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pgsql: Always commute strategy when preprocessing DESC keys. 2+ messages / 1 participants [nested] [flat]
* pgsql: Always commute strategy when preprocessing DESC keys. @ 2025-09-12 17:23 Peter Geoghegan <pg@bowt.ie> 0 siblings, 0 replies; 2+ messages in thread From: Peter Geoghegan @ 2025-09-12 17:23 UTC (permalink / raw) To: pgsql-committers@lists.postgresql.org Always commute strategy when preprocessing DESC keys. A recently added nbtree preprocessing step failed to account for the fact that DESC columns already had their B-Tree strategy number commuted at this point in preprocessing. As a result, preprocessing could output a set of scan keys where one or more keys had the correct strategy number, but used the wrong comparison routine. To fix, make the faulty code path that looks up a more restrictive replacement operator/comparison routine commute its requested inequality strategy (while outputting the transformed strategy number as before). This makes the final transformed scan key comport with the approach preprocessing has always used to deal with DESC columns (which is described by comments above _bt_fix_scankey_strategy). Oversight in commit commit b3f1a13f, which made nbtree preprocessing perform transformations on skip array inequalities that can reduce the total number of index searches. Author: Peter Geoghegan <pg@bowt.ie> Reported-By: Natalya Aksman <natalya@timescale.com> Discussion: https://postgr.es/m/19049-b7df801e71de41b2@postgresql.org Backpatch-through: 18 Branch ------ master Details ------- https://git.postgresql.org/pg/commitdiff/796962922e6938fdad4dbf810fb2a5dfcfc5f45a Modified Files -------------- src/backend/access/nbtree/nbtpreprocesskeys.c | 24 ++++++++++++++++++------ 1 file changed, 18 insertions(+), 6 deletions(-) ^ permalink raw reply [nested|flat] 2+ messages in thread
* pgsql: Always commute strategy when preprocessing DESC keys. @ 2025-09-12 17:23 Peter Geoghegan <pg@bowt.ie> 0 siblings, 0 replies; 2+ messages in thread From: Peter Geoghegan @ 2025-09-12 17:23 UTC (permalink / raw) To: pgsql-committers@lists.postgresql.org Always commute strategy when preprocessing DESC keys. A recently added nbtree preprocessing step failed to account for the fact that DESC columns already had their B-Tree strategy number commuted at this point in preprocessing. As a result, preprocessing could output a set of scan keys where one or more keys had the correct strategy number, but used the wrong comparison routine. To fix, make the faulty code path that looks up a more restrictive replacement operator/comparison routine commute its requested inequality strategy (while outputting the transformed strategy number as before). This makes the final transformed scan key comport with the approach preprocessing has always used to deal with DESC columns (which is described by comments above _bt_fix_scankey_strategy). Oversight in commit commit b3f1a13f, which made nbtree preprocessing perform transformations on skip array inequalities that can reduce the total number of index searches. Author: Peter Geoghegan <pg@bowt.ie> Reported-By: Natalya Aksman <natalya@timescale.com> Discussion: https://postgr.es/m/19049-b7df801e71de41b2@postgresql.org Backpatch-through: 18 Branch ------ REL_18_STABLE Details ------- https://git.postgresql.org/pg/commitdiff/e457312c0d19b3d4e60f44f7260280a2788c1503 Modified Files -------------- src/backend/access/nbtree/nbtpreprocesskeys.c | 24 ++++++++++++++++++------ 1 file changed, 18 insertions(+), 6 deletions(-) ^ permalink raw reply [nested|flat] 2+ messages in thread
end of thread, other threads:[~2025-09-12 17:23 UTC | newest] Thread overview: 2+ messages (download: mbox mbox.gz follow: Atom feed) -- links below jump to the message on this page -- 2025-09-12 17:23 pgsql: Always commute strategy when preprocessing DESC keys. Peter Geoghegan <pg@bowt.ie> 2025-09-12 17:23 pgsql: Always commute strategy when preprocessing DESC keys. Peter Geoghegan <pg@bowt.ie>
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