Re: pg_stat_statements and "IN" conditions

> On Thu, Mar 10, 2022 at 12:32:08PM -0500, Robert Haas wrote:
> On Thu, Mar 10, 2022 at 12:12 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> > 2. You haven't made a case for it. The original complaint was
> > about different lengths of IN lists not being treated as equivalent,
> > but this patch has decided to do I'm-not-even-sure-quite-what
> > about treating different Params as equivalent. Plus you're trying
> > to invoke eval_const_expressions in the jumbler; that is absolutely
> > Not OK, for both safety and semantic reasons.
>
> I think there are two separate points here, one about patch quality
> and the other about whether the basic idea is good. I think the basic
> idea is good. I do not contend that collapsing IN-lists of arbitrary
> length is what everyone wants in all cases, but it seems entirely
> reasonable to me to think that it is what some people want. So I would
> say just make it a parameter and let people configure whichever
> behavior they want. My bet is 95% of users would prefer to have it on,
> but even if that's wildly wrong, having it as an optional behavior
> hurts nobody. Let it be off by default and let those who want it flip
> the toggle. On the code quality issue, I haven't read the patch but
> your concerns sound well-founded to me from reading what you wrote.

I have the same understanding, there is a toggle in the patch exactly
for this purpose.

To give a bit more context, the whole development was ORM-driven rather
than pulled out of thin air -- people were complaining about huge
generated queries that could be barely displayed in monitoring, I was
trying to address it via collapsing the list where it was happening. In
other words "I'm-not-even-sure-quite-what" part may be indeed too
extensive, but was triggered by real world issues.

Of course, I could get the implementation not quite right, e.g. I wasn't
aware about dangers of using eval_const_expressions. But that's what the
CF item and the corresponding discussion is for, I guess. Let me see
what I could do to improve it.