Re: assessing parallel-safety

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Mon, Mar 16, 2015 at 2:55 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>>> Is there a reason not to make a rule that opclass members must be
>>> parallel-safe? I ask because I think it's important that the process
>>> of planning a query be categorically parallel-safe.

>> I'm not seeing the connection between those two statements. The planner
>> doesn't usually execute opclass members, at least not as such.

> Hmm, I guess I'm spouting nonsense there. The way the operator gets
> invoked during planning is that eqsel() calls it. But that doesn't
> require it to be part of an opclass; it just has to be an operator
> that's chosen that eqsel as its selectivity estimator.

Yeah. So what we'd want here is a rule that selectivity estimator
functions must be parallel-safe. For operators using estimators similar
to eqsel() that would imply a requirement on the operator's function
as well, but it's the estimator not any opclass connection that creates
that requirement.

regards, tom lane