Horton

Re: POC, WIP: OR-clause support for indexes

Peter Geoghegan <pg@bowt.ie>

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From: Peter Geoghegan <pg@bowt.ie>
To: "a.rybakina" <a.rybakina@postgrespro.ru>
Cc: "Finnerty, Jim" <jfinnert@amazon.com>, Marcos Pegoraro <marcos@f10.com.br>, Andrey Lepikhov <a.lepikhov@postgrespro.ru>, pgsql-hackers@postgresql.org, teodor@sigaev.ru, Ranier Vilela <ranier.vf@gmail.com>, Tomas Vondra <tomas.vondra@enterprisedb.com>
Date: 2023-08-20T22:42:39Z
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. Make group_similar_or_args() reorder clause list as little as possible

  2. Allow usage of match_orclause_to_indexcol() for joins

  3. Skip not SOAP-supported indexes while transforming an OR clause into SAOP

  4. Remove the wrong assertion from match_orclause_to_indexcol()

  5. Teach bitmap path generation about transforming OR-clauses to SAOP's

  6. Transform OR-clauses to SAOP's during index matching

  7. Fix the value of or_to_any_transform_limit in postgresql.conf.sample

  8. Transform OR clauses to ANY expression

  9. MergeAttributes code deduplication

  10. SEARCH and CYCLE clauses

  11. Improve estimation of OR clauses using extended statistics.

  12. Teach btree to handle ScalarArrayOpExpr quals natively.

  13. Revise collation derivation method and expression-tree representation.

  14. Instead of trying to force WHERE clauses into CNF or DNF normal form,

On Thu, Aug 17, 2023 at 3:08 AM a.rybakina <a.rybakina@postgrespro.ru> wrote:
> But now I see an interesting transformation, which was the most interesting for me.
>
> EXPLAIN (COSTS OFF) SELECT * FROM tenk1 WHERE thousand = 42 AND (tenthous = 1 OR tenthous = 3 OR tenthous = 42);

It would be even more interesting if it could be an index-only scan as
a result of the transformation. For example, we could use an
index-only scan with this query (once your patch was in place):

"SELECT thousand, tenthous FROM tenk1 WHERE thousand = 42 AND
(tenthous = 1 OR tenthous = 3 OR tenthous = 42)"

Index-only scans were the original motivation for adding native
ScalarArrayExprOp support to nbtree (in 2011 commit 9e8da0f7), in
fact.

As I suggested earlier, I suspect that there is too much planner logic
that targets BitmapOrs specifically -- maybe even selectivity
estimation/restrictinfo stuff.

PS I wonder if the correctness issues that you saw could be related to
eval_const_expressions(), since "the planner assumes that this
[eval_const_expressions] will always flatten nested AND and OR clauses
into N-argument form". See its subroutines simplify_or_arguments() and
simplify_and_arguments().

-- 
Peter Geoghegan