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Performance issue due to high memory usage Expand / Collapse
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Posted Thursday, January 03, 2013 8:17 PM
Old Hand

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All,

We have some performance issue..SQL server is running very slow due to high memory usage..this is a 2 node active/passive cluster. Only 1 instance is running, no other apps.

Total 56GB RAM and 46GB is allocated SQL. No blocking, no open transactions, no long running queries found.

Is there any other way to release the memory? Or how can we find why SQL server is using high memory?

What are some of the causes of using high memory? Someone with experience in performance tuning, please advise.

Thanks,
SueTons


Regards,
SQLisAwe5oMe.
Post #1402644
Posted Thursday, January 03, 2013 10:09 PM


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How many connections? Do you have a high volume of transactions or jobs running currently?



Jason AKA CirqueDeSQLeil
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Post #1402673
Posted Friday, January 04, 2013 12:30 AM
Say Hey Kid

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Can you elaborate on what you mean by SQL is running slow? Specifics? You state that it is slow but there are no long running queries found.

Joie Andrew
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Post #1402723
Posted Friday, January 04, 2013 2:24 AM


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SQLCrazyCertified (1/3/2013)
We have some performance issue..SQL server is running very slow due to high memory usage.


Are you sure that high memory usage is causing SQL to run slow? Cause, not correlation?

Is there any other way to release the memory? Or how can we find why SQL server is using high memory?

What are some of the causes of using high memory? Someone with experience in performance tuning, please advise.


Normal, expected behaviour. SQL uses as much memory as it is allowed to use to cache data and plans to avoid slow disk access and expensive plan recompilations. SQL will use up to the max it is allowed and that is perfectly fine. You typically want SQL to use lots of memory as it allows for efficient caching.



Gail Shaw
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Post #1402757
Posted Friday, January 04, 2013 4:15 AM


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What are your top 5 wait stats from sys.dm_os_wait_stats? If they are not memory related, then I doubt memory is the cause of the slow performance.

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Post #1402793
Posted Friday, January 04, 2013 9:11 AM
Old Hand

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SQLRNNR, There are only 50 active connections.....so, I don't think this is the issue.

Joie Andrew, Had complains that everything is running slow and I coudn't find anything else other than SQL using all the memory which is allocated to it.

GilaMonster, I am not 100% sure if it's only memory related, however, I am stuck as to what's the next step....not an exper on performance tuning.

Grant Fritchey, I did select * from sys.dm_os_wait_stats, now which column should I focus.

I really appreciate all of you for giving me valid inputs as to where/what should I be checking. Could this be a CPU issue as well?

Thanks,
SueTons.




Regards,
SQLisAwe5oMe.
Post #1402948
Posted Friday, January 04, 2013 9:24 AM


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It could be anything. Shotgun tuning however won't help.

Chapter 1: http://www.simple-talk.com/books/sql-books/troubleshooting-sql-server-a-guide-for-the-accidental-dba/ Identify the problem, then consider what the potential solution is.



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Post #1402953
Posted Friday, January 04, 2013 6:33 PM
Old Hand

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Is there any other way to release the memory? Or how can we find why SQL server is using high memory?

What are some of the causes of using high memory? Someone with experience in performance tuning, please advise.


Normal, expected behaviour. SQL uses as much memory as it is allowed to use to cache data and plans to avoid slow disk access and expensive plan recompilations. SQL will use up to the max it is allowed and that is perfectly fine. You typically want SQL to use lots of memory as it allows for efficient caching.
[/quote]

Gail,

You mentioned that SQL using all of it's memory which is allocated to it is a normal behavior, if this is true, when does the SQL release the memory?

I know it won't release the memory to OS, but when does SQL gets more memory to do other work/processes. Please advise.

SueTons.


Regards,
SQLisAwe5oMe.
Post #1403179
Posted Saturday, January 05, 2013 1:46 AM


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SQLCrazyCertified (1/4/2013)
You mentioned that SQL using all of it's memory which is allocated to it is a normal behavior, if this is true, when does the SQL release the memory?


When the OS signals that it's under memory pressure or when SQL shuts down.

I know it won't release the memory to OS, but when does SQL gets more memory to do other work/processes. Please advise.


Get more memory? If it's allocated up to max server memory then it won't allocate more.



Gail Shaw
Microsoft Certified Master: SQL Server 2008, MVP
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

Post #1403202
Posted Saturday, January 05, 2013 12:50 PM
Old Hand

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GilaMonster (1/5/2013)
SQLCrazyCertified (1/4/2013)
You mentioned that SQL using all of it's memory which is allocated to it is a normal behavior, if this is true, when does the SQL release the memory?


When the OS signals that it's under memory pressure or when SQL shuts down.

I know it won't release the memory to OS, but when does SQL gets more memory to do other work/processes. Please advise.


Get more memory? If it's allocated up to max server memory then it won't allocate more.


So, if I understand you correctly, if SQL uses all the memory which is allocated to it, then SQL will not have enough memory to work on other outstanding processes, so, in this scenario can we say that memory is the issue for performance issues? If that's the case how can you say it's the normal expected behavior?

SueTons.


Regards,
SQLisAwe5oMe.
Post #1403274
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