FAQ
i am trying to identify which tables should be moved to diff drives.... i first identified the most used tables... by looking at the data in pg_statio_user_tables.....
and then i did sampling of the io-usage of these tables every 2 mins... to identify which are getting used when....

but the problem is my stats are not getting updated.... they first get updated around 20% done... and then once more at around 70% done.... why is the stats not getting updated more frequently.....

the test application i am using has a 33 min test with lots of read and write....

thx
Himanshu


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  • Himanshu Baweja at Jun 2, 2005 at 10:38 am
    i also noted one more thing... the stats are getting updated only when i do vacuum.... is that wht is supposed to happen... or something is wrong....

    thx
    Himanshu

    Himanshu Baweja wrote:
    i am trying to identify which tables should be moved to diff drives.... i first identified the most used tables... by looking at the data in pg_statio_user_tables.....
    and then i did sampling of the io-usage of these tables every 2 mins... to identify which are getting used when....

    but the problem is my stats are not getting updated.... they first get updated around 20% done... and then once more at around 70% done.... why is the stats not getting updated more frequently.....

    the test application i am using has a 33 min test with lots of read and write....

    thx
    Himanshu


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  • Richard Huxton at Jun 2, 2005 at 11:05 am

    Himanshu Baweja wrote:
    i also noted one more thing... the stats are getting updated only
    when i do vacuum.... is that wht is supposed to happen... or
    something is wrong....
    Hmm - there's something strange going on certainly. Try a couple of
    simple queries on a table and see whether the stats get updated.

    It is possible that during very busy periods the stats don't get
    recorded - that's part of the design.

    --
    Richard Huxton
    Archonet Ltd
  • Tom Lane at Jun 2, 2005 at 3:15 pm

    Richard Huxton writes:
    It is possible that during very busy periods the stats don't get
    recorded - that's part of the design.
    IIRC, backends only ship stats to the collector at transaction commit.
    Or maybe it's at the end of processing a client command. It's certainly
    not continuous.

    regards, tom lane
  • Himanshu Baweja at Jun 2, 2005 at 4:07 pm

    Tom Lane wrote:
    backends only ship stats to the collector at transaction commit.
    Or maybe it's at the end of processing a client command. It's certainly
    not continuous.
    yup that i already know....
    but is there any way to make it do the update more frequently.... 4 times in 30 mins... which makes the stats useless....

    or there is any way to identify the usage of tables... wht i am trying to do is check the table heap_blks_read time to time.... so that i can know how much io is getting used for each table... and during which time... i am doing sampling every 2 min....

    now after i have identified which tables are getting used and when... we can move them to diff partitions for better preformance.....

    is there any way to know the table usage....

    thx
    Himanshu


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