| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | "Craig A(dot) James" <cjames(at)modgraph-usa(dot)com> |
| Cc: | Steve Atkins <steve(at)blighty(dot)com>, pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: Performance of count(*) |
| Date: | 2007-03-22 18:37:26 |
| Message-ID: | 20588.1174588646@sss.pgh.pa.us |
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| Lists: | pgsql-performance |
"Craig A. James" <cjames(at)modgraph-usa(dot)com> writes:
> Steve Atkins wrote:
>> As long as you're ordering by some row in the table then you can do that in
>> straight SQL.
>>
>> select a, b, ts from foo where (stuff) and foo > X order by foo limit 10
>>
>> Then, record the last value of foo you read, and plug it in as X the next
>> time around.
> We've been over this before in this forum: It doesn't work as advertised. Look for postings by me regarding the fact that there is no way to tell the optimizer the cost of executing a function. There's one, for example, on Oct 18, 2006.
You mean
http://archives.postgresql.org/pgsql-performance/2006-10/msg00283.php
? I don't see anything there that bears on Steve's suggestion.
(The complaint is obsolete as of CVS HEAD anyway.)
regards, tom lane
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