| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Martijn van Oosterhout <kleptog(at)svana(dot)org> |
| Cc: | Brad Nicholson <bnichols(at)ca(dot)afilias(dot)info>, pgsql-general(at)postgresql(dot)org |
| Subject: | Re: Strange Behavior with Serializable Transcations |
| Date: | 2006-06-28 20:47:49 |
| Message-ID: | 7950.1151527669@sss.pgh.pa.us |
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| Lists: | pgsql-general |
Martijn van Oosterhout <kleptog(at)svana(dot)org> writes:
> I think the issue here is that transaction begin is not when you type
> "begin" but at your first actual query. You can obviously only start a
> transaction once you know what serialisation level you want, and you
> don't see that till after the begin.
Right, the snapshot does not become set until you do a non-utility
command (normally, SELECT/INSERT/UPDATE/DELETE). This is a feature, not
a bug, because it lets the transaction take table locks before its
snapshot becomes set. I believe the Fine Manual's discussion of
concurrency includes some examples where such locks are needed ...
regards, tom lane
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