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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: "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: "Heikki Linnakangas" <heikki(at)enterprisedb(dot)com>, "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 17:02:37
Message-ID: 2e78013d0803121002o2b7a8531y1553ce66cb6d1537@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-patchespgsql-performance
On Wed, Mar 12, 2008 at 9:27 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

>
>  I didn't like it; it seemed overly complicated (consider dealing with
>  XID wraparound),

We are talking about subtransactions here. I don't think we support
subtransaction wrap-around, do we ?

> and it would have problems with a slow transaction
>  generating a sparse set of subtransaction XIDs.

I agree thats the worst case. But is that common ? Thats what I
was thinking when I proposed the alternate solution. I thought that can
happen only if most of the subtransactions abort, which again I thought
is not a normal case. But frankly I am not sure if my assumption is correct.

> I think getting rid of
>  the linear search will be enough to fix the performance problem.
>

I wonder if a skewed binary search would help more ? For example,
if we know that the range of xids stored in the array is 1 to 1000 and
if we are searching for a number closer to 1000, we can break the
array into <large,small> parts instead of equal parts and then
search.

Well, may be I making simple things complicated ;-)

Thanks,
Pavan

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

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