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Re: [PERFORM] Very slow (2 tuples/second) sequential scan after bulk insert; speed returns to ~500 tuples/second after commit

From: "Pavan Deolasee" <pavan(dot)deolasee(at)gmail(dot)com>
To: "Heikki Linnakangas" <heikki(at)enterprisedb(dot)com>
Cc: "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "Craig Ringer" <craig(at)postnewspapers(dot)com(dot)au>, pgsql-patches <pgsql-patches(at)postgresql(dot)org>
Subject: Re: [PERFORM] Very slow (2 tuples/second) sequential scan after bulk insert; speed returns to ~500 tuples/second after commit
Date: 2008-03-12 17:26:22
Message-ID: 2e78013d0803121026r227bbebdr5189be193b4a1bf5@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-patchespgsql-performance
On Wed, Mar 12, 2008 at 10:44 PM, Heikki Linnakangas
<heikki(at)enterprisedb(dot)com> wrote:

>
>  Imagine that you start a transaction just before transaction
>  wrap-around, so that the top level XID is 2^31-10. Then you start 20
>  subtransactions. What XIDs will they get? Now how would you map those to
>  a bitmap?
>

Wait. Subtransaction ids are local to a transaction and always start from 1.
See this:

    /*
     * reinitialize within-transaction counters
     */
    s->subTransactionId = TopSubTransactionId;
    currentSubTransactionId = TopSubTransactionId;


>
>  It's not that common to have hundreds of thousands of subtransactions to
>  begin with..

True. But thats the case we are trying to solve here :-)


Thanks,
Pavan

-- 
Pavan Deolasee
EnterpriseDB http://www.enterprisedb.com

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