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Why SQL Server enable Large Pages?


Why SQL Server enable Large Pages?

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DBA328
DBA328
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From SQL Server error log, i found following information:

[highlight=#ffff11]2009-06-04 12:21:08.16 Server Large Page Extensions enabled.
2009-06-04 12:21:08.16 Server Large Page Granularity: 2097152
2009-06-04 12:21:08.21 Server Large Page Allocated: 32MB [/highlight]

It seems my SQL Server enabels large pages. As my database is OLTP and enable large pages may hurt performance, so i want to turn it off.

My SQL Server is 2005 Enterprise(64 bit) and has 12GB RAM. Service account is local system, trace flag 834 is turned off.

Is there a way to make SQL Server not enable large pages? Currently i don't want to change my service account.

Thanks in advance?

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GilaMonster
GilaMonster
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It's not using large pages, don't worry about that. Without traceflag 834 SQL won't use large pages, it enables the extensions, but that's all.

http://blogs.msdn.com/b/psssql/archive/2009/06/05/sql-server-and-large-pages-explained.aspx <- explained there why you see that entry in the error log.

When SQL's actually using large pages, your error log entry looks like:

2009-06-04 14:20:31.13 Server Large Page Extensions enabled.
2009-06-04 14:20:31.13 Server Large Page Granularity: 2097152
2009-06-04 14:20:31.14 Server Large Page Allocated: 32MB
2009-06-04 14:20:40.03 Server Using large pages for buffer pool.
2009-06-04 14:27:56.98 Server 2048 MB of large page memory allocated.


Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
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DBA328
DBA328
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Thanks Gail. When i query memory utilization by SQL Server, i found AWE allocated about 2GB, working set only taken 88MB ,is it normal?

Query AWE allocated memory:

select
sum(awe_allocated_kb) / 1024 as [AWE allocated, Mb]
from
sys.dm_os_memory_clerks

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GilaMonster
GilaMonster
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How are you seeing the working set? Let me guess, task manager?

Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
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


DBA328
DBA328
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yes, from task manager.

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GilaMonster
GilaMonster
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Never use task manager to check SQL's memory as it will display incorrect values if you have locked pages enabled (Task manager limitation)

Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
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


DBA328
DBA328
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got it. thanks so much.

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