Horton

Re: Early WIP/PoC for inlining CTEs

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Andres Freund <andres@anarazel.de>
Cc: Thomas Munro <thomas.munro@enterprisedb.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: 2019-01-11T19:10:39Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  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 Fri, Jan 11, 2019 at 2:04 PM Andres Freund <andres@anarazel.de> wrote:
> > 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.
>
> I think you have some purity arguments here, but the likelihood of us
> developing a full-blown solution is not that high, and the lack of
> inlinable CTEs is *really* hurting us. As long as the design doesn't
> block a full solution, if we go there, I think it's a very acceptable
> blemish in comparison to the benefits we'd get.

Also, it seems to me that this is properly a property of the
individual WITH clause, not the query as a whole.

I mean I suppose we could do

WITH or_with_out_you OPTIONS (materialized false) AS (SELECT 'mariah
carey') SELECT ...

That'd allow for extensibility, have the write scope, and look like
what we do elsewhere.  It looks a little less elegant than

WITH cte_name [[NOT] MATERIALIZED] AS (query) main_query...

...but maybe elegance for extensibility is a good trade.

-- 
Robert Haas
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