Re: User-facing aspects of serializable transactions

Peter Eisentraut wrote:
> 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?

I don't think you need that for predicate locking. To determine if e.g 
an INSERT and a SELECT conflict, you need to determine if the INSERTed 
tuple matches the predicate in the SELECT. No need to deduce anything 
between two predicates, but between a tuple and a predicate.

--   Heikki Linnakangas  EnterpriseDB   http://www.enterprisedb.com