Horton

Re: Early WIP/PoC for inlining CTEs

Thomas Munro <thomas.munro@enterprisedb.com>

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From: Thomas Munro <thomas.munro@enterprisedb.com>
To: Andres Freund <andres@anarazel.de>
Cc: Robert Haas <robertmhaas@gmail.com>, Andreas Karlsson <andreas@proxel.se>, Andrew Gierth <andrew@tao11.riddles.org.uk>, Tom Lane <tgl@sss.pgh.pa.us>, David Fetter <david@fetter.org>, Pg Hackers <pgsql-hackers@postgresql.org>
Date: 2019-01-11T18:58:39Z
Lists: pgsql-hackers

Commits

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  1. Prevent inlining of multiply-referenced CTEs with outer recursive refs.

  2. Allow user control of CTE materialization, and change the default behavior.

  3. Split QTW_EXAMINE_RTES flag into QTW_EXAMINE_RTES_BEFORE/_AFTER.

  4. document when PREPARE uses generic plans

On Sat, Jan 12, 2019 at 7:19 AM Andres Freund <andres@anarazel.de> wrote:
> On 2019-01-11 11:12:25 -0500, Robert Haas wrote:
> > I actually think that we should go "all in" here and allow the user to
> > specify either that they want materialization or that they don't want
> > materialization.  If they specify neither, then we make some decision
> > which we may change in a future release.  If they do specify
> > something, we do that.
>
> +many

I think the syntax as proposed is almost OK if we only want to
grandfather in our historically hintful CTEs but discourage the
development of any future kinds of hints.  Even then I don't love the
way it formalises a semi-procedural step at the same language level as
a glorious declarative relational query.

Maybe we could consider a more extensible syntax that is attached to
the contained SELECT rather than the containing WITH.  Then CTEs would
be less special; there'd be a place to put hints controlling top-level
queries, subselects, views etc too (perhaps eventually join hints,
parallelism hints etc, but "materialize this" would be just another
one of those things).  That'd be all-in.

-- 
Thomas Munro
http://www.enterprisedb.com