Horton

Re: PoC/WIP: Extended statistics on expressions

Justin Pryzby <pryzby@telsasoft.com>

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From: Justin Pryzby <pryzby@telsasoft.com>
To: Tomas Vondra <tomas.vondra@enterprisedb.com>
Cc: Dean Rasheed <dean.a.rasheed@gmail.com>, pgsql-hackers@postgresql.org
Date: 2021-01-22T04:46:07Z
Lists: pgsql-hackers 
On Thu, Jan 21, 2021 at 10:01:01PM -0600, Justin Pryzby wrote:
> On Fri, Jan 22, 2021 at 04:49:51AM +0100, Tomas Vondra wrote:
> > > > | Statistics objects:
> > > > |     "public"."s2" (ndistinct, dependencies, mcv) ON  FROM t
> > 
> > Umm, for me that prints:
> 
> >     "public"."s2" ON ((i + 1)), (((i + 1) + 0)) FROM t
> > 
> > which I think is OK. But maybe there's something else to trigger the
> > problem?
> 
> Oh.  It's because I was using /usr/bin/psql and not ./src/bin/psql.
> I think it's considered ok if old client's \d commands don't work on new
> server, but it's not clear to me if it's ok if they misbehave.  It's almost
> better it made an ERROR.

I think you'll maybe have to do something better - this seems a bit too weird:

| postgres=# CREATE STATISTICS s2 ON (i+1) ,i FROM t;
| postgres=# \d t
| ...
|     "public"."s2" (ndistinct, dependencies, mcv) ON i FROM t

It suggests including additional columns in stxkeys for each expression.
Maybe that also helps give direction to response to Dean's concern?

That doesn't make old psql do anything more desirable, though.
Unless you also added attributes, all you can do is make it say things like
"columns: ctid".

> In any case, why are there so many parentheses ?

-- 
Justin

Commits

  1. Disallow extended statistics on system columns

  2. Identify simple column references in extended statistics

  3. Don't print extra parens around expressions in extended stats

  4. Change position of field "transformed" in struct CreateStatsStmt.

  5. Add transformed flag to nodes/*funcs.c for CREATE STATISTICS

  6. Stabilize stats_ext test with other collations

  7. Extended statistics on expressions

  8. Reduce duration of stats_ext regression tests

  9. Allow composite types in catalog bootstrap

  10. Convert Typ from array to list in bootstrap

  11. Disallow CREATE STATISTICS on system catalogs