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: 2021-03-24T09:17:08Z
Lists: pgsql-hackers 
On Wed, Mar 24, 2021 at 09:54:22AM +0100, Tomas Vondra wrote:
> Hi Justin,
> 
> Unfortunately the query is incomplete, so I can't quite determine what
> went wrong. Can you extract the full query causing the crash, either
> from the server log or from a core file?

Oh, shoot, I didn't realize it was truncated, and I already destroyed the core
and moved on to something else...

But this fails well enough, and may be much shorter than the original :)

select distinct
     pg_catalog.variance(
       cast(pg_catalog.pg_stat_get_bgwriter_timed_checkpoints() as int8)) over (partition by subq_0.c2 order by subq_0.c0) as c0,
   subq_0.c2 as c1, subq_0.c0 as c2, subq_0.c2 as c3, subq_0.c1 as c4, subq_0.c1 as c5, subq_0.c0 as c6
 from
   (select
         ref_1.foreign_server_catalog as c0,
         ref_1.authorization_identifier as c1,
         sample_2.tgname as c2,
         ref_1.foreign_server_catalog as c3
       from
         pg_catalog.pg_stat_database_conflicts as ref_0
                 left join information_schema._pg_user_mappings as ref_1
                 on (ref_0.datname < ref_0.datname)
               inner join pg_catalog.pg_amproc as sample_0 tablesample system (5)
               on (cast(null as uuid) < cast(null as uuid))
             left join pg_catalog.pg_aggregate as sample_1 tablesample system (2.9)
             on (sample_0.amprocnum = sample_1.aggnumdirectargs )
           inner join pg_catalog.pg_trigger as sample_2 tablesample system (1) on true )subq_0;

TRAP: FailedAssertion("bms_num_members(varnos) == 1", File: "selfuncs.c", Line: 3332, PID: 16422)

Also ... with this patch CREATE STATISTIC is no longer rejecting multiple
tables, and instead does this:

postgres=# CREATE STATISTICS xt ON a FROM t JOIN t ON true;
ERROR:  schema "i" does not exist

-- 
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