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今天就跟大家聊聊有关如何进行 mysql 性能测试库的 CRASH 恢复，可能很多人都不太了解，为了让大家更加了解，丸趣 TV 小编给大家总结了以下内容，希望大家根据这篇文章可以有所收获。

环境:
OS: Linux als_qa_rhel5.3 2.6.18-128.el5 #1 SMP Wed Dec 17 11:41:38 EST 2008 x86_64 x86_64 x86_64 GNU/Linux
MYSQL:MySQL-server-enterprise-gpl-5.0.68-0.rhel4.x86_64[@more@]

一个 MYSQL 的性能测试数据库, 在高压力测试过程中, 忽然 CRASH,
以下为 MYSQL 重启时的,LOG 日志:

——————————————————–
090716 09:31:02  mysqld started
InnoDB: Log scan progressed past the checkpoint lsn 32 2512592438
090716  9:31:03  InnoDB: Database was not shut down normally!
InnoDB: Starting crash recovery.
InnoDB: Reading tablespace information from the .ibd files…
InnoDB: Restoring possible half-written data pages from the doublewrite
InnoDB: buffer…
InnoDB: Doing recovery: scanned up to log sequence number 32 2517835264
InnoDB: Doing recovery: scanned up to log sequence number 32 2523078144
InnoDB: Doing recovery: scanned up to log sequence number 32 2528321024
InnoDB: Doing recovery: scanned up to log sequence number 32 2533563904
InnoDB: Doing recovery: scanned up to log sequence number 32 2538806784
InnoDB: Doing recovery: scanned up to log sequence number 32 2544049664
InnoDB: Doing recovery: scanned up to log sequence number 32 2549292544
InnoDB: Doing recovery: scanned up to log sequence number 32 2554535424
InnoDB: Doing recovery: scanned up to log sequence number 32 2559778304
InnoDB: Doing recovery: scanned up to log sequence number 32 2565021184
InnoDB: Doing recovery: scanned up to log sequence number 32 2570264064
InnoDB: Doing recovery: scanned up to log sequence number 32 2575506944
InnoDB: Doing recovery: scanned up to log sequence number 32 2580749824
InnoDB: Doing recovery: scanned up to log sequence number 32 2585992704
InnoDB: Doing recovery: scanned up to log sequence number 32 2591235584
InnoDB: Doing recovery: scanned up to log sequence number 32 2596478464
InnoDB: Doing recovery: scanned up to log sequence number 32 2601721344
InnoDB: Doing recovery: scanned up to log sequence number 32 2606964224
InnoDB: Doing recovery: scanned up to log sequence number 32 2612207104
InnoDB: Doing recovery: scanned up to log sequence number 32 2617449984
InnoDB: Doing recovery: scanned up to log sequence number 32 2622692864
InnoDB: Doing recovery: scanned up to log sequence number 32 2627935744
InnoDB: Doing recovery: scanned up to log sequence number 32 2633088581
090716  9:31:05  InnoDB: Starting an apply batch of log records to the database…
InnoDB: Progress in percents: 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99
InnoDB: Apply batch completed
InnoDB: Last MySQL binlog file position 0 22007701, file name ./mysql-bin.000149
090716  9:31:49  InnoDB: Started; log sequence number 32 2633088581
090716  9:31:49 [Note] Recovering after a crash using mysql-bin
090716  9:31:49 [Note] Starting crash recovery…
090716  9:31:49 [Note] Crash recovery finished.
090716  9:31:49 [Note] /usr/sbin/mysqld: ready for connections.
Version: 5.0.68-enterprise-gpl-log  socket: /tmp/mysql.sock  port: 3306  MySQL Enterprise Server (GPL)
090716  9:31:59InnoDB: Assertion failure in thread 1177917760 in file btr0cur.c line 3606
InnoDB: Failing assertion: extern_len – part_len == 0
InnoDB: We intentionally generate a memory trap.
InnoDB: Submit a detailed bug report to http://bugs.mysql.com.
InnoDB: If you get repeated assertion failures or crashes, even
InnoDB: immediately after the mysqld startup, there may be
InnoDB: corruption in the InnoDB tablespace. Please refer to
InnoDB: http://dev.mysql.com/doc/refman/5.0/en/forcing-recovery.html
InnoDB: about forcing recovery.
090716  9:31:59 – mysqld got signal 11 ;
This could be because you hit a bug. It is also possible that this binary
or one of the libraries it was linked against is corrupt, improperly built,
or misconfigured. This error can also be caused by malfunctioning hardware.
We will try our best to scrape up some info that will hopefully help diagnose
the problem, but since we have already crashed, something is definitely wrong
and this may fail.

key_buffer_size=335544320
read_buffer_size=1048576
max_used_connections=2
max_connections=1000
threads_connected=2
It is possible that mysqld could use up to
key_buffer_size + (read_buffer_size + sort_buffer_size)*max_connections = 2375680 K
bytes of memory
Hope that s ok; if not, decrease some variables in the equation.

thd=(nil)
Attempting backtrace. You can use the following information to find out
where mysqld died. If you see no messages after this, something went
terribly wrong…
frame pointer is NULL, did you compile with
-fomit-frame-pointer? Aborting backtrace!
The manual page at http://dev.mysql.com/doc/mysql/en/crashing.html contains
information that should help you find out what is causing the crash.

Number of processes running now: 0
090716 09:31:59  mysqld restarted
————————————————————–

在日志中我们看到,INNODB recovery 成功后, 并显示
090716  9:31:49 [Note] /usr/sbin/mysqld: ready for connections.
这是正常的情况, 但紧接着, 就重新启动了.
这时, 客户端连接不上.
但查看 MYSQL 进程, 却又还在.
用 SERVICE MYSQL STOP 无法停止库. 只能用 KILL - 9 来杀掉.

目前来看, 只能是猜测遇到 BUG.(这个版本在其他库跑得比较正常)
而且这样的 BUG 不能重现. 有可能只有在高压力的情况下才会出现.

遇到这样的情况, 我们最重要的是把数据备份出来.
所以尽可能把库打开, 把数据备份出来.

比较幸运的事. 这一次数据库 INNODB 表空间没有被破坏.
有 MY.CNF 配置文件中加入:
[mysqld]
innodb_force_recovery = 2

数据库顺利打开. 这时赶紧用 MYSQLDUMP 做个全库导出.

然后把库全部删除, 重新安装 MYSQL.

最后把库全部导入 …

虽然库是恢复了. 但想找找原因. 为什么 innodb_force_recovery = 2 就可以打开了呢.
从 http://dev.mysql.com/doc/refman/5.0/en/forcing-recovery.html 上得到:

1 (SRV_FORCE_IGNORE_CORRUPT)

Let the server run even if it detects a corrupt page. Try to make SELECT * FROM tbl_name jump over corrupt index records and pages, which helps in dumping tables.

2 (SRV_FORCE_NO_BACKGROUND)

Prevent the main thread from running. If a crash would occur during the purge operation, this recovery value prevents it.

3 (SRV_FORCE_NO_TRX_UNDO)

Do not run transaction rollbacks after recovery.

4 (SRV_FORCE_NO_IBUF_MERGE)

Prevent insert buffer merge operations. If they would cause a crash, do not do them. Do not calculate table statistics.

5 (SRV_FORCE_NO_UNDO_LOG_SCAN)

Do not look at undo logs when starting the database: InnoDB treats even incomplete transactions as committed.

6 (SRV_FORCE_NO_LOG_REDO)

Do not do the log roll-forward in connection with recovery.

其中 2 是说: 如果 purge operation 导致 CRASH, 那么这个设置就会生效.

这里的 purge operation 到底是什么样的操作.   搜寻中 …………

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