Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Hmm, what I gathered was that that's not changing any basic semantic
> guarantees (and therefore is okay to control as a GUC). But I
> haven't read the paper so maybe I'm missing something.
The paper never suggests attempting these techniques without a
predicate locking implementation. It was just something Robert Haas
noticed during our discussion at the bar (and he wasn't even consuming
any alcohol that night!) that it would be a possible development path.
I don't think either of us sees it as a useful end point.
Basically, if you just took out locks on the rows you happened to read
(rather than doing proper predicate locking) you would still prevent
some anomalies, in a more-or-less predictable and controllable way. I
think we both felt that the predicate locking might be the hardest
part to implement in PostgreSQL, so having such a proof of concept
partial implemenation without first implementing predicate locking
might fit with the "series of smaller patches" approach generally
preferred by the PostgreSQL developers.
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