MySQL-负载很高排查思路

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本文介绍了一套用于诊断MySQL高负载问题的方法，包括使用htop、dstat等工具监控CPU及IO负载，通过tcpdump捕获SQL查询并分析，利用strace检查系统调用异常，以及调整MySQL配置参数。

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思路：
1、确定高负载的类型 htop，dstat命令看负载高是CPU还是IO
2、监控具体的sql语句，是insert update 还是 delete导致高负载
3、检查mysql日志
4、检查硬件问题

dstat

可以看到具体是哪个用户哪个进程占用了相关系统资源，当前CPU、内存谁在使用

htop

htop是top的增强版，更直观

tcpdump

抓取mysql包分析，一般抓3306端口的数据

[root@cc ~]# tcpdump -i eth0 -A -s 3000 port 3306 > ~/sql.log

然后使用awk,sort,wc 等命令进行分析

或者

[root@cc ~]# tcpdump -i eth0 -s 0 -l -w - dst port 3306 | strings | perl -e '
while(<>) { chomp; next if /^[^ ]+[ ]*$/;
if(/^(SELECT|UPDATE|DELETE|INSERT|SET|COMMIT|ROLLBACK|CREATE|DROP|ALTER)/i) {
    if (defined $q) { print "$qn"; }
    $q=$_;
    } else {
    $_ =~ s/^[ t]+//; $q.=" $_";
    }
}'

就可以看出最繁忙的sql语句了

strace

查看系统调用是否有问题，进程是否堵塞，是否有Broken pipe

[root@cc ~]# strace -p 26578

pt-query-digest

分析mysql慢日志，查看哪些sql语句最耗时

[root@cc ~]#  pt-query-digest slow.logs

# 390ms USER TIME, 10ms system TIME, 15.67M rss, 105.84M vsz  
# CURRENT DATE: Thu DEC 29 13:22:42 2014  
# Hostname: test   
# Files: slow.log  
# Overall: 776 total, 11 UNIQUE, 0.00 QPS, 0.00x concurrency _____________  
# TIME range: 2011-09-10 04:03:19 TO 2011-12-29 05:02:51  
# Attribute          total     MIN     MAX     avg     95%  stddev  median  
# ============     ======= ======= ======= ======= ======= ======= =======  
# EXEC TIME          5657s      2s     33s      7s     23s      6s      5s  
# LOCK TIME            33s       0     19s    43ms    98us   715ms    38us  
# ROWS sent        323.38k       0 107.36k  426.73    0.99   6.35k       0  
# ROWS examine     323.39k       0 107.36k  426.74       0   6.35k       0  
# Query SIZE       217.95k      38     562  287.61  420.77   81.78  284.79

show processlist

查看系统到底在干什么


mysql> show full processlist;
+-----------+---------------+---------------------+---------------------+---------+------+---------------+---------------------------+
| Id        | User          | Host                | db                  | Command | Time | State         | Info                      |
+-----------+---------------+---------------------+---------------------+---------+------+---------------+---------------------------+
| 184498848 | testdb_rr1356 | 10.11.211.120:61343 | testdb_rr1356_db121 | Sleep   | 1384 |               | NULL                      |
| 184508740 | testdb_rr1356 | 10.11.211.120:11809 | testdb_rr1356_db121 | Sleep   |   87 |               | NULL                      |
| 184509415 | testdb_rr1356 | 10.11.211.120:12760 | testdb_rr1356_db121 | Query   |    0 | NULL          | show full processlist     |
| 184509451 | testdb_rr1356 | 10.11.211.120:12804 | testdb_rr1356_db121 | Sleep   |   10 |               | NULL                      |
| 184509528 | testdb_rr1356 | 10.11.211.120:12919 | testdb_rr1356_db121 | Query   |    0 | freeing items | DESCRIBE test_channel     |

检查mysql配置参数是否有问题，引起大量的IO或者高CPU操作

innodb_flush_log_at_trx_commit 、innodb_buffer_pool_size 、key_buffer_size 等重要参数

mysql> show variables like '%innodb%';
+---------------------------------+----------------------------+
| Variable_name                   | Value                      |
+---------------------------------+----------------------------+
| have_innodb                     | YES                        |
| ignore_builtin_innodb           | ON                         |
| innodb_adaptive_flushing        | ON                         |
| innodb_adaptive_hash_index      | ON                         |
| innodb_additional_mem_pool_size | 2097152                    |
| innodb_autoextend_increment     | 8                          |
| innodb_autoinc_lock_mode        | 1                          |
| innodb_buffer_pool_size         | 2013265920                 |
| innodb_change_buffering         | inserts                    |
| innodb_checksums                | ON                         |

通过show engine innodb status查看当前事务，内存使用

mysql> show engine innodb status  \G

LATEST DETECTED DEADLOCK
------------------------
150731 10:36:50
*** (1) TRANSACTION:
TRANSACTION EBFBBEC, ACTIVE 0 sec, process no 20691, OS thread id 47345217033984 inserting
mysql tables in use 1, locked 1
LOCK WAIT 5 lock struct(s), heap size 1248, 4 row lock(s), undo log entries 2
MySQL thread id 143249904, query id 1286731854 10.135.21.120 tybuser2014 update

#此处具体sql省略

----------------------
BUFFER POOL AND MEMORY
----------------------
Total memory allocated 2058485760; in additional pool allocated 0
Dictionary memory allocated 819282
Buffer pool size   122879
Free buffers       97599
Database pages     24313
Old database pages 8954
Modified db pages  7
Pending reads 0
Pending writes: LRU 0, flush list 0, single page 0
Pages made young 6, not young 0
0.00 youngs/s, 0.00 non-youngs/s
Pages read 1049, created 41853, written 30401604
0.00 reads/s, 0.00 creates/s, 1.75 writes/s
Buffer pool hit rate 1000 / 1000, young-making rate 0 / 1000 not 0 / 1000
Pages read ahead 0.00/s, evicted without access 0.00/s, Random read ahead 0.00/s
LRU len: 24313, unzip_LRU len: 0
I/O sum[45]:cur[0], unzip sum[0]:cur[0]

最后通过zabbix或者cacti等监控来查看IO、CPU、MEMORY、磁盘等是否有异常

这样基本上就可以把问题找出来了

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