时间：2021-07-01 10:21:17 帮助过：10人阅读
MySQL慢查询日志记录下所有执行超过long_query_time时间的SQL语句，帮你找到执行慢的SQL，方便我们对这些SQL进行优化。
慢查询日志的配置：
默认情况下，mysql没有启用慢查询日志。
[root@rh64 ~]# mysql -u root -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 1
Server version: 5.6.25-73.1 Percona Server (GPL), Release 73.1, Revision 07b797f
Copyright (c) 2009-2015 Percona LLC and/or its affiliates
Copyright (c) 2000, 2015, 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_admin_statements | OFF | | log_slow_filter | | | log_slow_rate_limit | 1 | | log_slow_rate_type | session | | log_slow_slave_statements | OFF | | log_slow_sp_statements | ON | | log_slow_verbosity | | | max_slowlog_files | 0 | | max_slowlog_size | 0 | | slow_launch_time | 2 | | slow_query_log | OFF | | slow_query_log_always_write_time | 10.000000 | | slow_query_log_file | /var/lib/mysql/rh64-slow.log | | slow_query_log_timestamp_always | OFF | | slow_query_log_timestamp_precision | second | | slow_query_log_use_global_control | | +------------------------------------+------------------------------+ 16 rows in set (0.01 sec)
1、可以配置my.cnf文件，服务启动时自动配置
[root@rh64 ~]# cat /etc/my.cnf
[mysqld]
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
user=mysql
# Disabling symbolic-links is recommended to prevent assorted security risks
symbolic-links=0
innodb_data_file_path=ibdata1:12M;ibdata2:10M:autoextend
sql_mode=STRICT_TRANS_TABLES ,NO_ENGINE_SUBSTITUTION
slow_query_log=true
slow_query_log_file = "/var/lib/mysql/rh64-slow.log"
long_query_time=1
log-queries-not-using-indexes=true
[mysqld_safe]
log-error=/var/log/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid
explicit_defaults_for_timestamp=true
innodb_buffer_pool_size = 128M
join_buffer_size = 128M
sort_buffer_size = 2M
read_rnd_buffer_size = 2M
重启server后，查看：
mysql> show variables like '%slow%';
+------------------------------------+------------------------------+ | Variable_name | Value | +------------------------------------+------------------------------+ | log_slow_admin_statements | OFF | | log_slow_filter | | | log_slow_rate_limit | 1 | | log_slow_rate_type | session | | log_slow_slave_statements | OFF | | log_slow_sp_statements | ON | | log_slow_verbosity | | | max_slowlog_files | 0 | | max_slowlog_size | 0 | | slow_launch_time | 2 | | slow_query_log | ON | | slow_query_log_always_write_time | 10.000000 | | slow_query_log_file | /var/lib/mysql/rh64-slow.log | | slow_query_log_timestamp_always | OFF | | slow_query_log_timestamp_precision | second | | slow_query_log_use_global_control | | +------------------------------------+------------------------------+ 16 rows in set (0.00 sec)
2、在系统中配置slow-query-log
mysql> set @@global.slow_query_log = on;
mysql> show variables like '%slow%';
+------------------------------------+------------------------------+ | Variable_name | Value | +------------------------------------+------------------------------+ | log_slow_admin_statements | OFF | | log_slow_filter | | | log_slow_rate_limit | 1 | | log_slow_rate_type | session | | log_slow_slave_statements | OFF | | log_slow_sp_statements | ON | | log_slow_verbosity | | | max_slowlog_files | 0 | | max_slowlog_size | 0 | | slow_launch_time | 2 | | slow_query_log | ON | | slow_query_log_always_write_time | 10.000000 | | slow_query_log_file | /var/lib/mysql/rh64-slow.log | | slow_query_log_timestamp_always | OFF | | slow_query_log_timestamp_precision | second | | slow_query_log_use_global_control | | +------------------------------------+------------------------------+ 16 rows in set (0.00 sec)
3、查看慢查询日志信息
[root@rh64 mysql]# tail rh64-slow.log
use prod; SET timestamp=1449476453; insert into emp1 select * from emp1; # Time: 151207 16:21:11 # User@Host: root[root] @ localhost [] Id: 2 # Schema: prod Last_errno: 0 Killed: 0 # Query_time: 16.748949 Lock_time: 0.000137 Rows_sent: 0 Rows_examined: 1236992 Rows_affected: 618496 # Bytes_sent: 58 SET timestamp=1449476471; insert into emp1 select * from emp1; [root@rh64 mysql]# tail -f rh64-slow.log use prod; SET timestamp=1449476453; insert into emp1 select * from emp1; # Time: 151207 16:21:11 # User@Host: root[root] @ localhost [] Id: 2 # Schema: prod Last_errno: 0 Killed: 0 # Query_time: 16.748949 Lock_time: 0.000137 Rows_sent: 0 Rows_examined: 1236992 Rows_affected: 618496 # Bytes_sent: 58 SET timestamp=1449476471; insert into emp1 select * from emp1; # Time: 151207 16:22:54 # User@Host: root[root] @ localhost [] Id: 2 # Schema: prod Last_errno: 0 Killed: 0 # Query_time: 44.036039 Lock_time: 0.000083 Rows_sent: 0 Rows_examined: 2473984 Rows_affected: 1236992 # Bytes_sent: 59 SET timestamp=1449476574; insert into emp1 select * from emp1; # Time: 151207 16:26:46 # User@Host: root[root] @ localhost [] Id: 2 # Schema: prod Last_errno: 0 Killed: 0 # Query_time: 106.674422 Lock_time: 0.000148 Rows_sent: 0 Rows_examined: 4947968 Rows_affected: 2473984 # Bytes_sent: 59 SET timestamp=1449476806; insert into emp1 select * from emp1;
记录没有使用索引的语句：
mysql> set @@global.log_queries_not_using_indexes=on;
Query OK, 0 rows affected (0.00 sec)
mysql> show variables like '%index%'; +----------------------------------------+-------+ | Variable_name | Value | +----------------------------------------+-------+ | eq_range_index_dive_limit | 10 | | expand_fast_index_creation | OFF | | innodb_adaptive_hash_index | ON | | innodb_adaptive_hash_index_partitions | 1 | | innodb_cmp_per_index_enabled | OFF | | log_bin_index | | | log_queries_not_using_indexes | ON | | log_throttle_queries_not_using_indexes | 0 | | relay_log_index | | +----------------------------------------+-------+ 9 rows in set (0.00 sec)
测试：
mysql> select count(*) from emp1 where empno=7788;
+----------+
| count(*) |
+----------+
| 688128 |
+----------+
1 row in set (4.03 sec)
[root@rh64 mysql]# tail rh64-slow.log
SET timestamp=1449476453; insert into emp1 select * from emp1; # Time: 151207 16:21:11 # User@Host: root[root] @ localhost [] Id: 2 # Schema: prod Last_errno: 0 Killed: 0 # Query_time: 16.748949 Lock_time: 0.000137 Rows_sent: 0 Rows_examined: 1236992 Rows_affected: 618496 # Bytes_sent: 58 SET timestamp=1449476471; insert into emp1 select * from emp1; # Time: 151207 16:22:54 # User@Host: root[root] @ localhost [] Id: 2 # Schema: prod Last_errno: 0 Killed: 0 # Query_time: 44.036039 Lock_time: 0.000083 Rows_sent: 0 Rows_examined: 2473984 Rows_affected: 1236992 # Bytes_sent: 59 SET timestamp=1449476574; insert into emp1 select * from emp1; # Time: 151207 16:26:46 # User@Host: root[root] @ localhost [] Id: 2 # Schema: prod Last_errno: 0 Killed: 0 # Query_time: 106.674422 Lock_time: 0.000148 Rows_sent: 0 Rows_examined: 4947968 Rows_affected: 2473984 # Bytes_sent: 59 SET timestamp=1449476806; insert into emp1 select * from emp1; # Time: 151207 16:30:44 # User@Host: root[root] @ localhost [] Id: 2 # Schema: prod Last_errno: 0 Killed: 0 # Query_time: 4.025612 Lock_time: 0.000098 Rows_sent: 1 Rows_examined: 4947968 Rows_affected: 0 # Bytes_sent: 68 SET timestamp=1449477044; select count(*) from emp1 where empno=7788;
4、通过mysqldumpslow工具查看慢查询日志
[root@rh64 mysql]# mysqldumpslow Can't determine basedir from 'my_print_defaults mysqld' output: --datadir=/var/lib/mysql --socket=/var/lib/mysql/mysql.sock --user=mysql --symbolic-links=0 --innodb_data_file_path=ibdata1:12M;ibdata2:10M:autoextend --sql_mode=STRICT_TRANS_TABLES ,NO_ENGINE_SUBSTITUTION
[root@rh64 mysql]# 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
[root@rh64 mysql]# mysqldumpslow rh64-slow.log
Reading mysql slow query log from rh64-slow.log Count: 3 Time=0.00s (0s) Lock=0.00s (0s) Rows=0.0 (0), root[root]@localhost # Schema: prod Last_errno: N Killed: N # Query_time: N.N Lock_time: N.N Rows_sent: N Rows_examined: N Rows_affected: N # Bytes_sent: N SET timestamp=N; insert into emp1 select * from emp1 Count: 1 Time=0.00s (0s) Lock=0.00s (0s) Rows=0.0 (0), root[root]@localhost # Schema: prod Last_errno: N Killed: N # Query_time: N.N Lock_time: N.N Rows_sent: N Rows_examined: N Rows_affected: N # Bytes_sent: N use prod; SET timestamp=N; insert into emp1 select * from emp1 Count: 1 Time=0.00s (0s) Lock=0.00s (0s) Rows=0.0 (0), root[root]@localhost # Schema: prod Last_errno: N Killed: N # Query_time: N.N Lock_time: N.N Rows_sent: N Rows_examined: N Rows_affected: N # Bytes_sent: N SET timestamp=N; select count(*) from emp1 where empno=N
按照平均锁定时间进行排序，查找前10名：
[root@rh64 mysql]# mysqldumpslow -s al -n 10 rh64-slow.log
Reading mysql slow query log from rh64-slow.log
Count: 3 Time=0.00s (0s) Lock=0.00s (0s) Rows=0.0 (0), root[root]@localhost
# Schema: prod Last_errno: N Killed: N
# Query_time: N.N Lock_time: N.N Rows_sent: N Rows_examined: N Rows_affected: N
# Bytes_sent: N
SET timestamp=N;
insert into emp1 select * from emp1
Count: 1 Time=0.00s (0s) Lock=0.00s (0s) Rows=0.0 (0), root[root]@localhost
# Schema: prod Last_errno: N Killed: N
# Query_time: N.N Lock_time: N.N Rows_sent: N Rows_examined: N Rows_affected: N
# Bytes_sent: N
use prod;
SET timestamp=N;
insert into emp1 select * from emp1
Count: 1 Time=0.00s (0s) Lock=0.00s (0s) Rows=0.0 (0), root[root]@localhost
# Schema: prod Last_errno: N Killed: N
# Query_time: N.N Lock_time: N.N Rows_sent: N Rows_examined: N Rows_affected: N
# Bytes_sent: N
SET timestamp=N;
select count(*) from emp1 where empno=N