# pt-table-checksum, replication filters

**URL:** <https://forums.percona.com/t/pt-table-checksum-replication-filters/2404>\
**Category:** Other Tools\
**Created:** [April 3, 2012, 1:11pm UTC](https://forums.percona.com/t/pt-table-checksum-replication-filters/2404 "2012-04-03T13:11:41Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![hullsean](https://avatars.discourse-cdn.com/v4/letter/h/4da419/32.png) [@hullsean](https://forums.percona.com/u/hullsean)\
**Post date:** [April 3, 2012, 1:11pm UTC](https://forums.percona.com/t/pt-table-checksum-replication-filters/2404/1 "2012-04-03T13:11:41Z")

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Hi all,

I’m getting an error with pt-table-checksum.

Cannot checksum with --replicate because replication filters are set on these hosts:  
P=3306,S=/var/lib/mysql/mysql.sock,h=localhost,p=…,u=root  
replicate\_ignore\_table = prod\_thr.semaphore  
P=3306,S=/var/lib/mysql/mysql.sock,[h=pldnyi05.pgmedia.org](http://h=pldnyi05.pgmedia.org),p= …,u=root  
replicate\_ignore\_table = prod\_thr.semaphore  
P=3306,S=/var/lib/mysql/mysql.sock,h=10.17.33.72,p=…,u=roo t  
replicate\_ignore\_table = prod\_aw.semaphore  
Please read the --check-replication-filters documentation to learn how to solve this problem. at /usr/bin/pt-table-checksum line 5315.

From the docs it is clear that this is caused by a replication filter. Yes I just added one for a SINGLE table, the drupal semaphore table. It’s MyISAM and periodically (maybe once a month or so) we find replication dying due to this table. Since it doesn’t need to replicate, we use a replicate\_ignore\_table option in our my.cnf file.

Unfortunately it has broken our pt-table-checksum checks, which I _REALLY_ want to have in place.

How risky is this --nocheck-replication-filters flag? What exactly does it do?

If the _ONLY_ replication filter I have in place is this one rule to ignore the semaphore table, could that introduce serious problems? Obviously I don’t want replication to break because of pt-table-checksum gathering on the master.

Thoughts?

Thx in advance!

-Sean

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**Author:** ![xaprb](https://avatars.discourse-cdn.com/v4/letter/x/49beb7/32.png) [@xaprb](https://forums.percona.com/u/xaprb)\
**Post date:** [April 3, 2012, 3:02pm UTC](https://forums.percona.com/t/pt-table-checksum-replication-filters/2404/2 "2012-04-03T15:02:15Z")

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The option is there to scare you into making sure you will be safe. We’d rather you are scared than that you blame us for breaking replication 🙂

Without knowing exact details about your replication topology I can’t give firm advice, but you shouldn’t have any trouble knowing if this is unsafe. You should be able to pass the --ignore-tables option to the tool and then disable the check.

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**Author:** ![hullsean](https://avatars.discourse-cdn.com/v4/letter/h/4da419/32.png) [@hullsean](https://forums.percona.com/u/hullsean)\
**Post date:** [April 4, 2012, 1:08pm UTC](https://forums.percona.com/t/pt-table-checksum-replication-filters/2404/3 "2012-04-04T13:08:55Z")

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Thx Baron. For the tool and the reply!

I have no idea how you find the time to do all the stuff you do.

PS: Just received your new book from Amazon. I’m 150 pages into it. Full of useful nuggets on every page. Will have a review of it posted soon enough.

Cheers!  
-Sean