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Re: CTE optimization fence on the todo list?

From: Merlin Moncure <mmoncure(at)gmail(dot)com>
To: Daniel Browning <db(at)kavod(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: CTE optimization fence on the todo list?
Date: 2012-10-01 13:05:18
Message-ID: CAHyXU0zpM5+Dsb_pKxDmm-ZoWUAt=SkHHaiK_DBqcmtxTas6Nw@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Wed, Sep 19, 2012 at 3:05 PM, Daniel Browning <db(at)kavod(dot)com> wrote:
> Another good reason to reject it might be because the only way to disable
> the CTE fence is to disable it by default. If that were the case, then I
> would imagine that it would break backwards compatibility, especially in the
> case of writable CTEs that currently depend on the fence for their current
> functionality.

Yeah: I constantly rely on CTE fencing and it's a frequently suggested
performance trick on the lists.  LATERAL is coming out soon and this
will remove one of the largest reasons to fence but there are of
course others. Also, a GUC setting is almost certainly the wrong
approach.

I'm wondering if there are any technical/standards constraints that
are behind the fencing behavior.  If there aren't any, maybe an opt-in
keyword might do the trick -- WITH UNBOXED foo AS (..)?

merlin


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Subject: Re: CTE optimization fence on the todo list?
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