From: Hiroshi Inoue <Inoue@tpf.co.jp>
To: Daniel Kalchev <daniel@digsys.bg>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-hackers@postgresql.org
Subject: Re: again on index usage
Date: Wed, 09 Jan 2002 18:45:22 +0900
Message-ID: <3C3C1132.E51307CF@tpf.co.jp> (raw)
References: <200201090745.JAA15141@dcave.digsys.bg>
Daniel Kalchev wrote:
>
> >>>Tom Lane said:
> > Daniel Kalchev <daniel@digsys.bg> writes:
> > > Same result (sorry, should have included this originally):
> >
> > >>> If you say "set enable_seqscan to off", does that change the plan?
> >
> > > Aggregate (cost=100359.71..100359.71 rows=1 width=8)
> > > -> Index Scan using iplog_gate200112_ipdate_idx on iplog_gate200112
> > > (cost=0.00..100217.52 rows=56873 width=8)
> >
> > So, what we've got here is a difference of opinion: the planner thinks
> > that the seqscan will be faster. How many rows are actually selected
> > by this WHERE clause? How long does each plan actually take?
> >
> > regards, tom lane
>
> 3-5 minutes with sequential scan; 10-15 sec with index scan. The query returns
> 4062 rows. Out of ca 1700000 rows.
>
> With only the datetime constraints (which relates to the index), the number of
> rows is 51764.
The planner estimates 56873 rows. It seems not that bad.
A plausible reason is your table is nearly clustered
as to ipdate.
regards,
Hiroshi Inoue
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To: pgsql-hackers@postgresql.org
Cc: Inoue@tpf.co.jp, daniel@digsys.bg, tgl@sss.pgh.pa.us
Subject: Re: again on index usage
In-Reply-To: <3C3C1132.E51307CF@tpf.co.jp>
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