On Thursday 28 May 2009 04:49:19 Tom Lane wrote:
> Yeah. The fundamental problem with all the "practical" approaches I've
> heard of is that they only work for a subset of possible predicates
> (possible WHERE clauses). The idea that you get true serializability
> only if your queries are phrased just so is ... icky. So icky that
> it doesn't sound like an improvement over what we have.
Is it even possible to have a predicate locking implementation that can verify
whether an arbitrary predicate implies another arbitrary predicate? And this
isn't constraint exclusion, where it is acceptable to have false negatives.