Help with wait type CHECK_TABLES_THREAD_BARRIER

Question

I have a 2016 SQL Server freshly built - 13.0.5149.0 - OS 2016 (Microsoft Windows NT 6.3 (14393)). The environment is VMWare. No SQL Server HA configuration.

It has a problem where CheckDB "stops" with a wait type of CHECK_TABLES_THREAD_BARRIER. It has happened twice on 2 different databases. I don't see much listed on online resources for what to do with this wait. Microsoft lists "TBD" on information. This is a non production proof of concept environment for an upgrade.

Can anyone provide any insight or next steps?

Answer 1

The wait types are sometimes sort of self-documenting, in this case I would piece together that something is causing CHECKDB to use too many threads. One way to attempt to minimize or eliminate this is to restrict CHECKDB to using a single core with the MAXDOP option:

DBCC CHECKDB ('database') WITH MAXDOP = 1;

I have other ideas for minimizing impact of CHECKDB here (granted it was written long before the MAXDOP option was added, so I need to update the post):

• Minimizing the impact of DBCC CHECKDB : DOs and DON'Ts

If you want an official answer from Microsoft, I suspect you'll have to open a support case. It may be that there is a bug leading to this symptom, in which case the support call will be free, but I wouldn't go through that just to get the explanation of what CHECK_TABLES_THREAD_BARRIER means, especially when you know you have a viable workaround.

Answer 2

Although I don't have any info on this yet in my waits library (will be fixed soon), you're likely hitting this hang when CHECKDB has hit an error state and it waiting for the various threads to finish running.

This is a rare, known issue that Microsoft is investigating but as yet has not identified or fixed.

Thanks