From: | Marko Tiikkaja <marko(dot)tiikkaja(at)cs(dot)helsinki(dot)fi> |
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To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
Cc: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Writeable CTEs and side effects |
Date: | 2009-10-08 11:02:41 |
Message-ID: | 4ACDC6D1.7000703@cs.helsinki.fi |
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Lists: | pgsql-hackers |
Robert Haas wrote:
> This has one MAJOR disadvantage: all the tuples from the CTE queries
> have to be buffered someplace, rather than streamed from the subquery
> up to the main query. For what may turn out to be pretty common uses
> cases like WITH tuples AS (DELETE FROM big_table_1 RETURNING ...)
> INSERT INTO big_table_2 ... this is going to suck pretty bad. I
> wonder if it isn't better to just use the same command-ID throughout
> and live with the weirdness of #2.
I haven't looked at the CTE code in much detail but I was under the
impression that it had to store the results somewhere in any case.
You're right, though, it sucks for this use case. Weirdness of #2 is
probably a lot easier to live with.
> I think you should definitely get some input from Tom Lane on this
> before you go too much further, but if he doesn't respond to this
> thread, I suggest trying again after CommitFest.
Agreed.
> Does this have any impact on the pending DML-node patch?
Not really. This could be done without the patch, but we can use far
more of the existing CTE code with the patch.
Regards,
Marko Tiikkaja
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