From: | "Jeff Larsen" <jlar310(at)gmail(dot)com> |
---|---|
To: | pgsql-performance(at)postgresql(dot)org |
Subject: | Re: Union within View vs.Union of Views |
Date: | 2007-11-04 01:57:21 |
Message-ID: | d1f9b6f00711031857s2972e92dgcedb209233f2485a@mail.gmail.com |
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Lists: | pgsql-performance |
[[ Oops, still not used to gmail. Accidentally posted this straight to
Tom and not the list]]
> There are a bunch of special cases where it can't do that, though.
> Look into src/backend/optimizer/path/allpaths.c, particularly
> subquery_is_pushdown_safe:
My case probably fits the 'special case' description. Not all the
columns in each subquery matched up, so there were NULL::text
placeholders in some spots in the SELECT. In the case where
performance got bad, one of those columns was included in the
application's WHERE clause.
That's a good enough explanation for me. I'll spare you the gory
details of my tables, unless a developer wants to have a look at it
off-list.
Jeff
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