Re: slow queries, possibly disk io - Mailing list pgsql-performance

From Josh Close
Subject Re: slow queries, possibly disk io
Date
Msg-id 4a0cafe205052707541373ab8a@mail.gmail.com
Whole thread Raw
In response to Re: slow queries, possibly disk io  (Tom Lane <tgl@sss.pgh.pa.us>)
List pgsql-performance
> I think you really want that seqscan to be an indexscan, instead.
> I'm betting this is PG 7.4.something?  If so, probably the only
> way to make it happen is to simplify the now() expression to a constant:
>
>             SELECT COALESCE( SUM( iNumSent ), 0 ) AS iNumSent
>             FROM adaption.tblBatchHistory_\' || this_rServerIds.iId || \'
>             WHERE tStamp > \\\'' || (now() - interval \'5 mins\')::text ||
>             \'\\\'\';

The dollar sign thing would be a lot easier. I can't get this to work.
I'm using a db manager where I can just use ' instead of \'. How would
it look for that? In other words, it doesn't have the "create or
replace function as ' --stuff ' language 'plpgsql'" it just has the
actual function. Makes things a little easier. I'm getting an error at
or near "5".

>
> because pre-8.0 the planner won't realize that the inequality is
> selective enough to favor an indexscan, unless it's comparing to
> a simple constant.
>
> (BTW, 8.0's dollar quoting makes this sort of thing a lot less painful)
>
>                         regards, tom lane
>


--
-Josh

pgsql-performance by date:

Previous
From: Tom Lane
Date:
Subject: Re: slow queries, possibly disk io
Next
From: Josh Close
Date:
Subject: Re: slow queries, possibly disk io