| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Marko Tiikkaja <marko(dot)tiikkaja(at)cs(dot)helsinki(dot)fi> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Hitoshi Harada <umi(dot)tanuki(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: How to share the result data of separated plan |
| Date: | 2010-11-08 18:30:58 |
| Message-ID: | 27265.1289241058@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Marko Tiikkaja <marko(dot)tiikkaja(at)cs(dot)helsinki(dot)fi> writes:
> On 2010-11-08 7:26 PM +0200, Tom Lane wrote:
>> The alternative is to artificially serialize the DML CTEs, which
>> while it does have some advantages doesn't seem like a win overall.
> We've discussed this before and the consensus was that as long as we
> don't change the results, we can optimize the materialization away.
No, because the problem is mainly about what might happen if
user-defined functions choose to look at the target tables. We can't
really tell what triggers are going to do, to take one item that the
planner has no access to.
I think we have to decide up front which implementation behavior
it's going to be, and if we go with serialized queries, we'll be
stuck with that.
regards, tom lane
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