Re: "Triggered data change violation", once again

Stephan Szabo <sszabo(at)megazone23(dot)bigpanda(dot)com> writes:
>> I think all we need to do to implement things correctly is to consider a
>> previous event only if both xmin and cmin of the old tuple match the
>> current xact & command IDs, rather than considering it on the basis of
>> xmin alone.

> Are there any things that might update the command ID during the execution
> of the statement from inside functions that are being run?

Functions can run new commands that get new command ID numbers within
the current transaction --- but on return from the function, the current
command number is restored. I believe rows inserted by such a function
would look "in the future" to us at the outer command, and would be
ignored.

Actually, now that I think about it, the MVCC rules are that tuples with
xmin = currentxact are not visible unless they have cmin < currentcmd.
Not equal to. This seems to render the entire "triggered data change"
test moot --- I rather suspect that we cannot have such a condition
as old tuple cmin = currentcmd at all, and so we could just yank all
that code entirely.

regards, tom lane