From: | Brian E Gallew <geek+(at)cmu(dot)edu> |
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To: | pgsql-hackers(at)postgreSQL(dot)org |
Subject: | Re: [HACKERS] Bug#48582: psql spends hours computing results it already knows (fwd) |
Date: | 1999-10-29 02:44:12 |
Message-ID: | emacs-smtp-1573-14361-2556-312146@export.andrew.cmu.edu |
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Lists: | pgsql-hackers |
Then <tgl(at)sss(dot)pgh(dot)pa(dot)us> spoke up and said:
> The short answer to this is that maintaining a perfectly accurate tuple
> count on-the-fly would almost certainly cost more, totalled over all
> operations that modify a table, than we could ever hope to make back
> by short-circuiting "select count(*)" operations. (Consider
> concurrent transactions running in multiple backends, some of which
> may abort instead of committing, and others of which may already have
> committed but your transaction is not supposed to be able to see their
> effects...)
So, does the planner allow counting from a unique index (if one
exists)? In general, an index scan on a unique index should be faster
than a table scan. Of course, I'm sure someone already thought of this...
--
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| JAVA must have been developed in the wilds of West Virginia. |
| After all, why else would it support only single inheritance?? |
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| Finger geek(at)cmu(dot)edu for my public key. |
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Next Message | Tom Lane | 1999-10-29 03:57:59 | Re: [HACKERS] Bug#48582: psql spends hours computing results it already knows (fwd) |
Previous Message | The Hermit Hacker | 1999-10-29 01:45:37 | Re: 6.5.3 |