NO   |     |         |       |
| TABLE_NAME      | varchar(64)         | NO   |     |         |       |
| TABLE_TYPE      | varchar(64)         | NO   |     |         |       |
| ENGINE          | varchar(64)         | YES  |     | NULL    |       |
| VERSION         | bigint(21) unsigned | YES  |     | NULL    |       |
| ROW_FORMAT      | varchar(10)         | YES  |     | NULL    |       |
| TABLE_ROWS      | bigint(21) unsigned | YES  |     | NULL    |       |
| AVG_ROW_LENGTH  | bigint(21) unsigned | YES  |     | NULL    |       |
| DATA_LENGTH     | bigint(21) unsigned | YES  |     | NULL    |       |
| MAX_DATA_LENGTH | bigint(21) unsigned | YES  |     | NULL    |       |
| INDEX_LENGTH    | bigint(21) unsigned | YES  |     | NULL    |       |
| DATA_FREE       | bigint(21) unsigned | YES  |     | NULL    |       |
| AUTO_INCREMENT  | bigint(21) unsigned | YES  |     | NULL    |       |
| CREATE_TIME     | datetime            | YES  |     | NULL    |       |
| UPDATE_TIME     | datetime            | YES  |     | NULL    |       |
| CHECK_TIME      | datetime            | YES  |     | NULL    |       |
| TABLE_COLLATION | varchar(32)         | YES  |     | NULL    |       |
| CHECKSUM        | bigint(21) unsigned | YES  |     | NULL    |       |
| CREATE_OPTIONS  | varchar(255)        | YES  |     | NULL    |       |
| TABLE_COMMENT   | varchar(2048)       | NO   |     |         |       |
+-----------------+---------------------+------+-----+---------+-------+
21 rows in set (0.05 sec)
----下面的命令是查看索引的
mysql> show index from t;
Empty set (0.01 sec)

mysql> select * from t where engine='xxx';
Empty set (0.18 sec)

# Time: 130801  2:43:43
# User@Host: root[root] @ localhost []
# Query_time: 0.185773  Lock_time: 0.148868 Rows_sent: 0  Rows_examined: 5440
SET timestamp=1375296223;
select * from t where engine='xxx';

四、Mysqldumpslow

如果日志内容很多，用眼睛一条一条看会累死，mysql自带了分析的工具，使用方法如下：

[root@node4 data]# 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
-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