Re: Documenting serializable vs snapshot isolation levels

On Mon, 2008-12-29 at 18:13 -0600, Kevin Grittner wrote:

> I hope someone can show me something good I've missed so far.

You're viewing this in problem-exposed language, unintentionally I'm
sure. My viewpoint on this is that database concurrency is a big issue,
but that the way we do things round here is a major leap forward on the
way things happened previously (and still do in older-style DBMS).

Our approach to serializable queries is an optimistic one in two ways:
It covers most cases, but not all theoretical cases. It also avoids
locks by default. 

Those are good things, with many benefits. If we put the default the
other way around, developers would spend much more time re-tuning
queries that had locked each other out. So I would say we choose to
avoid locking-on-every-query with good reason. Just look at the
facilities DB2 provides to avoid it. Ugh-ly.

-- Simon Riggs           www.2ndQuadrant.comPostgreSQL Training, Services and Support