From: Peter Geoghegan <pg@bowt.ie>
To: pgsql-committers@lists.postgresql.org
Subject: pgsql: Fix nbtree array unsatisfied inequality check.
Date: Wed, 26 Jun 2024 14:46:09 +0000
Message-ID: <E1sMTuS-0036ja-QL@gemulon.postgresql.org> (raw)
Fix nbtree array unsatisfied inequality check.
_bt_advance_array_keys didn't take sufficient care at the point where it
decides whether to start a new primitive index scan based on a call to
_bt_check_compare against finaltup (a call with the scan direction
flipped around). The final decision was conditioned on rules about how
the scan key offset sktrig that initially triggered array advancement
(passed to _bt_advance_array_keys from its _bt_checkkeys caller)
compared to the offset set by its own _bt_check_compare finaltup call.
This approach was faulty, in that it allowed _bt_advance_array_keys to
incorrectly start a new primitive index scan, that landed on the same
leaf page (on assert-enabled builds it led to an assertion failure).
In general, scans with array keys are expected to never have to read the
same leaf page more than once (barring cases involving cursors, and
cases where the scan restores a marked position for the inner side of a
merge join). This principle was established by commit 5bf748b8.
To fix, make the final decision based on whether the scan key offset set
by the _bt_check_compare finaltup call is an offset to an inequality
strategy scan key. An unsatisfied required inequality strategy scan key
indicates that all of the scan's required equality strategy scan keys
must also be satisfied by finaltup (not just by caller's tuple), and
that there is a decent chance that _bt_first will be able to reposition
the scan to a position many leaf pages ahead of the current leaf page.
Oversight in commit 5bf748b8.
Discussion: https://postgr.es/m/CAH2-Wz=DyHbcg7o6zXqzyiin8WE8vzk4tvU8Lrnh-a=EAvO0TQ@mail.gmail.com
Branch
------
master
Details
-------
https://git.postgresql.org/pg/commitdiff/486c2ea25c5e7e248c31b2dbb5db8ebcd3c7d813
Modified Files
--------------
src/backend/access/nbtree/nbtutils.c | 30 ++++++++++--------------------
1 file changed, 10 insertions(+), 20 deletions(-)
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-committers@postgresql.org
Cc: pg@bowt.ie, pgsql-committers@lists.postgresql.org
Subject: Re: pgsql: Fix nbtree array unsatisfied inequality check.
In-Reply-To: <E1sMTuS-0036ja-QL@gemulon.postgresql.org>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox