From: Pavan Deolasee <pavan.deolasee@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Heikki Linnakangas <heikki@enterprisedb.com>
Cc: Craig Ringer <craig@postnewspapers.com.au>
Cc: pgsql-patches <pgsql-patches@postgresql.org>
Subject: Re: [PERFORM] Very slow (2 tuples/second) sequential scan after bulk insert; speed returns to ~500 tuples/second after commit
Date: Wed, 12 Mar 2008 22:32:37 +0530
Message-ID: <2e78013d0803121002o2b7a8531y1553ce66cb6d1537@mail.gmail.com> (raw)
In-Reply-To: <19902.1205337439@sss.pgh.pa.us>
References: <47D505AF.4040101@postnewspapers.com.au>
<23588.1205159638@sss.pgh.pa.us>
<47D54A47.3030608@postnewspapers.com.au>
<47D54DB2.4020405@enterprisedb.com>
<24304.1205162440@sss.pgh.pa.us>
<47D67C3F.1030406@enterprisedb.com>
<5827.1205269597@sss.pgh.pa.us>
<47D7DE12.80700@enterprisedb.com>
<2e78013d0803120847k2e8afbedrc39e29e5194d3c6e@mail.gmail.com>
<19902.1205337439@sss.pgh.pa.us>
On Wed, Mar 12, 2008 at 9:27 PM, Tom Lane <tgl@sss.pgh.pa.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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To: pgsql-performance@postgresql.org
Cc: pavan.deolasee@gmail.com, tgl@sss.pgh.pa.us, heikki@enterprisedb.com, craig@postnewspapers.com.au, pgsql-patches@postgresql.org
Subject: Re: [PERFORM] Very slow (2 tuples/second) sequential scan after bulk insert; speed returns to ~500 tuples/second after commit
In-Reply-To: <2e78013d0803121002o2b7a8531y1553ce66cb6d1537@mail.gmail.com>
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