Horton

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

Justin Pryzby <pryzby@telsasoft.com>

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From: Justin Pryzby <pryzby@telsasoft.com>
To: Alexander Korotkov <aekorotkov@gmail.com>
Cc: Andrei Lepikhov <a.lepikhov@postgrespro.ru>, 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: 2024-04-08T00:38:36Z
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 Mon, Apr 08, 2024 at 01:34:37AM +0300, Alexander Korotkov wrote:
> Hi!
> 
> On Mon, Apr 1, 2024 at 9:38 AM Andrei Lepikhov
> <a.lepikhov@postgrespro.ru> wrote:
> > On 28/3/2024 16:54, Alexander Korotkov wrote:
> > > 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.
> > I labelled it or_transformation_limit (see in attachment). Feel free to
> > rename it.
> > It's important to note that the limiting GUC doesn't operate
> > symmetrically for forward, OR -> SAOP, and backward SAOP -> OR
> > operations. In the forward case, it functions as you've proposed.
> > However, in the backward case, we only check whether the feature is
> > enabled or not. This is due to our existing limitation,
> > MAX_SAOP_ARRAY_SIZE, and the fact that we can't match the length of the
> > original OR list with the sizes of the resulting SAOPs. For instance, a
> > lengthy OR list with 100 elements can be transformed into 3 SAOPs, each
> > with a size of around 30 elements.
> > One aspect that requires attention is the potential inefficiency of our
> > OR -> ANY transformation when we have a number of elements less than
> > MAX_SAOP_ARRAY_SIZE. This is because we perform a reverse transformation
> > ANY -> OR at the stage of generating bitmap scans. If the BitmapScan
> > path dominates, we may have done unnecessary work. Is this an occurrence
> > that we should address?
> > But the concern above may just be a point of improvement later: We can
> > add one more strategy to the optimizer: testing each array element as an
> > OR clause; we can also provide a BitmapOr path, where SAOP is covered
> > with a minimal number of partial indexes (likewise, previous version).
> 
> I've revised the patch.  Did some beautification, improvements for
> documentation, commit messages etc.
> 
> I've pushed the 0001 patch without 0002.  I think 0001 is good by
> itself given that there is the or_to_any_transform_limit GUC option.
> The more similar OR clauses are here the more likely grouping them
> into SOAP will be a win.  But I've changed the default value to 5.

The sample config file has the wrong default

+#or_to_any_transform_limit = 0

We had a patch to catch this kind of error, but it was closed (which IMO
was itself an error).

-- 
Justin