From: | Alvaro Herrera <alvherre(at)commandprompt(dot)com> |
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To: | Stuart Bishop <stuart(at)stuartbishop(dot)net> |
Cc: | Alban Hertroys <dalroi(at)solfertje(dot)student(dot)utwente(dot)nl>, pgsql-general(at)postgresql(dot)org |
Subject: | Re: attempted to lock invisible tuple - PG 8.4.1 |
Date: | 2009-10-06 19:16:55 |
Message-ID: | 20091006191655.GR5929@alvh.no-ip.org |
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Lists: | pgsql-general |
Alvaro Herrera wrote:
> I think the previous patch to snapmgr.c was mistaken. Instead of fixing
> a single trouble spot, we're better off fixing PushActiveSnapshot so
> that any use of it that involves a snapshot that's subject to a future
> command counter update should create a new copy.
For a while I was thinking this was useless, because surely
CurrentSnapshot would always be pointing to static storage, no?
However I realized that this is not the case in serializable
transactions, because such transaction need to register the current
snapshot and thus it creates a copy of it. So the problem is that in a
serializable snapshot, ActiveSnapshot may be pointing to the exact same
copy that a CommandCounterIncrement would modify.
--
Alvaro Herrera http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support
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