Tag Archives: mysql recovery

18 Jan

A tale of Corrupt InnoDB table, MySQL crash & recovery

I’m going to narrate you a story that happened around a crashing MyQL, Corrupted InnoDB table and finally the recovery by table restore. We will see how our database administrator detected the issue and what he did to resolve it.

A day in MySQL Database Consultant’s day was taking its shape while a friend called for help.

Friend: Hey, my mysql is crashing and website isn't functioning well. Everything is down. Can you help me?

Our database admin quickly jumps in and checks for the MySQL error log.

        2018-01-01T07:39:03.173398Z 0 [ERROR] InnoDB: Database page corruption on disk or a failed file read of page [page id: space=13701, page number=4603]. You may have to recover from a backup.
        2018-01-01T07:39:03.173428Z 0 [Note] InnoDB: Page dump in ascii and hex (16384 bytes):
        ...
        InnoDB: End of page dump
        2018-01-01T07:39:03.265864Z 0 [Note] InnoDB: Uncompressed page, stored checksum in field1 4187651462, calculated checksums for field1: crc32 4128877936/1194051977, innodb 680941878, none 3735928559, stored checksum in field2 3735928559, calculated checksums for field2: crc32 4128877936/1194051977, innodb 1675940203, none 3735928559,  page LSN 400 3284265879, low 4 bytes of LSN at page end 3284252104, page number (if stored to page already) 4603, space id (if created with >= MySQL-4.1.1 and stored already) 13701
        InnoDB: Page may be an index page where index id is 33515
        2018-01-01T07:39:03.265911Z 0 [Note] InnoDB: Index 33515 is `PRIMARY` in table `nitty-witty`.`flat_address`
        2018-01-01T07:39:03.265919Z 0 [Note] InnoDB: It is also possible that your operating system has corrupted its own file cache and rebooting your computer removes the error. If the corrupt page is an index page. You can also try to fix the corruption by dumping, dropping, and reimporting the corrupt table. You can use CHECK TABLE to scan your table for corruption. Please refer to http://dev.mysql.com/doc/refman/5.7/en/forcing-innodb-recovery.html for information about forcing recovery.
        2018-01-01T07:39:03.265944Z 0 [ERROR] [FATAL] InnoDB: Aborting because of a corrupt database page in the system tablespace. Or,  there was a failure in tagging the tablespace  as corrupt.
        2018-01-01 07:39:03 0x7f5fa0466700  InnoDB: Assertion failure in thread 140048687589120 in file ut0ut.cc line 916
        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/5.7/en/forcing-innodb-recovery.html
        InnoDB: about forcing recovery.
        07:39:03 UTC - mysqld got signal 6 ;
        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.
        Attempting to collect some information that could help diagnose the problem.
        As this is a crash and something is definitely wrong, the information
        collection process might fail.

        key_buffer_size=536870912
        read_buffer_size=16777216
        max_used_connections=6
        max_threads=214
        thread_count=6
        connection_count=6
        It is possible that mysqld could use up to
        key_buffer_size + (read_buffer_size + sort_buffer_size)*max_threads = 7539498 K  bytes of memory
        Hope that's ok; if not, decrease some variables in the equation.

        Thread pointer: 0x0
        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...

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23 Feb

Restore / Recover dropped MySQL database from binary logs

In this post I will share a recovery scenario of a MySQL database restore from the binary logs.

Recently someone accidentally dropped an important MySQL database and the backup was not present!

As we know the the binary log contains DMLs to table data and that’s where our hope lies. Luckily the binary log retention period (expire_logs_days) was set to 30 days and the CREATE DATABASE was still present in the binary logs.

Thus this restore of the dropped MySQL database can be done from extracting respective DMLs point-in-time. Here we will play the binary logs against a temporary MySQL instance and extract the required database.

Let’s begin the recovery of database.
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-- Kedar Vaijanapurkar --