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Re: AW: AW: AW: AW: relation ### modified while in use

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Zeugswetter Andreas SB <ZeugswetterA(at)wien(dot)spardat(dot)at>
Cc: "'Hiroshi Inoue'" <Inoue(at)tpf(dot)co(dot)jp>, pgsql-hackers(at)postgreSQL(dot)org
Subject: Re: AW: AW: AW: AW: relation ### modified while in use
Date: 2000-10-23 15:44:44
Message-ID: 8773.972315884@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Zeugswetter Andreas SB <ZeugswetterA(at)wien(dot)spardat(dot)at> writes:
> Yes, and holding a row exclusive lock must imho at least grab a shared
> table lock

As indeed it does.  Our disagreement seems to be just on the point of
whether it's safe to allow a read-only transaction to release its 
AccessShareLock locks partway through.

My opinion about that is colored by the known bugs that we have because
the parser/rewriter/planner currently do just that.  You can cause the
system to become mighty confused if the report of a table schema change
arrives partway through the parse/plan process, because decisions
already made are no longer valid.  While we can probably patch the holes
in this area by holding a lock throughout processing of one statement,
I think that will just push the problem up to the application level.
How many apps are likely to be coded in a way that will be robust
against intra-transaction schema changes?

			regards, tom lane

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