Re: [HACKERS] Bug#48582: psql spends hours computing results it already knows (fwd)

Then <tgl@sss.pgh.pa.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@cmu.edu for my public key.                            |
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