Horton

Re: PoC/WIP: Extended statistics on expressions

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Tomas Vondra <tomas.vondra@enterprisedb.com>
Cc: Noah Misch <noah@leadboat.com>, Dean Rasheed <dean.a.rasheed@gmail.com>, Justin Pryzby <pryzby@telsasoft.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2021-06-06T20:08:52Z
Lists: pgsql-hackers 
Tomas Vondra <tomas.vondra@enterprisedb.com> writes:
> On 6/6/21 9:17 PM, Tom Lane wrote:
>> I'm curious about how come the buildfarm didn't notice this.  The
>> animals using COPY_PARSE_PLAN_TREES should have failed.  The fact
>> that they didn't implies that there's no test case that makes use
>> of a nonzero value for this field, which seems like a testing gap.

> AFAICS the reason is pretty simple - the COPY_PARSE_PLAN_TREES checks
> look like this:
> ...
> But if the field is missing from all the functions, equal() can't detect
> that copyObject() did not actually copy it.

Right, that code would only detect a missing copyfuncs.c line if
equalfuncs.c did have the line, which isn't all that likely.  However,
we then pass the copied node on to further processing, which in principle
should result in visible failures when copyfuncs.c is missing a line.

I think the reason it didn't is that the transformed field would always
be zero (false) in grammar output.  We could only detect a problem if
we copied already-transformed nodes and then used them further.  Even
then it *might* not fail, because the consequence would likely be an
extra round of parse analysis on the expressions, which is likely to
be a no-op.

Not sure if there's a good way to improve that.  I hope sometime soon
we'll be able to auto-generate these functions, and then the risk of
this sort of mistake will go away (he says optimistically).

			regards, tom lane

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