Horton

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

Alexander Korotkov <aekorotkov@gmail.com>

View thread
From: Alexander Korotkov <aekorotkov@gmail.com>
To: Andrei Lepikhov <a.lepikhov@postgrespro.ru>
Cc: jian he <jian.universality@gmail.com>, Alena Rybakina <a.rybakina@postgrespro.ru>, Robert Haas <robertmhaas@gmail.com>, pgsql-hackers@postgresql.org, Peter Geoghegan <pg@bowt.ie>, "Finnerty, Jim" <jfinnert@amazon.com>, Marcos Pegoraro <marcos@f10.com.br>, teodor@sigaev.ru, Tomas Vondra <tomas.vondra@enterprisedb.com>, Peter Eisentraut <peter@eisentraut.org>, Ranier Vilela <ranier.vf@gmail.com>
Date: 2024-03-28T13:54:57Z
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 Tue, Mar 19, 2024 at 7:17 AM Andrei Lepikhov
<a.lepikhov@postgrespro.ru> wrote:
> On 14/3/2024 16:31, Alexander Korotkov wrote:
> > On Wed, Mar 13, 2024 at 2:16 PM Andrei Lepikhov
> > As you can see this case is not related to partial indexes.  Just no
> > index selective for the whole query.  However, splitting scan by the OR
> > qual lets use a combination of two selective indexes.
> I have rewritten the 0002-* patch according to your concern. A candidate
> and some thoughts are attached.
> As I see, we have a problem here: expanding each array and trying to
> apply an element to each index can result in a lengthy planning stage.
> Also, an index scan with the SAOP may potentially be more effective than
> with the list of OR clauses.
> Originally, the transformation's purpose was to reduce a query's
> complexity and the number of optimization ways to speed up planning and
> (sometimes) execution. Here, we reduce planning complexity only in the
> case of an array size larger than MAX_SAOP_ARRAY_SIZE.
> Maybe we can fall back to the previous version of the second patch,
> keeping in mind that someone who wants to get maximum profit from the
> BitmapOr scan of multiple indexes can just disable this optimization,
> enabling deep search of the most optimal scanning way?
> As a compromise solution, I propose adding one more option to the
> previous version: if an element doesn't fit any partial index, try to
> cover it with a plain index.
> In this case, we still do not guarantee the most optimal fit of elements
> to the set of indexes, but we speed up planning. Does that make sense?

Thank you for your research Andrei.  Now things get more clear on the
advantages and disadvantages of this transformation.

The current patch has a boolean guc enable_or_transformation.
However, when we have just a few ORs to be transformated, then we
should get less performance gain from the transformation and higher
chances to lose a good bitmap scan plan from that.  When there is a
huge list of ORs to be transformed, then the performance gain is
greater and it is less likely we could lose a good bitmap scan plan.

What do you think about introducing a GUC threshold value: the minimum
size of list to do OR-to-ANY transformation?
min_list_or_transformation or something.

------
Regards,
Alexander Korotkov