Horton

Missing update of all_hasnulls in BRIN opclasses

Tomas Vondra <tomas.vondra@enterprisedb.com>

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From: Tomas Vondra <tomas.vondra@enterprisedb.com>
To: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2022-10-21T15:23:45Z
Lists: pgsql-hackers

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Hi,

While working on some BRIN code, I discovered a bug in handling NULL
values - when inserting a non-NULL value into a NULL-only range, we
reset the all_nulls flag but don't update the has_nulls flag. And
because of that we then fail to return the range for IS NULL ranges.

Reproducing this is trivial:

  create table t (a int);
  create index on t using brin (a);
  insert into t values (null);
  insert into t values (1);

  set enable_seqscan  = off;
  select * from t where a is null;

This should return 1 row, but actually it returns no rows.

Attached is a patch fixing this by properly updating the has_nulls flag.

I reproduced this all the way back to 9.5, so it's a long-standing bug.
It's interesting no one noticed / reported it so far, it doesn't seem
like a particularly rare corner case.


regards

-- 
Tomas Vondra
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

Commits

  1. Show empty BRIN ranges in brin_page_items

  2. Fix handling of empty ranges and NULLs in BRIN

  3. Fix handling of NULLs when merging BRIN summaries

  4. Move IS [NOT] NULL handling from BRIN support functions