17.2 Working Around Corruption Problems

Sometimes the operating system or the hardware can corrupt a data file page at a location that does not cause a database error, but prevents mysqlbackup from completing:

170225 10:46:18 PCR1    INFO: Re-reading page at offset 0 in D:/temp/5.7_source/test/emp2.ibd
170225 10:46:18 PCR1    INFO: Re-reading page at offset 0 in D:/temp/5.7_source/test/emp2.ibd
...
170225 10:46:26 PCR1 ERROR: Page at offset 0 in D:/temp/5.7_source/test/emp2.ibd seems corrupt!

A corruption problem can have different causes. Here are some suggestions for dealing with it:

• The problem can occur if the MySQL server is too busy. Before trying other solutions, you might want to perform the backup again using some non-default settings for the following mysqlbackup options:

  • --page-reread-time=MS. Try set the value to, for example, “0.05”, for faster rereads during checksum failures.

  • --page-reread-count=retry_limit. Try set the value to, for example, “1000”, to allow more rereads during checksum failures before MySQL Enterprise Backup gives up and throws an error.

• Scrambled data in memory can cause the problem even though the data on disk is actually uncorrupted. Reboot the database server and the storage device to see if the problem persists.

• If the problem persists after the database server and the storage device have been restarted, you might really have a corruption on your disk. You might consider restoring data from an earlier backup and "roll forward" the recent changes to bring the database server back to its current state.

• If you want to make MySQL Enterprise Backup finish a backup anyway before you go and investigate the root cause of the issue, you can rewrite the checksum values on the disk by running the innochecksum utility on the server:

  innochecksum --no-checksum --write=crc32

  The option --no-checksum disable the verification function of the tool, and the option --write=crc32 makes innochecksum rewrite the checksum values on the disk.

IMPORTANT: Do not treat corruption problems as a minor annoyance. Find out what is wrong with the system that causes the corruption—however, such troubleshooting is beyond the scope of this manual.