Comments on: On hot backups

By: Mark Callaghan

Mark Callaghan — Tue, 19 Apr 2011 04:14:27 +0000

Algorithm is obvious implies comments are not needed? Very funny to some, very annoying to others trying to debug a continuous crash that occurs during crash recovery.

Obscure and obfuscated open-source software becomes less interesting to me with each passing day.

By: Ryan Huddleston

Ryan Huddleston — Mon, 31 May 2010 17:25:10 +0000

Just wanted to point out that xtrabackup/xtradb already has the feature of moving hot backup from on instance to another without restarting mysql

See “Restoring a single .ibd file” section here (same can apply to one whole DB):

http://www.percona.com/docs/wiki/percona-xtrabackup:xtrabackup_manual

By: Domas Mituzas

Domas Mituzas — Thu, 20 May 2010 08:12:08 +0000

@Heikki, thanks for update and clarification – though I still think that the documentation levels in that file are way under InnoDB standards in other parts, and some of information I’d love to find in comments there was missing. I’ll update the post.

By: Heikki Tuuri

Heikki Tuuri — Mon, 10 May 2010 15:16:08 +0000

Domas,

you are claiming:
”
Few years ago I was looking at crash recovery code, and realized that InnoDB has removed all the comments from the code, related to replay of transaction log. Judging by high quality of comments in the remaining codebase, I realized that it was all done to obscure any efforts to build another InnoDB hot backup solution – competitor to first Innobase standalone offering.
”
I am not aware of any comments that would have been removed. InnoDB was published in the MySQL-3.23.35 source release in March 2000. At that time I did not have any plans for a Hot Backup product. If you look at the source code of MySQL-4.0.10 a couple of years later, you notice that comments have not been removed from log0recv.c. Instead, that file contains a couple of additional functions that are used by InnoDB Hot Backup.

The reason why log0recv.c is quite scarcely commented in 3.23.35 is that the algorithm is relatively straightforward and did not require extensive commenting.

Best regards,

Heikki Tuuri