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一次诡异的Mysql服务不断重启故障排查

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一次诡异的Mysql服务不断重启故障排查

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前段时间，有测试人员联系我，寻求帮助，让我帮忙看看，测试环境的一台MySQL数据库不断的重启，导致他们的测试无法进行，时间拖的长了，会影响上线进度 。
下面就来说说现象在一个测试环境，mysql5.7部署在centos7.4的系统上，测试人员用LoadRunner进行应用的一个压测测试，压测并发为128，启动LoadRunner过几秒，LoadRunner日志就报错，显示mysql服务断开了，过几秒又恢复，然后又断开，异常诡异 。
排查定位于是就登录到服务器，看一下数据库服务器的内存，内存已经用完了，紧接着就看centos的系统日志（/var/log/messages），在这个日志里发现mysql服务因为OOM，导致进程被系统给kill掉了，然后因为mysql服务有守护进程存在，又被自动启动了 。
一个经验丰富的mysql数据库运维人员，应该很快就知道什么原因导致OOM了 。
第一：mysql数据库的buffer pool内存参数配置不合理
第二：mysql数据库的session初始化内存参数配置不合理
第三：数据库连接总数配置不合理
测试环境的数据库服务器内存为4G，在这里就不谈，为什么测试人员要在这个服务器上做压测，其实做应用压测，应该要用准用的压测环境，而不是随便找个环境就压测，不展开说了 。
模拟复盘测试环境
mysql5.7，centos7.7，内存2G
为了更好的模拟复盘上述故障，这里关闭掉模拟环境的swap，关闭步骤如下所示
[root@localhost data]# free -mtotalusedfreesharedbuff/cacheavailableMem:212456564099171398Swap:204702047[root@localhost data]# swapon -s文件名类型大小已用权限/dev/dm-1partition2097148 264-2[root@localhost data]# swapoff /dev/dm-1[root@localhost data]# free -mtotalusedfreesharedbuff/cacheavailableMem:212425494499251709Swap:000从上面free -m结果中，可以看到swap已经变成0了 。
释放cache占用的内存
[root@localhost data]# sync[root@localhost data]# echo 1 > /proc/sys/vm/drop_caches ;[root@localhost data]# free -mtotalusedfreesharedbuff/cacheavailableMem:212425417849841748Swap:000可以看到目前剩余的内存为1784M，mysql数据库占用内存主要有2大块，第一是：buffer pool占用，第二是：初始化连接占用的内存
在这里设置mysql的buffer pool为1500M，会话的参数设置如下
read_buffer_size = 32Mread_rnd_buffer_size = 32Msort_buffer_size = 32Mtmp_table_size = 32Mmax_heap_table_size=32Mjoin_buffer_size=32M然后5个连接，开始做大查询操作，没过多久，mysql进程就因为OOM被kill了
Aug 31 05:37:40 localhost kernel: Out of memory: Kill process 2534 (mysqld) score 658 or sacrifice childAug 31 05:37:40 localhost kernel: Killed process 2534 (mysqld), UID 1001, total-vm:1825792kB, anon-rss:654388kB, file-rss:0kB, shmem-rss:0kBmysql守护进程就开始启动mysql服务
/u02/mysql/bin/mysqld_safe: 行 198:2534 已杀死nohup /u02/mysql/bin/mysqld --defaults-file=/u02/conf/my3308.cnf --basedir=/u02/mysql --datadir=/u02/data/3308 --plugin-dir=/u02/mysql/lib/plugin --user=mysql --log-error=/u02/log/3308/error.log --open-files-limit=65535 --pid-file=/u02/run/3308/mysqld.pid --socket=/u02/run/3308/mysql.sock --port=3308 < /dev/null > /dev/null 2>&12020-08-30T21:37:40.375749Z mysqld_safe Number of processes running now: 02020-08-30T21:37:40.407781Z mysqld_safe mysqld restarted2020-08-30T21:37:40.666886Z 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details).2020-08-30T21:37:40.667059Z 0 [Note] --secure-file-priv is set to NULL. Operations related to importing and exporting data are disabled2020-08-30T21:37:40.667112Z 0 [Note] /u02/mysql/bin/mysqld (mysqld 5.7.26-log) starting as process 2954 ...2020-08-30T21:37:40.782412Z 0 [Warning] InnoDB: Using innodb_file_format is deprecated and the parameter may be removed in future releases. See http://dev.mysql.com/doc/refman/5.7/en/innodb-file-format.html2020-08-30T21:37:40.782684Z 0 [Note] InnoDB: PUNCH HOLE support available2020-08-30T21:37:40.782729Z 0 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins2020-08-30T21:37:40.782754Z 0 [Note] InnoDB: Uses event mutexes2020-08-30T21:37:40.782772Z 0 [Note] InnoDB: GCC builtin __atomic_thread_fence() is used for memory barrier2020-08-30T21:37:40.782788Z 0 [Note] InnoDB: Compressed tables use zlib 1.2.112020-08-30T21:37:40.782841Z 0 [Note] InnoDB: Adjusting innodb_buffer_pool_instances from 8 to 1 since innodb_buffer_pool_size is less than 1024 MiB2020-08-30T21:37:40.784518Z 0 [Note] InnoDB: Number of pools: 12020-08-30T21:37:40.784865Z 0 [Note] InnoDB: Using CPU crc32 instructions2020-08-30T21:37:40.789314Z 0 [Note] InnoDB: Initializing buffer pool, total size = 512M, instances = 1, chunk size = 128M2020-08-30T21:37:40.834948Z 0 [Note] InnoDB: Completed initialization of buffer pool2020-08-30T21:37:40.843612Z 0 [Note] InnoDB: If the mysqld execution user is authorized, page cleaner thread priority can be changed. See the man page of setpriority().2020-08-30T21:37:40.859028Z 0 [Note] InnoDB: Highest supported file format is Barracuda.2020-08-30T21:37:40.863176Z 0 [Note] InnoDB: Log scan progressed past the checkpoint lsn 57073942292020-08-30T21:37:40.863221Z 0 [Note] InnoDB: Doing recovery: scanned up to log sequence number 57073942382020-08-30T21:37:40.863231Z 0 [Note] InnoDB: Database was not shutdown normally!2020-08-30T21:37:40.863239Z 0 [Note] InnoDB: Starting crash recovery.2020-08-30T21:37:40.901955Z 0 [Note] InnoDB: Last MySQL binlog file position 0 43848, file name binlog.0000252020-08-30T21:37:41.075805Z 0 [Note] InnoDB: Removed temporary tablespace data file: "ibtmp1"2020-08-30T21:37:41.075860Z 0 [Note] InnoDB: Creating shared tablespace for temporary tables2020-08-30T21:37:41.075952Z 0 [Note] InnoDB: Setting file '/u02/log/3308/iblog/ibtmp1' size to 12 MB. Physically writing the file full; Please wait ...2020-08-30T21:37:41.254016Z 0 [Note] InnoDB: File '/u02/log/3308/iblog/ibtmp1' size is now 12 MB.2020-08-30T21:37:41.255390Z 0 [Note] InnoDB: 96 redo rollback segment(s) found. 96 redo rollback segment(s) are active.2020-08-30T21:37:41.255421Z 0 [Note] InnoDB: 32 non-redo rollback segment(s) are active.2020-08-30T21:37:41.256171Z 0 [Note] InnoDB: Waiting for purge to start2020-08-30T21:37:41.307237Z 0 [Note] InnoDB: 5.7.26 started; log sequence number 57073942382020-08-30T21:37:41.308291Z 0 [Note] Plugin 'FEDERATED' is disabled.2020-08-30T21:37:41.310625Z 0 [Note] InnoDB: Loading buffer pool(s) from /u02/log/3308/iblog/ib_buffer_pool2020-08-30T21:37:41.310785Z 0 [Note] InnoDB: Buffer pool(s) load completed at 2008315:37:41 (/u02/log/3308/iblog/ib_buffer_pool was empty)2020-08-30T21:37:41.314568Z 0 [Note] Recovering after a crash using /u02/log/3308/binlog/binlog2020-08-30T21:37:41.314730Z 0 [Note] Starting crash recovery...2020-08-30T21:37:41.314842Z 0 [Note] Crash recovery finished.2020-08-30T21:37:41.346280Z 0 [Note] Found ca.pem, server-cert.pem and server-key.pem in data directory. Trying to enable SSL support using them.2020-08-30T21:37:41.346337Z 0 [Note] Skipping generation of SSL certificates as certificate files are present in data directory.2020-08-30T21:37:41.349079Z 0 [Warning] CA certificate ca.pem is self signed.2020-08-30T21:37:41.349341Z 0 [Note] Skipping generation of RSA key pair as key files are present in data directory.2020-08-30T21:37:41.350297Z 0 [Note] Server hostname (bind-address): '0.0.0.0'; port: 33082020-08-30T21:37:41.350399Z 0 [Note]- '0.0.0.0' resolves to '0.0.0.0';2020-08-30T21:37:41.350475Z 0 [Note] Server socket created on IP: '0.0.0.0'.2020-08-30T21:37:41.376794Z 0 [Note] Failed to start slave threads for channel ''2020-08-30T21:37:41.397237Z 0 [Note] Event Scheduler: Loaded 0 events2020-08-30T21:37:41.397480Z 0 [Note] /u02/mysql/bin/mysqld: ready for connections.Version: '5.7.26-log'socket: '/u02/run/3308/mysql.sock'port: 3308Source distribution


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