| From: | Mladen Gogala <mladen(dot)gogala(at)vmsinfo(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Jeremy Palmer <JPalmer(at)linz(dot)govt(dot)nz>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: Possible to improve query plan? |
| Date: | 2011-01-17 22:11:09 |
| Message-ID: | 4D34BE7D.3070007@vmsinfo.com |
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| Lists: | pgsql-performance |
Tom Lane wrote:
> If I'm not mistaken, that's a DB2-ish locution
It could also be a part of the Oracle vernacular. I've seen queries like
that running against Oracle RDBMS, too.
> for a query with DISTINCT
> ON, ie, you're looking for the row with highest _revision_created for
> each value of id. It might perform well on DB2, but it's going to
> mostly suck on Postgres --- we don't optimize window-function queries
> very much at all at the moment.
Hmmm, what optimizations do you have in mind? I thought that window
functions are just clever tricks with memory? Anything that can be
expected for 9.0x?
> Try writing it with DISTINCT ON instead
> of a window function, like so:
>
Wouldn't "distinct" necessarily bring about the sort/merge?
--
Mladen Gogala
Sr. Oracle DBA
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New York, NY 10036
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