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Buffer Cache & PLE (Page Life Expectancy) query

  • August 17, 2015 at 8:25 pm

    #303489

    Hi All,

    I'm getting an alert which states that both my Buffer Cache Hit Ratio and PLE are low on one of my SQL Servers though I'm not sure how to correctly check this and I was hoping someone who has experienced this before can help.

    I ran:

    SELECT object_name, counter_name, cntr_value

    FROM sys.dm_os_performance_counters

    WHERE [object_name] LIKE '%Buffer Manager%'

    AND [counter_name] = 'Buffer cache hit ratio'

    Which gives me the Buffer Cache Hit Ratio, cntr_Value of 9 though its constantly dipping between 3-3000 and is never steady and I'm unsure if this is normal.

    I also ran:

    SELECT object_name, counter_name, cntr_value

    FROM sys.dm_os_performance_counters

    WHERE [object_name] LIKE '%Buffer Manager%'

    AND [counter_name] = 'Page life expectancy'

    Which gives me the Page life expectancy of 209061.

    Can you please advise if these values would cause concern and if this is a normal Buffer Cache Hit Ratio? It's constantly dropping from high or low from what I can see. These scripts were pulled from another forum and I'm assuming they're showing the correct values.

  • August 18, 2015 at 1:06 am

    #1820627

    Can't see the image.

    Buffer cache hit ratio is a useless counter. Ignore it.

    PLE can't be judged from a single value. Use Perfmon, set up a counter trace which will run for a day or two and log PLE (the one under buffer node, not the buffer pool), then post the graph here.

    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

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