From: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
---|---|
To: | Martin Neumann <mne(at)mne(dot)de> |
Cc: | pgsql-bugs(at)postgresql(dot)org |
Subject: | Re: Number of tuples in pg_class - bug or misunderstanding? |
Date: | 2000-05-11 15:12:59 |
Message-ID: | 200005111512.LAA11713@candle.pha.pa.us |
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Lists: | pgsql-bugs |
> I'm just digging a little bit in PostgreSQL internals and I found the
> following thing. Shouldn't the reltuples field in pg_class contain the
> real number of tuples? It is always a little bit to low ...
>
> irc=# SELECT reltuples FROM pg_class WHERE relname = 'events';
> reltuples
> -----------
> 188
> (1 row)
>
> irc=# SELECT COUNT(*) FROM events;
> count
> -------
> 195
> (1 row)
>
>
> This annoys me a little bit as I can do
> SELECT reltuples FROM pg_class WHERE relname = $1;
> from plpgsql, but not
> SELECT COUNT(*) FROM $1;
reltuples is updated only by VACUUM. The performance hit is too great
to keep it up-to-date, we think, though if it was accurate, we could
optimize COUNT(*) with no WHERE.
--
Bruce Momjian | http://www.op.net/~candle
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
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