Re: Compatibility GUC for serializable

"Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov> writes:
> 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 think we've learned over the years that GUCs that significantly change
semantics can be foot-guns. I'm not sure exactly how dangerous this one
would be, but on the whole I'd prefer to avoid introducing a GUC here.

regards, tom lane