Re: Early WIP/PoC for inlining CTEs

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk>
Cc: Andreas Karlsson <andreas(at)proxel(dot)se>, David Fetter <david(at)fetter(dot)org>, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Early WIP/PoC for inlining CTEs
Date: 2019-01-27 15:21:55
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Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk> writes:
> I'm not sure we should nail down the rule that the absence of NOT
> MATERIALIZED will mean a multiply-referenced CTE is evaluated once. One
> would hope that in the future the planner might be taught to inline or
> not in that case depending on cost. I think it makes more sense to say
> that we never inline if MATERIALIZED is specified, that we always inline
> if NOT MATERIALIZED is specified, and that if neither is specified the
> planner will choose (but perhaps note that currently it always chooses
> only based on refcount).

I have no objection to documenting it like that; I just don't want us
to go off into the weeds trying to actually implement something smarter
for v12.

regards, tom lane

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