Re: *_collapse_limit, geqo_threshold

From: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>
To: "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: "Robert Haas" <robertmhaas(at)gmail(dot)com>, "Dimitri Fontaine" <dim(at)hi-media(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: *_collapse_limit, geqo_threshold
Date: 2009-07-10 17:59:48
Message-ID: 4A573B4402000025000286A7@gw.wicourts.gov
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Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov> writes:
>> treat parentheses around JOIN operations as optimizer hints.
>
> That's a *truly* horrid idea, as sometimes you need them simply to
> get the precedence correct.

You do, but it's been pretty rare in my experience, and we're
considering alternatives which give a lot less flexibility that this.

The *truly* awful thing about the SAP-DB implementation is that it
wasn't optional -- parentheses in this part of a query always limited
optimizer options; I sure wouldn't want to go there again. I thought
we were talking about options for what to do when an enable_* setting
was off for diagnostic purposes....

-Kevin

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