Memory / SGA question
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Thread: Memory / SGA question

  1. #1
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    Memory / SGA question

    We currently run VMS 7.3, Oracle 8.1.7.4 OPS; box has 12gig of memory; SGA around 4gig; new server has 32gig of memory; Oracle is only thing running on servers. Should I increase SGA - Shared Pool and DB_BLOCK_BUFFERS - all my stats look good > 98%. Any suggestions will be appreciated. Is it true that having a too large SGA will cause performance issues?

    Thanks.

  2. #2
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    Maybe you have a 98% hit ratio because of bad SQL -- maybe because of a lot of hash joins. Whatever the reason, stop thinking about buffer cache hit ratio's, and start measuring wait events instead.

    Large SGA used to be a potential cause of problems, but not anymore.
    David Aldridge,
    "The Oracle Sponge"

    Senior Manager, Business Intelligence Development
    XM Satellite Radio
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    Oracle ACE

  3. #3
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    Originally posted by slimdave
    Large SGA used to be a potential cause of problems, but not anymore.
    Well can you please get a link where it says having large SGA is not a problem from 9.x.. Or rather give a logical analogy?

    Well i have seen in some of the instances (9.x) where SGA was more than 3+GB were performing poor (DB Cache was 2.5+GB)... and after reducing it to 1GB DB was performing good.

    Abhay.
    funky...

    "I Dont Want To Follow A Path, I would Rather Go Where There Is No Path And Leave A Trail."

    "Ego is the worst thing many have, try to overcome it & you will be the best, if not good, person on this earth"

  4. #4
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    Originally posted by abhaysk
    Well can you please get a link where it says having large SGA is not a problem from 9.x.. Or rather give a logical analogy?

    Well i have seen in some of the instances (9.x) where SGA was more than 3+GB were performing poor (DB Cache was 2.5+GB)... and after reducing it to 1GB DB was performing good.

    Abhay.
    I recall that the problem was to do with the way that blocks in the sga were "indexed" internally -- if there were too many in memory the it took too long for them to be scanned.
    David Aldridge,
    "The Oracle Sponge"

    Senior Manager, Business Intelligence Development
    XM Satellite Radio
    Washington, DC

    Oracle ACE

  5. #5
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    didnt you face any problems with db cache more the 2+ GB? -- On 9x
    funky...

    "I Dont Want To Follow A Path, I would Rather Go Where There Is No Path And Leave A Trail."

    "Ego is the worst thing many have, try to overcome it & you will be the best, if not good, person on this earth"

  6. #6
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    Originally posted by abhaysk
    didnt you face any problems with db cache more the 2+ GB? -- On 9x
    Who me? Nope
    David Aldridge,
    "The Oracle Sponge"

    Senior Manager, Business Intelligence Development
    XM Satellite Radio
    Washington, DC

    Oracle ACE

  7. #7
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    Originally posted by abhaysk
    didnt you face any problems with db cache more the 2+ GB? -- On 9x
    That was me, Abhay - but it was on 8.1.7.

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