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Re: User-facing aspects of serializable transactions

From: Greg Stark <greg(dot)stark(at)enterprisedb(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, Jeff Davis <pgsql(at)j-davis(dot)com>, "<pgsql-hackers(at)postgresql(dot)org>" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: User-facing aspects of serializable transactions
Date: 2009-05-28 01:57:20
Message-ID: A46E65F6-FAE0-474E-B5C6-185689312F09@enterprisedb.com (view raw or flat)
Thread:
Lists: pgsql-hackers

--  
Greg


On 28 May 2009, at 02:49, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Greg Stark <greg(dot)stark(at)enterprisedb(dot)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. 
  

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