Horton

Re: Early WIP/PoC for inlining CTEs

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andreas Karlsson <andreas@proxel.se>
Cc: Robert Haas <robertmhaas@gmail.com>, Andres Freund <andres@anarazel.de>, Thomas Munro <thomas.munro@enterprisedb.com>, Andrew Gierth <andrew@tao11.riddles.org.uk>, David Fetter <david@fetter.org>, Pg Hackers <pgsql-hackers@postgresql.org>
Date: 2019-01-17T15:52:19Z
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

Andreas Karlsson <andreas@proxel.se> writes:
> On 1/11/19 8:10 PM, Robert Haas wrote:
>> WITH cte_name [[NOT] MATERIALIZED] AS (query) main_query...

> Hm, when would one want "NOT MATERIALIZED"? I am not sure I see the 
> usefulness of forcing inlining other than if we by default do not inline 
> when a CTE is referenced multiple times.

I'm also concerned about what we do if the user says NOT MATERIALIZED
but there are semantic or implementation reasons not to inline.  Either
we throw an error or do something the user didn't expect, and neither
is very nice.  So I'm not in favor of having that option.

			regards, tom lane