Re: Early WIP/PoC for inlining CTEs

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Michael Paquier <michael(at)paquier(dot)xyz>
Cc: Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Andreas Karlsson <andreas(at)proxel(dot)se>, Andres Freund <andres(at)anarazel(dot)de>, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk>, David Fetter <david(at)fetter(dot)org>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Early WIP/PoC for inlining CTEs
Date: 2019-02-02 19:01:01
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I wrote:
> I propose that we implement and document this as
> WITH ctename AS [ MATERIALIZE { ON | OFF } ] ( query )
> which is maybe a bit clunky but not awful, and it would leave room
> to generalize it to "AS [ optionname optionvalue [ , ... ] ]" if we
> ever need to. Looking at the precedent of e.g. EXPLAIN, we could
> probably allow just "MATERIALIZE" as well, with the boolean value
> defaulting to true.

In hopes of moving things along, here's a version of the patch that
does it like that. This demonstrates that, in fact, we can accept
"keyword [value] [, ...]" style options without any parens and
there's no syntax conflict. We'd have to work a bit harder on the
actual code in gram.y if we wanted to handle multiple options,
but the Bison productions will work.

There's nothing particularly stopping us from accepting
"materialized" with a D in this syntax, instead of or in addition
to "materialize"; though I hesitate to mention it for fear of
another round of bikeshedding.

After further reflection I really don't like Andrew's suggestion
that we not document the rule that multiply-referenced CTEs won't
be inlined by default. That would be giving up the principle
that WITH calculations are not done multiple times by default,
and I draw the line at that. It's an often-useful behavior as
well as one that's been documented from day one, so I do not accept
the argument that we might someday override it on the basis of
nothing but planner cost estimates.

regards, tom lane

Attachment Content-Type Size
inlining-ctes-v11.patch text/x-diff 41.9 KB

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