From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
Cc: | Itagaki Takahiro <itagaki(dot)takahiro(at)gmail(dot)com>, Shigeru HANADA <hanada(at)metrosystems(dot)co(dot)jp>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: SQL/MED - core functionality |
Date: | 2010-11-25 16:18:23 |
Message-ID: | 13484.1290701903@sss.pgh.pa.us |
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Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> writes:
> I left out some details on what exactly FdwPlan should contain and what
> it's lifecycle should be. I'm thinking that it should be allocated in
> the CurrentMemoryContext that's active when the FDW Plan routine is
> called, which would be the same context where we store all the Plan
> objects. It should not be modified after creation, so that it doesn't
> need to be copied when the ForeignScan is copied with copyObject(). It
> should not contain transient state information like connection objects,
> or references to a remotely prepared cursor etc. It must be possible to
> call BeginScan multiple times with the same FdwPlan object, so that it
> can be stored in a prepared plan that is executed multiple times.
The above statements seem mutually contradictory. In particular,
I think you're proposing that copyObject copy only a pointer and not the
whole plan tree when copying ForeignScan. That is entirely
unworkable/unacceptable: quite aside from the semantic ugliness, it will
fail altogether for cached plans.
regards, tom lane
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