From: | Josh Berkus <josh(at)agliodbs(dot)com> |
---|---|
To: | "Gary Doades" <gpd(at)gpdnet(dot)co(dot)uk>, pgsql-performance(at)postgresql(dot)org |
Subject: | Re: planner/optimizer question |
Date: | 2004-04-29 20:54:33 |
Message-ID: | 200404291354.33304.josh@agliodbs.com |
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Lists: | pgsql-performance |
Gary,
> In this example the statistics don't matter. The plans used were the same
for
> MSSQL and Postgres. I was trying to eliminate the difference in plans
> between the two, which obviously does make a difference, sometimes in
> MSSQL favour and sometimes the other way round. Both systems, having
> decided to do the same index scan, took noticably different times. The
> Postgres database was fully vacuumed and analysed anyway.
It's also quite possble the MSSQL simply has more efficient index scanning
implementation that we do. They've certainly had incentive; their storage
system sucks big time for random lookups and they need those fast indexes.
(just try to build a 1GB adjacency list tree on SQL Server. I dare ya).
Certainly the fact that MSSQL is essentially a single-user database makes
things easier for them. They don't have to maintain multiple copies of the
index tuples in memory. I think that may be our main performance loss.
--
-Josh Berkus
Aglio Database Solutions
San Francisco
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