From: | Hannu Krosing <hannu(at)tm(dot)ee> |
---|---|
To: | bruc(at)acm(dot)org |
Cc: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Re: Performance degradation in PostgreSQL 7.1beta3 vs |
Date: | 2001-01-17 20:10:32 |
Message-ID: | 3A65FC38.3A749B4D@tm.ee |
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Thread: | |
Lists: | pgsql-hackers |
"Robert E. Bruccoleri" wrote:
>
> >
> > what are the cost estimates when you run explain with seqscan disabled ?
> > do => SET ENABLE_SEQSCAN TO OFF;
> > see:
> > (http://www.postgresql.org/devel-corner/docs/admin/runtime-config.htm#RUNTIME-CONFIG-OPTIMIZER)
>
> Here's the result from EXPLAIN:
>
> Aggregate (cost=19966.21..19966.21 rows=1 width=0)
> -> Index Scan using comparisons_4_code on comparisons_4 (cost=0.00..19947.73 rows=7391 width=0)
>
> The estimates are too high.
You could try experimenting with
SET RANDOM_PAGE_COST TO x.x;
from the page above
RANDOM_PAGE_COST (floating point)
Sets the query optimizer's estimate of the cost of a
nonsequentially fetched disk page.
this is measured as a multiple of the cost of a sequential page
fetch.
Note: Unfortunately, there is no well-defined method of
determining ideal values for
the family of "COST" variables that were just described. You are
encouraged to
experiment and share your findings.
-------------
Hannu
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