Horton

Re: Early WIP/PoC for inlining CTEs

Gavin Flower <gavinflower@archidevsys.co.nz>

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From: Gavin Flower <GavinFlower@archidevsys.co.nz>
To: Andres Freund <andres@anarazel.de>, Jeremy Finzel <finzelj@gmail.com>
Cc: Andrew Gierth <andrew@tao11.riddles.org.uk>, pgsql-hackers@postgresql.org
Date: 2018-07-24T23:50:12Z
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 25/07/18 11:10, Andres Freund wrote:
> On 2018-07-24 18:03:43 -0500, Jeremy Finzel wrote:
>> On Tue, Jul 24, 2018 at 5:28 PM Andrew Gierth <andrew@tao11.riddles.org.uk>
>> wrote:
>>
[...]
>>> In our environment we often want this to be a fence.  For example it can
[...]
> This essentially has been discussed already:
> http://archives.postgresql.org/message-id/5351711493487900%40web53g.yandex.ru
>
> My read of the concensus (in which I am in the majority, so I might be
> biased) is that we do want inlining to be the default. We were thinking
> that it'd be necessary to provide a way to force inlining on the SQL
> level for individual CTEs.
>
>
>> Curious what other RDBMSs do here?
> They largely inline by default.
>
> Greetings,
>
> Andres Freund
>
If I'd not read anything about CTE's being a fence, I would have 
implicitly assumed that they were optimised together with the main part 
of the SQL statement, and I suspect that is the case for most people.

So I'm very much a favour of optimisation of CTE's being the default.


Cheers,
Gavin