I'm using MySQL 5.6 with about 5 databases on linux. I have scheduled daily full backups using mysqldump. All databases use InnoDB engine.

What I observe is that the backup size seems to vary everyday. This would make sense if the backup size keeps increasing but what is happening is randomly the backup size goes down.

I have confirmed with application teams that do not purge or delete data and I understand mysqldump is a logical representation of the data but how can backup size decrease randomly when there is no delete/truncate of data?

  • Do you dump just the 5 user databases, or do you dump the system databases, too? Glance through the dump file.
    – Rick James
    Aug 18, 2016 at 1:25

1 Answer 1


How much does the size go down by when it does? If it is by a small amount it could be users deleting data (or replacing it by smaller data) during normal operation.

Are you compressing the dumps and looking at the size of the compressed files? The data may not always come out in exactly the same order in the dump and this could affect the compresibilty of it.

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