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RE: relation ### modified while in use

From: "Hiroshi Inoue" <Inoue(at)tpf(dot)co(dot)jp>
To: "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: <pgsql-hackers(at)postgresql(dot)org>
Subject: RE: relation ### modified while in use
Date: 2000-11-02 21:49:35
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Lists: pgsql-hackers
> -----Original Message-----
> From: Tom Lane [mailto:tgl(at)sss(dot)pgh(dot)pa(dot)us]
> Hiroshi Inoue <Inoue(at)tpf(dot)co(dot)jp> writes:
> > Do we have a conclusion about this thread ?
> > If no,how about changing heap_open(r) so that they allocate
> > Relation descriptors after acquiring a lock on the table ?
> > We would use LockRelation() no longer.
> That won't do by itself,

Doesn't current heap_open() have a flaw that even the first 
use of a relation in a transaction may cause an error
"relation ### modified while in use" ?

> because that will open us up to failures when
> a relcache invalidation arrives mid-transaction and we don't happen to
> have the relation open at the time.  We could still have parse/plan
> results that depend on the old relation definition.

PL/pgSQL already prepares a plan at the first execution
time and executes the plan repeatedly after that.
We would have general PREPARE/EXECUTE feature in the
near fututre. IMHO another mechanism to detect plan invali
dation is needed.

BTW,I sometimes see 
    ERROR:  SearchSysCache: recursive use of cache 10(16)
under small MAXNUMMESSAGES environment.
I'm not sure about the cause but suspicious if sufficiently
many system relations are nailed for "cache state reset".

Hiroshi Inoue

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