When Wait Stats Aren’t Enough

Joe Obbish has an example of diagnosing performance problems when wait stats don’t indicate any problems:

In summary, page allocations and page free events rapidly occur, sometimes in an alternating pattern. SQL Server will often free a number of pages just to immediately request allocations for a similar number of pages. If all of the free page events result in returned memory to the OS then the reason for the scalability bottleneck becomes clear. When running the full workaround with 96 concurrent sessions, a total of 341965 page freed operations were performed. Those events freed about 71.3 million pages in total. That amounts to about 584 GB of memory returned to the OS in total, based on the previous assumptions.

This is a great investigation into the depths of debugging in SQL Server.¬† Joe wasn’t able to get a definitive solution to his problem, but he showed us a lot along the way.

Related Posts

What To Watch When Using VSS Snapshots

Erik Darling shows us the wait stats associated with the Volume Shadow Copy Service (VSS): A while back I wrote about the¬†Perils of VSS Snaps. After working with several more clients having similar issues, I decided it was time to look at things again. This time, I wanted blood. I wanted to simulate a slow […]

Read More

Mining The Plan Cache, Query Store, And More

Erin Stellato shows the benefit of digging through the plan cache, Query Store, and third-party performance tool databases (using SentryOne’s SQL Sentry as an example): As much as I love all this extra data, it’s important to note that some information is more relevant for an actual execution plan, versus an estimated one (e.g. tempdb […]

Read More

Categories

July 2018
MTWTFSS
« Jun Aug »
 1
2345678
9101112131415
16171819202122
23242526272829
3031