MySql开启慢查询日志并使用pt-query-digest 分析

慢查询日志会将查询过程中超出你设置的时间的查询记录下来，以便供开发者进行分析和优化。

 

1. 开启慢查询

1.1 查看当前设置

mysql> show variables like "%query%";

输出

+------------------------------+-----------------------------------------+
| variable_name                | value                                   |
+------------------------------+-----------------------------------------+
| binlog_rows_query_log_events | off                                     |
| ft_query_expansion_limit     | 20                                      |
| have_query_cache             | yes                                     |
| long_query_time              | 10.000000                               |
| query_alloc_block_size       | 8192                                    |
| query_cache_limit            | 1048576                                 |
| query_cache_min_res_unit     | 4096                                    |
| query_cache_size             | 16777216                                |
| query_cache_type             | off                                     |
| query_cache_wlock_invalidate | off                                     |
| query_prealloc_size          | 8192                                    |
| slow_query_log               | off                                     |
| slow_query_log_file          | /var/lib/mysql/lgj-lenovo-g470-slow.log |
+------------------------------+-----------------------------------------+

三个参数

• slow_query_log   on/off ,使能开关
• slow_query_log_file   慢查询日志目录和文件名称
• long_query_time    超过该时间则进行记录，5.1之前只设置到秒，5.1开始支持毫秒。

注意，开启慢查询会影响性能，因此应当在某一段时间内开启，记录一段时间后关闭掉。

1.2 配置

lgj@lgj-lenovo-g470:~/db-analysis$ whereis mysql
mysql: /usr/bin/mysql /usr/lib/mysql /etc/mysql /usr/local/mysql /usr/share/mysql /usr/share/man/man1/mysql.1.gz

我的配置文件在/etc/mysql目录下的my.cnf

配置

[mysqld]
port=3307
skip-grant-tables
!includedir /etc/mysql/conf.d/
!includedir /etc/mysql/mysql.conf.d/

#打开慢查询
slow_query_log = on
#设置超时时间为0，也就是记录所有的查询
long_query_time = 0

设置完后保存，重新启动mysql

service mysql  restart

重新查看参数，已经更改。

mysql> show variables like "%query%";
+------------------------------+-----------------------------------------+
| variable_name                | value                                   |
+------------------------------+-----------------------------------------+
| binlog_rows_query_log_events | off                                     |
| ft_query_expansion_limit     | 20                                      |
| have_query_cache             | yes                                     |
| long_query_time              | 0.000000                                |
| query_alloc_block_size       | 8192                                    |
| query_cache_limit            | 1048576                                 |
| query_cache_min_res_unit     | 4096                                    |
| query_cache_size             | 16777216                                |
| query_cache_type             | off                                     |
| query_cache_wlock_invalidate | off                                     |
| query_prealloc_size          | 8192                                    |
| slow_query_log               | on                                      |
| slow_query_log_file          | /var/lib/mysql/lgj-lenovo-g470-slow.log |
+------------------------------+-----------------------------------------+

1.3 查询

 随便执行一条查询语句，然后查看慢查询日志。

/usr/sbin/mysqld, version: 5.7.25-0ubuntu0.18.04.2 ((ubuntu)). started with:
tcp port: 3306  unix socket: /var/run/mysqld/mysqld.sock
time                 id command    argument
/usr/sbin/mysqld, version: 5.7.25-0ubuntu0.18.04.2-log ((ubuntu)). started with:
tcp port: 3306  unix socket: /var/run/mysqld/mysqld.sock
time                 id command    argument
/usr/sbin/mysqld, version: 5.7.25-0ubuntu0.18.04.2-log ((ubuntu)). started with:
tcp port: 3306  unix socket: /var/run/mysqld/mysqld.sock
time                 id command    argument
;
# time: 2019-02-27t14:07:42.841770z
# user@host: skip-grants user[lgj] @ localhost []  id:     2
# query_time: 0.016232  lock_time: 0.000000 rows_sent: 0  rows_examined: 0
set timestamp=1551276462;
;
# time: 2019-02-27t14:07:51.774192z
# user@host: skip-grants user[lgj] @ localhost []  id:     2
# query_time: 0.000485  lock_time: 0.000221 rows_sent: 1  rows_examined: 1
set timestamp=1551276471;
select * from user;
# time: 2019-02-27t14:07:55.839223z
# user@host: skip-grants user[lgj] @ localhost []  id:     2
# query_time: 0.000564  lock_time: 0.000259 rows_sent: 1  rows_examined: 1
set timestamp=1551276475;
# 查询语句
select * from user;
# 记录时间
# time: 2019-02-27t14:08:07.404666z
# user@host: skip-grants user[lgj] @ localhost []  id:     2
#查询时间   锁表时间  
# query_time: 0.006318  lock_time: 0.000435 rows_sent: 13  rows_examined: 1026
set timestamp=1551276487;

从上面可以获知查询时间和锁表时间，但是如果文件比较大，查找时间最长的查询将会非常麻烦，需要使用相关的工具来进行分析。

《高性能mysql》推荐使用 qt-query-digest 工具

2. qt-query-digest的使用

2.1 安装

•   创建目录： mkdir db-analysis && cd db-analysis
•  下载 pt-query-digest: curl -lo https://percona.com/get/pt-query-digest
•   设置执行权限：chmod +x pt-query-digest
•   将慢查询日志的文件复制到当前的目录下
•   执行分析：  ./pt-query-digest lgj-lenovo-g470-slow.log

结果

# 220ms user time, 10ms system time, 33.67m rss, 90.27m vsz
# current date: wed feb 27 22:55:05 2019
# hostname: lgj-lenovo-g470
# files: lgj-lenovo-g470-slow.log
# overall: 9 total, 7 unique, 0.24 qps, 0.00x concurrency ________________
# time range: 2019-02-27t14:07:29 to 2019-02-27t14:08:07
# attribute          total     min     max     avg     95%  stddev  median
# ============     ======= ======= ======= ======= ======= ======= =======
# exec time          185ms   225us   122ms    21ms   122ms    37ms     6ms
# lock time            2ms       0   485us   186us   467us   166us   159us
# rows sent             50       0      13    5.56   12.54    5.25    0.99
# rows examine       2.03k       0   1.00k  230.44 1012.63  419.72    0.99
# query size           198      11      32      22   31.70    7.35   17.65

# profile
# rank query id                          response time calls r/call v/m   
# ==== ================================= ============= ===== ====== ===== 
#    1 0x751417d45b8e80ee5cba2034458b...  0.1223 66.1%     1 0.1223  0.00 show databases
#    2 0xa11944c87a6a5c16fb38455bf703...  0.0320 17.3%     1 0.0320  0.00 select
#    3 0x898255b1be4f8c3044ae35a18286...  0.0155  8.4%     1 0.0155  0.00 admin init db
#    4 0xe77769c62ef669aa7dd5f6760f2d...  0.0134  7.3%     2 0.0067  0.00 show variables
# misc 0xmisc                             0.0018  1.0%     4 0.0004   0.0 <3 items>

# query 1: 0 qps, 0x concurrency, id 0x751417d45b8e80ee5cba2034458b5bc9 at byte 1471
# this item is included in the report because it matches --limit.
# scores: v/m = 0.00
# time range: all events occurred at 2019-02-27t14:07:42
# attribute    pct   total     min     max     avg     95%  stddev  median
# ============ === ======= ======= ======= ======= ======= ======= =======
# count         11       1
# exec time     66   122ms   122ms   122ms   122ms   122ms       0   122ms
# lock time      6   110us   110us   110us   110us   110us       0   110us
# rows sent     20      10      10      10      10      10       0      10
# rows examine   0      10      10      10      10      10       0      10
# query size     7      14      14      14      14      14       0      14
# string:
# databases    microblog
# hosts        localhost
# users        skip-grants user
# query_time distribution
#   1us
#  10us
# 100us
#   1ms
#  10ms
# 100ms  ################################################################
#    1s
#  10s+
show databases\g

# query 2: 0 qps, 0x concurrency, id 0xa11944c87a6a5c16fb38455bf7035609 at byte 1008
# this item is included in the report because it matches --limit.
# scores: v/m = 0.00
# time range: all events occurred at 2019-02-27t14:07:42
# attribute    pct   total     min     max     avg     95%  stddev  median
# ============ === ======= ======= ======= ======= ======= ======= =======
# count         11       1
# exec time     17    32ms    32ms    32ms    32ms    32ms       0    32ms
# lock time      0       0       0       0       0       0       0       0
# rows sent      2       1       1       1       1       1       0       1
# rows examine   0       0       0       0       0       0       0       0
# query size     8      17      17      17      17      17       0      17
# string:
# hosts        localhost
# users        skip-grants user
# query_time distribution
#   1us
#  10us
# 100us
#   1ms
#  10ms  ################################################################
# 100ms
#    1s
#  10s+
# explain /*!50100 partitions*/
select database()\g

# query 3: 0 qps, 0x concurrency, id 0x898255b1be4f8c3044ae35a182869033 at byte 1225
# this item is included in the report because it matches --limit.
# scores: v/m = 0.00
# time range: all events occurred at 2019-02-27t14:07:42
# attribute    pct   total     min     max     avg     95%  stddev  median
# ============ === ======= ======= ======= ======= ======= ======= =======
# count         11       1
# exec time      8    15ms    15ms    15ms    15ms    15ms       0    15ms
# lock time      0       0       0       0       0       0       0       0
# rows sent      0       0       0       0       0       0       0       0
# rows examine   0       0       0       0       0       0       0       0
# query size    15      30      30      30      30      30       0      30
# string:
# databases    microblog
# hosts        localhost
# users        skip-grants user
# query_time distribution
#   1us
#  10us
# 100us
#   1ms
#  10ms  ################################################################
# 100ms
#    1s
#  10s+
administrator command: init db\g

# query 4: 0.05 qps, 0.00x concurrency, id 0xe77769c62ef669aa7dd5f6760f2d2ebb at byte 775
# this item is included in the report because it matches --limit.
# scores: v/m = 0.00
# time range: 2019-02-27t14:07:30 to 2019-02-27t14:08:07
# attribute    pct   total     min     max     avg     95%  stddev  median
# ============ === ======= ======= ======= ======= ======= ======= =======
# count         22       2
# exec time      7    13ms     6ms     7ms     7ms     7ms   559us     7ms
# lock time     54   920us   435us   485us   460us   485us    35us   460us
# rows sent     52      26      13      13      13      13       0      13
# rows examine  98   2.00k   1.00k   1.00k   1.00k   1.00k       0   1.00k
# query size    29      58      29      29      29      29       0      29
# string:
# databases    microblog
# hosts        localhost
# users        skip-grants user
# query_time distribution
#   1us
#  10us
# 100us
#   1ms  ################################################################
#  10ms
# 100ms
#    1s
#  10s+
show variables like "%query%"\g