Re: Documenting serializable vs snapshot isolation levels

From: "Robert Haas" <robertmhaas(at)gmail(dot)com>
To: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>
Cc: "Gregory Stark" <stark(at)enterprisedb(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Documenting serializable vs snapshot isolation levels
Date: 2008-12-30 15:58:45
Message-ID: 603c8f070812300758v1495fa17g68623e94fd6c6630@mail.gmail.com
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> The effects are different, I think, in that there isn't a
> serialization failure in some conflict cases where you would get one
> with actual updates. I found a paper on how to use updates to provide
> serializable transactions in a snapshot database, and I'd have to
> review closely to see how that difference affected the technique. I
> had been thinking that the WAL generation and bloat issues made the
> technique pretty iffy, but if SELECT FOR UPDATE suffices in place of
> most of the proposed updates, it just might be feasible.

In fact, I think SELECT FOR SHARE is enough. That will give you
better concurrency, since it will block only updates and not
concurrent read transactions.

...Robert

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