postgres.git / summary / log / commit / refs

commit    e457312c0d19b3d4e60f44f7260280a2788c1503
Author:   Peter Geoghegan <pg@bowt.ie>
Date:     Fri Sep 12 17:22:58 2025 +0000
First released in: 18.0

    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


 src/backend/access/nbtree/nbtpreprocesskeys.c | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/src/backend/access/nbtree/nbtpreprocesskeys.c b/src/backend/access/nbtree/nbtpreprocesskeys.c
index 21c519cd108..4c9389c781a 100644
--- a/src/backend/access/nbtree/nbtpreprocesskeys.c
+++ b/src/backend/access/nbtree/nbtpreprocesskeys.c
@@ -1410,6 +1410,7 @@ _bt_skiparray_strat_decrement(IndexScanDesc scan, ScanKey arraysk,
 	Datum		orig_sk_argument = high_compare->sk_argument,
 				new_sk_argument;
 	bool		uflow;
+	int16		lookupstrat;
 
 	Assert(high_compare->sk_strategy == BTLessStrategyNumber);
 
@@ -1431,9 +1432,14 @@ _bt_skiparray_strat_decrement(IndexScanDesc scan, ScanKey arraysk,
 		return;
 	}
 
-	/* Look up <= operator (might fail) */
-	leop = get_opfamily_member(opfamily, opcintype, opcintype,
-							   BTLessEqualStrategyNumber);
+	/*
+	 * Look up <= operator (might fail), accounting for the fact that a
+	 * high_compare on a DESC column already had its strategy commuted
+	 */
+	lookupstrat = BTLessEqualStrategyNumber;
+	if (high_compare->sk_flags & SK_BT_DESC)
+		lookupstrat = BTGreaterEqualStrategyNumber; /* commute this too */
+	leop = get_opfamily_member(opfamily, opcintype, opcintype, lookupstrat);
 	if (!OidIsValid(leop))
 		return;
 	cmp_proc = get_opcode(leop);
@@ -1462,6 +1468,7 @@ _bt_skiparray_strat_increment(IndexScanDesc scan, ScanKey arraysk,
 	Datum		orig_sk_argument = low_compare->sk_argument,
 				new_sk_argument;
 	bool		oflow;
+	int16		lookupstrat;
 
 	Assert(low_compare->sk_strategy == BTGreaterStrategyNumber);
 
@@ -1483,9 +1490,14 @@ _bt_skiparray_strat_increment(IndexScanDesc scan, ScanKey arraysk,
 		return;
 	}
 
-	/* Look up >= operator (might fail) */
-	geop = get_opfamily_member(opfamily, opcintype, opcintype,
-							   BTGreaterEqualStrategyNumber);
+	/*
+	 * Look up >= operator (might fail), accounting for the fact that a
+	 * low_compare on a DESC column already had its strategy commuted
+	 */
+	lookupstrat = BTGreaterEqualStrategyNumber;
+	if (low_compare->sk_flags & SK_BT_DESC)
+		lookupstrat = BTLessEqualStrategyNumber; /* commute this too */
+	geop = get_opfamily_member(opfamily, opcintype, opcintype, lookupstrat);
 	if (!OidIsValid(geop))
 		return;
 	cmp_proc = get_opcode(geop);


[parent: 3c0018a6f417]