Re: serializable read only deferrable

"Kevin Grittner" <Kevin.Grittner@wicourts.gov> writes:
> Oh, I just went through the code on setting READ ONLY and discovered
> that contrary to the standard *and* the PostgreSQL documentation,
> you can change the status of a transaction between READ ONLY and
> READ WRITE at will.  Yeah, that's a problem for my intended use.
> Many optimizations would need to go right out the window, and the
> false positive rate under SSI would be high.

I believe you had better support the locution
begin;set transaction read only;...

I agree that letting it be changed back to read/write after that is
surprising and unnecessary.  Perhaps locking down the setting at the
time of first grabbing a snapshot would be appropriate.  IIRC that's
how it works for transaction isolation level, and this seems like it
ought to work the same.
        regards, tom lane