Re: serializable read only deferrable

On Dec8, 2010, at 20:39 , Kevin Grittner wrote:
> The standard is tricky to read, but my reading of it is that only
> "LOCAL" changes are allowed after the transaction is underway (which
> I *think* effectively means a subtransaction), and those can't make
> the setting less strict -- you're allowed to specify the same level
> or more strict.  There would be no harm from the perspective of
> anything I'm working on to allow an in-progress transaction to be
> set to what it already has, but that seems to invite confusion and
> error more than provide a helpful feature, as far as I can tell. 
> I'm inclined not to allow it except at the start of a
> subtransaction, but don't feel strongly about it.

Hm, I think being able to assert that the isolation level really is SERIALIZABLE by simply doing "SET TRANSACTION ISOLATION LEVEL SERIALIZABLE" would be a great feature for SSI.

Say you've written a trigger which enforces some complex constraint, but is correct only for SERIALIZABLE transactions. By simply sticking a "SET TRANSACTION ISOLATION LEVEL SERIALIZABLE" at the top of the trigger you'd both document that fact it is correct only for SERIALIZABLE transactions *and* prevent corruption should the isolation level be something else due to a pilot error. Nice, simply and quite effective.

BTW, I hope to find some time this evening to review your more detailed proposal for "serializable read only deferrable"

best regards,
Florian Pflug