From: Paul <paul@wayr.org>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-performance@postgresql.org
Subject: Re: index & Bitmap Heap Scan
Date: Wed, 29 Aug 2007 10:16:45 +0200
Message-ID: <1188375405.9028.3.camel@thory> (raw)
In-Reply-To: <29055.1188320158@sss.pgh.pa.us>
References: <1188290949.29582.9.camel@thory>
<29055.1188320158@sss.pgh.pa.us>
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@wayr.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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To: pgsql-performance@postgresql.org
Cc: paul@wayr.org, tgl@sss.pgh.pa.us
Subject: Re: index & Bitmap Heap Scan
In-Reply-To: <1188375405.9028.3.camel@thory>
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