Re: is necessary to recheck cached data in fn_extra?

Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> writes:
> st 7. 8. 2019 v 17:39 odesílatel Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> napsal:
>> I wouldn't trust that. You don't really know what the lifespan of
>> a fn_extra cache is.

> fn_extra cache cannot be longer than query.

There are fn_extra caches that are not tied to queries. Admittedly
they're for special purposes like I/O functions and index support
functions, and maybe you can assume that your function can't be
used in such ways. I don't think it's a great programming model
though.

> And if I understand well, then
> is not possible to change parameter types inside query?

Most places dealing with composite types assume that the rowtype *could*
change intraquery. I believe this was a live possibility in the past,
though it might not be today. (The issue was inheritance queries, but
I think we now force tuples from child tables to be converted to the
parent rowtype. Whether that's 100% bulletproof is unclear.) If you're
not dealing with composites then it's an okay assumption. I think.

regards, tom lane