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SQL Server 2012 NUMA Node Imbalance – Cont’d

02 Oct

Yesterday, I had posted an issue I been troubleshooting with memory allocation.  That was causing CPU to pin, you can read more about the issue at SQL Server 2012 NUMA Node Imbalance.  Even though I found what was causing it, I didn’t understand the internals well enough to identify the root cause.

Additional testing I discovered this issue is repro on Windows 2008 R2 Server with SQL Server 2012.  It does not seem to fixed that at 4000MB the issue will start; if server is busy, then it can start at a higher value.  In my re-pro test, I found it starting at even 6000MB.

As I said the up front memory allocation and management was contributing to this, however now I am unsure if Locked Pages in Memory is to contribute to this.

However, further insight I learned today.  If this issue exists, you might have Lazy Writer spinning continuously on the effected NUMA node.

Therefore if you execute following T-SQL:

select session_id, wait_type, wait_time, cpu_time, scheduler_id
  from sys.dm_exec_requests
where command = ‘lazy writer’
order by scheduler_id

Look at the output generated, if your Lazy Writer thread is working as normal (aka, only wakes up sometimes) you should see something similar to following:

clip_image002

However if you have this issue the Lazy Writer might look like below:

clip_image002[4]

  • Notice the wait_type has gone to NULL.
  • Notice wait_time has gone to 0 – signal it is not going to sleep like the rest.
  • Notice cpu_time keeps climbing.

Only work around that I know for this currently is, increase the max memory until you see lazy writer stop spinning and processor utilization starts dropping.

 
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Posted by on October 2, 2015 in General topics

 

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