# pt-table-checksum not detecting diff

**URL:** <https://forums.percona.com/t/pt-table-checksum-not-detecting-diff/5111>\
**Category:** Percona Toolkit\
**Created:** [September 27, 2016, 8:31am UTC](https://forums.percona.com/t/pt-table-checksum-not-detecting-diff/5111 "2016-09-27T08:31:06Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![nhadsall](https://sea1.discourse-cdn.com/flex019/user_avatar/forums.percona.com/nhadsall/32/5698_2.png) [@nhadsall](https://forums.percona.com/u/nhadsall)\
**Post date:** [September 27, 2016, 8:31am UTC](https://forums.percona.com/t/pt-table-checksum-not-detecting-diff/5111/1 "2016-09-27T08:31:06Z")

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I have a very simple setup: 1 master with 2 replicas. I turned one of the replicas off and changed a row on the master. I ran

```auto
pt-table-checksum --databases=db_main --user=user --pass='pass'

```

but do not get and diffs. I read the documentation a few times, but can’t seem to find what I might be missing.

Thanks!

---

<div class="post-metadata">

**Author:** ![Barrett](https://sea1.discourse-cdn.com/flex019/user_avatar/forums.percona.com/barrett/32/15734_2.png) [@Barrett](https://forums.percona.com/u/Barrett)\
**Post date:** [September 27, 2016, 11:14am UTC](https://forums.percona.com/t/pt-table-checksum-not-detecting-diff/5111/2 "2016-09-27T11:14:58Z")

</div>

If the replica that you turned off is still down, then pt-table-checksum is not going to be able to check it.  
Once you turn it back on, it will likely replicate and you will be unable to view differences.  
You can test this by adding a delay to your replication setup, or change a row on a replica and run the checksum again.

I hope this helps.