Update nbits_set in brin_bloom_union

tvondra · tvondra · commit ccd8f0fa1e54 · 2024-04-14T18:17:09.000+02:00
Properly update the number of bits set in the bitmap after merging the filters in brin_bloom_union. This is mostly harmless, as the counter is used only in the output function, which means pageinspect may show incorrect information about the BRIN summary. The counter does not affect correctness. Discovered while adding a regression test comparing indexes built with and without parallelism. The parallel index builds exercise the union procedure when merging results from workers, which is otherwise very hard to do in a test. Which is why this went unnoticed until now. Backpatch through 14, where the BRIN bloom opclasses were introduced. Backpatch-through: 14 Discussion: https://postgr.es/m/1df00a66-db5a-4e66-809a-99b386a06d86%40enterprisedb.com
diff --git a/src/backend/access/brin/brin_bloom.c b/src/backend/access/brin/brin_bloom.c
@@ -660,6 +660,9 @@ brin_bloom_union(PG_FUNCTION_ARGS)
 	for (i = 0; i < nbytes; i++)
 		filter_a->data[i] |= filter_b->data[i];
 
+	/* update the number of bits set in the filter */
+	filter_a->nbits_set = pg_popcount((const char *) filter_a->data, nbytes);
+
 	PG_RETURN_VOID();
 }
 

Original file line number	Diff line number	Diff line change
`@@ -660,6 +660,9 @@ brin_bloom_union(PG_FUNCTION_ARGS)`
`660`	`660`	`for (i = 0; i < nbytes; i++)`
`661`	`661`	`filter_a->data[i] \|= filter_b->data[i];`
`662`	`662`
	`663`	`+ /* update the number of bits set in the filter */`
	`664`	`+ filter_a->nbits_set = pg_popcount((const char *) filter_a->data, nbytes);`
	`665`	`+`
`663`	`666`	`PG_RETURN_VOID();`
`664`	`667`	`}`
`665`	`668`