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commit    02699bc1fd3b7fccba2e6b55189a148ef69b8a00
Author:   Tomas Vondra <tomas.vondra@postgresql.org>
Date:     Fri Dec 30 18:44:48 2022 +0000
First released in: 16.0, 14.7, 15.2

    Fix assert in BRIN build_distances
    
    When brin_minmax_multi_union merges summaries, we may end up with just a
    single range after merge_overlapping_ranges. The summaries may contain
    just one range each, and they may overlap (or be exactly the same).
    
    With a single range there's no distance to calculate, but we happen to
    call build_distances anyway - which is fine, we don't calculate the
    distance in this case, except that with asserts this failed due to a
    check there are at least two ranges.
    
    The assert is unnecessarily strict, so relax it a bit and bail out if
    there's just a single range. The relaxed assert would be enough, but
    this way we don't allocate unnecessary memory for distance.
    
    Backpatch to 14, where minmax-multi opclasses were introduced.
    
    Reported-by: Jaime Casanova
    Backpatch-through: 14
    Discussion: https://postgr.es/m/YzVA55qS0hgz8P3r@ahch-to


 src/backend/access/brin/brin_minmax_multi.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/backend/access/brin/brin_minmax_multi.c b/src/backend/access/brin/brin_minmax_multi.c
index 9a0bcf6698d..def864e2fa9 100644
--- a/src/backend/access/brin/brin_minmax_multi.c
+++ b/src/backend/access/brin/brin_minmax_multi.c
@@ -1335,7 +1335,11 @@ build_distances(FmgrInfo *distanceFn, Oid colloid,
 	int			ndistances;
 	DistanceValue *distances;
 
-	Assert(neranges >= 2);
+	Assert(neranges > 0);
+
+	/* If there's only a single range, there's no distance to calculate. */
+	if (neranges == 1)
+		return NULL;
 
 	ndistances = (neranges - 1);
 	distances = (DistanceValue *) palloc0(sizeof(DistanceValue) * ndistances);


[parent: 7aa81c61ec8f]