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Performance Issue - Memory Expand / Collapse
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Posted Friday, March 8, 2013 4:33 AM
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Hi All

On one of my SQL Servers, I am noticing what I think is memory pressure

PLE is +-100
Buffer Cache Hit Ratio is 99%

I would think that with a low PLE comes a low Buffer Cache Hit Ratio??

I am noticing PAGEIOLATCH waits on top of my wait_stats list - I'm assuming that this ties into the low PLE.

Server: SQL 2008 ENT on Windows 2008 ENT
Memory: Server memory - 50GB, Memory allocated to SQL - 42GB
Locked pages in memory is set

I have had some user complaints about performance

What is the recommended method to approach this

Thanks
Post #1428511
Posted Friday, March 8, 2013 3:13 PM


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Why BCHR doesn't normally matter: https://www.simple-talk.com/sql/database-administration/great-sql-server-debates-buffer-cache-hit-ratio/

As for PLE drops, you can trace for queries running when the PLE bottoms out to figure what is happening in the database when it drops. Many times it's a nasty select for a report that requires a ton of data which displaces a large percentage of the buffer pool. You can also look for external pressure, i.e. memory set trims imposed on SQL Server by Windows. You can find notices for those in the SQL Error Log.


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Post #1428783
Posted Monday, March 11, 2013 12:24 AM
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Thanks OPC

During times of the low PLE - I am noticing some nasty selects coming through.

I suppose my next move is to try and optimize the queries ?

Thanks
Post #1429095
Posted Monday, March 11, 2013 3:14 AM


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Yes. Optimise queries, tune indexes.


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

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