CODEWITHSUNDEEP
sql-servert-sqlsql-server-2005
usr
usr

Reputation: 171206

What is "MISCELLANEOUS" in sys.dm_os_wait_stats?

Checking sys.dm_os_wait_stats looks like this for me:

enter image description here

What does MISCELLANEOUS mean? The docs don't say anything. The wait stats had just been cleared. MISCELLANEOUS is increasing steadily over time.

Upvotes: 2

Views: 13743

Answers (2)

Rahul
Rahul

Reputation: 77896

In addition to what @Aaron have already explained, this doc mentions that it's future compatibility is not guaranteed.

MISCELLANEOUS

Identified for informational purposes only. Not supported. Future compatibility is not guaranteed.

Upvotes: 0

Aaron Bertrand
Aaron Bertrand

Reputation: 280431

You can probably ignore it. If this is one of your top waits, your system is most likely doing just fine (exception below).

From The SQL Server Wait Type Repository...

This really should be called "Not Waiting".

This may have been used in SQL 2000 but for 2005/2008, it is not used for any valid wait. It is simply the default wait in a list and isn't used to indicate any real waiting. This type shows up twice in sys.dm_os_wait_stats in SQL 2008 but the "other" instance is an older unused wait type in the code. We should be able to remove it.

On the other hand, if you are using NEWSEQUENTIALID() or CLR, you may also pay attention to this note, from the late Ken Henderson's SQL Server 2005 Waiting and Blocking Issues:

In SQL Server 2005, most of these unusual cases have been converted to more descriptive wait types, but several are still grouped under the MISCELLANEOUS wait type. Of these, two are worth mentioning. The first is synchronization for the NEWSEQUENTIALID built-in function. The other is synchronization of CLR assembly loads. Because these usages get clumped with each other in the MISCELLANEOUS bucket, it is not possible to differentiate between them without examining the statements being executed by the sessions.

This article is a little older, so it may be that the CSS blog post has knowledge about changes that occurred in service packs or 2008+ that Ken simply wasn't armed with at the other time (in other words, this may not necessarily be true anymore for the build of SQL Server 2005 you're running).

Since the wait type is not exactly well-documented, it's not very clear when and how certain wait types get promoted out of this bucket, but I think it's clear that over time there are less and less "meaningful" delays being captured here.

Upvotes: 6

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