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: Andreas Karlsson <andreas@proxel.se>
Cc: 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: 2019-01-10T02:24:19Z
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

On Thu, Jan 10, 2019 at 2:28 PM Andreas Karlsson <andreas@proxel.se> wrote:
> 2. Feedback on the new syntax. I am personally fine with the current
> syntax, but it was just something I just quickly hacked together to move
> the patch forward and which also solved my personal uses cases.

Thanks for working on this.  I very much want to see this feature go
in.  As mentioned by Andres up-thread, TPC-DS makes a lot of use of
CTEs... let me see, 34 queries out of 99 have a WITH clause.  These
will hopefully become candidates for parallel query.

I know this is a thorny topic, but I have to say that I am uneasy
about the MATERIALIZED syntax.  Here's how you write that in some
other RDBMS that loves hints:

WITH foo AS (SELECT /*+ MATERIALIZE */ ...)

I understood that it was a long standing project policy that we don't
want planner hints, but now we have a proposal to support one with a
top-level non-standard syntax.  If we take this syntax, should we not
also accept MATERIALIZED in front of subselects?

-1

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