Horton

Re: pg_stat_statements and "IN" conditions

Dmitry Dolgov <9erthalion6@gmail.com>

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From: Dmitry Dolgov <9erthalion6@gmail.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Zhihong Yu <zyu@yugabyte.com>, David Steele <david@pgmasters.net>, PostgreSQL-development <pgsql-hackers@postgresql.org>, Greg Stark <stark@mit.edu>, Pavel Trukhanov <pavel.trukhanov@gmail.com>
Date: 2022-03-14T15:10:28Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Introduce squashing of constant lists in query jumbling

  2. Make documentation builds reproducible

  3. Include values of A_Const nodes in query jumbling

  4. Teach planner about more monotonic window functions

  5. Split up guc.c for better build speed and ease of maintenance.

> On Mon, Mar 14, 2022 at 11:02:16AM -0400, Robert Haas wrote:
> On Mon, Mar 14, 2022 at 10:57 AM Dmitry Dolgov <9erthalion6@gmail.com> wrote:
> > Well, yeah, the commit message is somewhat clumsy in this regard. It
> > works almost in the way you've described, except if the list is all
> > constants and long enough to satisfy the threshold then *first N
> > elements (where N == threshold) will be jumbled -- to leave at least
> > some traces of it in pgss.
>
> But that seems to me to be a thing we would not want. Why do you think
> otherwise?

Hm. Well, if the whole list would be not jumbled, the transformation
would look like this, right?

WHERE x in (1, 2, 3, 4, 5) -> WHERE x in (...)

Leaving some number of original elements in place gives some clue for
the reader about at least what type of data the array has contained.
Which hopefully makes it a bit easier to identify even in the collapsed
form:

WHERE x in (1, 2, 3, 4, 5) -> WHERE x in (1, 2, ...)

> > I'm not sure if I follow the last point. WHERE x in (1,3) and x =
> > any(array[1,3]) are two different things for sure, but in which way are
> > they going to be mixed together because of this change? My goal was to
> > make only the following transformation, without leaving any uncertainty:
> >
> > WHERE x in (1, 2, 3, 4, 5) -> WHERE x in (1, 2, ...)
> > WHERE x = any(array[1, 2, 3, 4, 5]) -> WHERE x = any(array[1, 2, ...])
>
> I understand. I think it might be OK to transform both of those
> things, but I don't think it's very clear either from the comments or
> the nonexistent documentation that both of those cases are affected --
> and I think that needs to be clear. Not sure exactly how to do that,
> just saying that we can't add behavior unless it will be clear to
> users what the behavior is.

Yep, got it.