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Re: planner/optimizer question

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 (view raw or flat)
Thread:
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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