Fix calculation in brin_minmax_multi_distance_date

tvondra · tvondra · commit e7965226d551 · 2023-10-27T18:28:19.000+02:00
When calculating the distance between date values, make sure to subtract them in the right order, i.e. (larger - smaller). The distance is used to determine which values to merge, and is expected to be a positive value. The code unfortunately did the subtraction in the opposite order, i.e. (smaller - larger), thus producing negative values and merging values the most distant values first. The resulting index is correct (i.e. produces correct results), but may be significantly less efficient. This affects all minmax-multi indexes on date columns. Backpatch to 14, where minmax-multi indexes were introduced. Reported-by: Ashutosh Bapat Reviewed-by: Ashutosh Bapat, Dean Rasheed Backpatch-through: 14 Discussion: https://postgr.es/m/eef0ea8c-4aaa-8d0d-027f-58b1f35dd170@enterprisedb.com
diff --git a/src/backend/access/brin/brin_minmax_multi.c b/src/backend/access/brin/brin_minmax_multi.c
@@ -2075,13 +2075,18 @@ brin_minmax_multi_distance_uuid(PG_FUNCTION_ARGS)
 Datum
 brin_minmax_multi_distance_date(PG_FUNCTION_ARGS)
 {
+	float8		delta = 0;
 	DateADT		dateVal1 = PG_GETARG_DATEADT(0);
 	DateADT		dateVal2 = PG_GETARG_DATEADT(1);
 
 	if (DATE_NOT_FINITE(dateVal1) || DATE_NOT_FINITE(dateVal2))
 		PG_RETURN_FLOAT8(0);
 
-	PG_RETURN_FLOAT8(dateVal1 - dateVal2);
+	delta = (float8) dateVal2 - (float8) dateVal1;
+
+	Assert(delta >= 0);
+
+	PG_RETURN_FLOAT8(delta);
 }
 
 /*
diff --git a/src/test/regress/expected/brin_multi.out b/src/test/regress/expected/brin_multi.out
@@ -479,5 +479,25 @@ SELECT '294276-12-01 00:00:01'::timestamptz + (i || ' seconds')::interval
   FROM generate_series(1,30) s(i);
 CREATE INDEX ON brin_timestamp_test USING brin (a timestamptz_minmax_multi_ops) WITH (pages_per_range=1);
 DROP TABLE brin_timestamp_test;
+-- test overflows during CREATE INDEX with extreme date values
+CREATE TABLE brin_date_test(a DATE);
+-- insert values close to date minimum
+INSERT INTO brin_date_test SELECT '4713-01-01 BC'::date + i FROM generate_series(1, 30) s(i);
+-- insert values close to date minimum
+INSERT INTO brin_date_test SELECT '5874897-12-01'::date + i FROM generate_series(1, 30) s(i);
+CREATE INDEX ON brin_date_test USING brin (a date_minmax_multi_ops) WITH (pages_per_range=1);
+SET enable_seqscan = off;
+-- make sure the ranges were built correctly and 2023-01-01 eliminates all
+EXPLAIN (ANALYZE, TIMING OFF, COSTS OFF, SUMMARY OFF)
+SELECT * FROM brin_date_test WHERE a = '2023-01-01'::date;
+                               QUERY PLAN                                
+-------------------------------------------------------------------------
+ Bitmap Heap Scan on brin_date_test (actual rows=0 loops=1)
+   Recheck Cond: (a = '2023-01-01'::date)
+   ->  Bitmap Index Scan on brin_date_test_a_idx (actual rows=0 loops=1)
+         Index Cond: (a = '2023-01-01'::date)
+(4 rows)
+
+DROP TABLE brin_date_test;
 RESET enable_seqscan;
 RESET datestyle;
diff --git a/src/test/regress/sql/brin_multi.sql b/src/test/regress/sql/brin_multi.sql
@@ -440,5 +440,23 @@ SELECT '294276-12-01 00:00:01'::timestamptz + (i || ' seconds')::interval
 CREATE INDEX ON brin_timestamp_test USING brin (a timestamptz_minmax_multi_ops) WITH (pages_per_range=1);
 DROP TABLE brin_timestamp_test;
 
+-- test overflows during CREATE INDEX with extreme date values
+CREATE TABLE brin_date_test(a DATE);
+
+-- insert values close to date minimum
+INSERT INTO brin_date_test SELECT '4713-01-01 BC'::date + i FROM generate_series(1, 30) s(i);
+
+-- insert values close to date minimum
+INSERT INTO brin_date_test SELECT '5874897-12-01'::date + i FROM generate_series(1, 30) s(i);
+
+CREATE INDEX ON brin_date_test USING brin (a date_minmax_multi_ops) WITH (pages_per_range=1);
+
+SET enable_seqscan = off;
+
+-- make sure the ranges were built correctly and 2023-01-01 eliminates all
+EXPLAIN (ANALYZE, TIMING OFF, COSTS OFF, SUMMARY OFF)
+SELECT * FROM brin_date_test WHERE a = '2023-01-01'::date;
+
+DROP TABLE brin_date_test;
 RESET enable_seqscan;
 RESET datestyle;
