Re: bug with dropping tables and transactions.

* Hiroshi Inoue <Inoue(at)tpf(dot)co(dot)jp> [000912 00:45] wrote:
> > -----Original Message-----
> > From: Alfred Perlstein
> >
> > There seems to a race condition somewhere where that if you're
> > running let's say pg_dumpall and happen to drop a table mid-dump
> > pg_dumpall will die because it looses the table.
> >
> > Would it make sense to use a transaction system so that when a table
> > is renamed/dropped it doesn't actually go away until all transactions
> > that started before the drop take place?
> >
> > one could do probably implement this using refcounts and translating
> > dropped tables into temporary mangled names.
> >
>
> Your proposal seems to be an extension of how to commit/rollback
> DDL (drop/alter/rename etc ..) commands properly. There has been
> a long discussion about it but unfortunately we have no consensus
> for it AFAIK.
>
> There may be another way.
> pg_dump(all) may be able to acquire a e.g share lock for pg_class
> to prevent drop/rename/.. operations of other backends. Of cource
> DDL(drop/rename/..) commands should acquire a row exclusive
> lock on pg_class.

No long term locks is better than a locking system, I'd prefer to
be able to proceed as normal since a transaction exists 'at a point
in time' there's no reason to delay a drop that happens in the
future so long as there's still something for the old transaction
to grab onto.

Your solution may be simpler (and I thought of something like it
already) but honestly it's not what I'd like to see implemented.

--
-Alfred Perlstein - [bright(at)wintelcom(dot)net|alfred(at)freebsd(dot)org]
"I have the heart of a child; I keep it in a jar on my desk."