pgsql: Skip checking of scan keys required for directional scan in B-tr - Mailing list pgsql-committers

From Alexander Korotkov
Subject pgsql: Skip checking of scan keys required for directional scan in B-tr
Date
Msg-id E1qofSq-000Iff-8c@gemulon.postgresql.org
Whole thread Raw
List pgsql-committers
Skip checking of scan keys required for directional scan in B-tree

Currently, B-tree code matches every scan key to every item on the page.
Imagine the ordered B-tree scan for the query like this.

SELECT * FROM tbl WHERE col > 'a' AND col < 'b' ORDER BY col;

The (col > 'a') scan key will be always matched once we find the location to
start the scan.  The (col < 'b') scan key will match every item on the page
as long as it matches the last item on the page.

This patch implements prechecking of the scan keys required for directional
scan on beginning of page scan.  If precheck is successful we can skip this
scan keys check for the items on the page.  That could lead to significant
acceleration especially if the comparison operator is expensive.

Idea from patch by Konstantin Knizhnik.

Discussion: https://postgr.es/m/079c3f8e-3371-abe2-e93c-fc8a0ae3f571%40garret.ru
Reviewed-by: Peter Geoghegan, Pavel Borisov

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/e0b1ee17dc3a38ba17fee0fd58b7b834ec934259

Modified Files
--------------
src/backend/access/nbtree/nbtree.c    |  1 +
src/backend/access/nbtree/nbtsearch.c | 70 +++++++++++++++++++++++++++++++++--
src/backend/access/nbtree/nbtutils.c  | 59 ++++++++++++++++++++++-------
src/include/access/nbtree.h           |  6 ++-
4 files changed, 119 insertions(+), 17 deletions(-)


pgsql-committers by date:

Previous
From: Heikki Linnakangas
Date:
Subject: pgsql: Fix crash on syslogger startup
Next
From: Etsuro Fujita
Date:
Subject: pgsql: Remove extra parenthesis from comment.