Re: Compatibility GUC for serializable

On Sun, Jan 09, 2011 at 12:07:49PM -0600, Kevin Grittner wrote:
> There's an issue where we don't seem to have consensus yet, so I
> figured I'd bounce it off the list.
>
> If the SSI patch were to be accepted as is, REPEATABLE READ would
> continue to provide the exact same snapshot isolation behavior which
> both it and SERIALIZABLE do through 9.0, and SERIALIZABLE would
> always use SSI on top of the snapshot isolation to prevent
> serialization anomalies. In his review, Jeff argued for a
> compatibility GUC which could be changed to provide legacy behavior
> for SERIALIZABLE transactions -- if set, SERIALIZABLE would fall
> back to working the same as REPEATABLE READ.
>
> In an off-list exchange with me, David Fetter expressed opposition
> to this, as a foot-gun. I'm not sure where anyone else stands on
> this. Personally, I don't care a whole lot because it's trivial to
> add, so that seems to leave the vote at 1 to 1. Anyone else care to
> tip the scales?

For what it's worth, that exchange started with my proposing a
separate SNAPSHOT isolation, but since we'll already providing that
isolation level and calling it REPEATABLE READ, I figured we didn't
need an extra one that did the exact same thing. :)

Cheers,
David.
--
David Fetter <david(at)fetter(dot)org> http://fetter.org/
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