Comments on: Resyncing table on MySQL Slave

By: peter

peter — Tue, 01 Jul 2008 21:14:07 +0000

Sheeri,

You can use MySQLHotCopy however this makes the process much more elaborate if you have traffic flowing as you need to ensure the table is “synced” at same point in time in master and slave which can be hard to guaranty for complex replication topologies.

The mk-table-sync is nice tool as I mentioned though it is not always installed. If you just want to do things once using Stock MySQL tools that is what I mainly wrote about.

Thanks for feedback

By: Sheeri

Sheeri — Tue, 01 Jul 2008 09:46:48 +0000

Don’t forget that you can also use mysqlhotcopy if the table is MyISAM. This option is not given, but many folks still use MyISAM tables.

Also, you have not mentioned how one might determine that the slave is out of sync. There may be some data sync issues you discover through replication errors; or perhaps you use mk-table-sync or mk-table-checksum, or MySQL’s built-in CHECKSUM() function.

At any rate, if it’s a small table, mk-table-sync is actually the best tool anyway, as with one command it will checksum the table, determine differences, and can either write statements to a file to fix the slave, or actually enact the differences. This takes a longer time and will (read) lock the master for a longer time if the table is bigger.

Still, this is a good reference for folks who cannot have ma’atkit on their system for whatever reason.

By: peter

peter — Mon, 30 Jun 2008 17:03:10 +0000

James,

Indeed TRUNCATE does not work with LOCKED table.

Suhaib,

Reloading the table is pretty much only way with logical level replication.

You can also use mysqldump to reload the table. What I described here just gives you a bit more control about data visibility.

By: Suhaib

Suhaib — Mon, 30 Jun 2008 10:05:54 +0000

James, so is the dumping & reloading from file the only way to make out-of-sync slave synchronized.

By: ak47

ak47 — Mon, 30 Jun 2008 09:52:57 +0000

James:
w/ truncate you would probably run into http://bugs.mysql.com/bug.php?id=20667 which is easily demonstrable.

By: James Cohen

James Cohen — Mon, 30 Jun 2008 09:43:57 +0000

@Suhaib – The INSERT/SELECT would work on the master but (assuming you’re using statement based replication) would just reload the original (out of sync) data on the slave.

@Peter – any reason why you use DELETE in place of TRUNCATE in the original example?

By: Suhaib

Suhaib — Mon, 30 Jun 2008 08:42:40 +0000

Why not use INSERT-SELECT query instead of dumping table & then reloading it again. I think INSERT-SELECT query works quite fast compare to this.

By: Scott

Scott — Mon, 30 Jun 2008 06:08:29 +0000

Depending on the storage engine, you may need to be careful with the auto-increment variable with the first method. Better to manually save & restore that value as well.