Fix incorrect return value in brin_minmax_multi_distance_numeric().

tglsfdc · tglsfdc · commit b9279058a3ca · 2025-08-05T16:51:10.000-04:00
The result of "DirectFunctionCall1(numeric_float8, d)" is already in Datum form, but the code was incorrectly applying PG_RETURN_FLOAT8() to it. On machines where float8 is pass-by-reference, this would result in complete garbage, since an unpredictable pointer value would be treated as an integer and then converted to float. It's not entirely clear how much of a problem would ensue on 64-bit hardware, but certainly interpreting a float8 bitpattern as uint64 and then converting that to float isn't the intended behavior. As luck would have it, even the complete-garbage case doesn't break BRIN indexes, since the results are only used to make choices about how to merge values into ranges: at worst, we'd make poor choices resulting in an inefficient index. Doubtless that explains the lack of field complaints. However, users with BRIN indexes that use the numeric_minmax_multi_ops opclass may wish to reindex in hopes of making their indexes more efficient. Author: Peter Eisentraut <peter@eisentraut.org> Co-authored-by: Tom Lane <tgl@sss.pgh.pa.us> Discussion: https://postgr.es/m/2093712.1753983215@sss.pgh.pa.us Backpatch-through: 14
diff --git a/src/backend/access/brin/brin_minmax_multi.c b/src/backend/access/brin/brin_minmax_multi.c
@@ -2027,7 +2027,7 @@ brin_minmax_multi_distance_numeric(PG_FUNCTION_ARGS)
 
 	d = DirectFunctionCall2(numeric_sub, a2, a1);	/* a2 - a1 */
 
-	PG_RETURN_FLOAT8(DirectFunctionCall1(numeric_float8, d));
+	PG_RETURN_DATUM(DirectFunctionCall1(numeric_float8, d));
 }
 
 /*

Original file line number	Diff line number	Diff line change
`@@ -2027,7 +2027,7 @@ brin_minmax_multi_distance_numeric(PG_FUNCTION_ARGS)`
`2027`	`2027`
`2028`	`2028`	`d = DirectFunctionCall2(numeric_sub, a2, a1); /* a2 - a1 */`
`2029`	`2029`
`2030`		`- PG_RETURN_FLOAT8(DirectFunctionCall1(numeric_float8, d));`
	`2030`	`+ PG_RETURN_DATUM(DirectFunctionCall1(numeric_float8, d));`
`2031`	`2031`	`}`
`2032`	`2032`
`2033`	`2033`	`/*`