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Re: index & Bitmap Heap Scan

From: Paul <paul(at)wayr(dot)org>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: index & Bitmap Heap Scan
Date: 2007-08-29 08:16:45
Message-ID: 1188375405.9028.3.camel@thory (view raw or flat)
Thread:
Lists: pgsql-performance
Thank you for your answer.
Now i ve to find how to reduce the size of the table.

Paul.

Le mardi 28 août 2007 à 12:55 -0400, Tom Lane a écrit :
> Paul <paul(at)wayr(dot)org> writes:
> > Why in the first case, pgsql uses the "better" index and if i search
> > r_service instead of r_numero pgsql does a "Bitmap Heap scan" first ?
> 
> Given the difference in the number of rows to be fetched, both plan
> choices look pretty reasonable to me.  If you want to experiment,
> you can try forcing the other choice in each case (use enable_indexscan
> and enable_bitmapscan) and see how fast it is, but I suspect the planner
> got it right.
> 
> Beware of cache effects when trying two plans in quick succession ---
> the second one might go faster just because all the data is already
> swapped in.
> 
> 			regards, tom lane
> 


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