Re: User-facing aspects of serializable transactions

--  
Greg


On 28 May 2009, at 02:49, Tom Lane <tgl@sss.pgh.pa.us> wrote:

> Greg Stark <greg.stark@enterprisedb.com> writes:
>> Without any real way to represent predicates this is all pie in the
>> sky. The reason we don't have predicate locking is because of this
>> problem which it sounds like we're no closer to solving.
>
> 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.
>

I think you get "true serializability" in the sense that you take out  
a full table lock on every read. I.e. Your transactions end up  
actually serialized... Well it would be a bit weaker than that due to  
the weak read-locks but basically you would get random spurious  
serialization failures which can't be explained by inspecting the  
transactions without understanding the implementation.