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Re: PostgreSQL does CAST implicitely between int and a domain derived from int

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>
Cc: pgsql-performance(at)postgresql(dot)org, Jean-Michel Pouré <jm(at)poure(dot)com>
Subject: Re: PostgreSQL does CAST implicitely between int and a domain derived from int
Date: 2009-08-27 17:35:02
Message-ID: 603c8f070908271035h2dbdf1f0heafa475e560a8118@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
2009/8/27 Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>:
> It is *possible* that if you boost your default_statistics_target and
> run ANALYZE (or VACUUM ANALYZE), it will recognize that it isn't a
> good idea to read backwards on that index.  I would try it and see, if
> that's practical for you.

I notice this in one of the plans:

->  Bitmap Index Scan on term_node_tid_idx  (cost=0.00..4.94 rows=91
width=0) (actual time=0.014..0.014 rows=0 loops=1)
     Index Cond: ((tid)::integer = 3)

That's a pretty bad estimate for a scan of a single relation with a
filter on one column.

I'd like to see the output of:

SELECT MIN(tid), MAX(tid), SUM(1) FROM term_node;
SHOW default_statistics_target;

By the way, why does EXPLAIN not display the name of the table as well
as the index when it performs a bitmap index scan?  It does do so for
a regular index scan.

What version of PG is this again?

...Robert

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Subject: Re: PostgreSQL does CAST implicitely between int and a domain derived from int
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