pgsql: Consider explicit incremental sort for Append and MergeAppend - Mailing list pgsql-committers

From Richard Guo
Subject pgsql: Consider explicit incremental sort for Append and MergeAppend
Date
Msg-id E1uYx2b-005Blr-0P@gemulon.postgresql.org
Whole thread Raw
List pgsql-committers
Consider explicit incremental sort for Append and MergeAppend

For an ordered Append or MergeAppend, we need to inject an explicit
sort into any subpath that is not already well enough ordered.
Currently, only explicit full sorts are considered; incremental sorts
are not yet taken into account.

In this patch, for subpaths of an ordered Append or MergeAppend, we
choose to use explicit incremental sort if it is enabled and there are
presorted keys.

The rationale is based on the assumption that incremental sort is
always faster than full sort when there are presorted keys, a premise
that has been applied in various parts of the code.  In addition, the
current cost model tends to favor incremental sort as being cheaper
than full sort in the presence of presorted keys, making it reasonable
not to consider full sort in such cases.

No backpatch as this could result in plan changes.

Author: Richard Guo <guofenglinux@gmail.com>
Reviewed-by: Andrei Lepikhov <lepihov@gmail.com>
Reviewed-by: Robert Haas <robertmhaas@gmail.com>
Discussion: https://postgr.es/m/CAMbWs4_V7a2enTR+T3pOY_YZ-FU8ZsFYym2swOz4jNMqmSgyuw@mail.gmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/55a780e9476a753354a6db887e92125c7886ca6d

Modified Files
--------------
src/backend/optimizer/path/costsize.c          | 54 ++++++++++++++-----
src/backend/optimizer/plan/createplan.c        | 66 ++++++++++++++++++++---
src/backend/optimizer/util/pathnode.c          | 73 +++++++++++++++++---------
src/include/optimizer/cost.h                   |  2 +-
src/test/regress/expected/incremental_sort.out | 40 ++++++++++++++
src/test/regress/expected/inherit.out          | 10 ++--
src/test/regress/sql/incremental_sort.sql      | 24 +++++++++
7 files changed, 217 insertions(+), 52 deletions(-)


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