From: Tom Lane <tgl@sss.pgh.pa.us>
To: Florian Weimer <fweimer@bfk.de>
Cc: pgsql-sql@postgresql.org
Subject: Re: INSERT/UPDATEs cycles and lack of phantom locking
Date: Wed, 19 Jul 2006 10:26:18 -0400
Message-ID: <25634.1153319178@sss.pgh.pa.us> (raw)
In-Reply-To: <82zmf60zf4.fsf@mid.bfk.de>
References: <82zmf60zf4.fsf@mid.bfk.de>
Florian Weimer <fweimer@bfk.de> writes:
> BEGIN TRANSACTION ISOLATION LEVEL READ COMMITTED; -- SERIALIZABLE
> ...
> -- SAVEPOINT tmp_created; -- (see below)
> CREATE TEMPORARY TABLE tmp2 AS SELECT tmp.key, new_val, real.val AS old_val
> FROM tmp LEFT OUTER JOIN real ON tmp.key = real.key;
> UPDATE real SET val = new_val + old_val FROM tmp2
> WHERE old_val IS NOT NULL AND tmp2.key = real.key;
> INSERT INTO real SELECT key, new_val FROM tmp2 WHERE old_val IS NULL;
> If this is run concurrently, the INSERT may fail. In this case, I
> rerun the transaction. Actually, I want to rollback to the
> tmp_created checkpoint, but I don't think this will pick up the new
> rows in the "real" table, and the INSERT will fail again.
Why do you think that? If you're running in READ COMMITTED mode then
each statement takes a new snapshot.
regards, tom lane
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To: pgsql-sql@postgresql.org
Cc: tgl@sss.pgh.pa.us, fweimer@bfk.de
Subject: Re: INSERT/UPDATEs cycles and lack of phantom locking
In-Reply-To: <25634.1153319178@sss.pgh.pa.us>
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