From: | Merlin Moncure <mmoncure(at)gmail(dot)com> |
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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 |
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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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