From d9280942f4ae7556da4384df596bc599207fceae Mon Sep 17 00:00:00 2001 From: Andrey Rachitskiy Date: Tue, 25 Aug 2026 00:20:18 +0500 Subject: [PATCH 1/2] Reject index-only scans when the index cannot return any columns If the query needs no heap columns and no index column is returnable, check_index_only() still succeeds because bms_is_subset(empty, empty) is true. Track any_canreturn while building the key-column bitmap and reject index-only scans when none are returnable (including expression columns, which the bitmap omits). Bug: 19638 Author: Andrey Rachitskiy Reported-by: Manuel Reyes Bravo Discussion: https://www.postgresql.org/message-id/19638-277d0f73dfaeaec8@postgresql.org --- src/backend/optimizer/path/indxpath.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-) diff --git a/src/backend/optimizer/path/indxpath.c b/src/backend/optimizer/path/indxpath.c index 3f5d4fa3182..0d4b37149d1 100644 --- a/src/backend/optimizer/path/indxpath.c +++ b/src/backend/optimizer/path/indxpath.c @@ -2226,6 +2226,7 @@ static bool check_index_only(RelOptInfo *rel, IndexOptInfo *index) { bool result; + bool any_canreturn; Bitmapset *attrs_used = NULL; Bitmapset *index_canreturn_attrs = NULL; ListCell *lc; @@ -2269,9 +2270,14 @@ check_index_only(RelOptInfo *rel, IndexOptInfo *index) * Construct a bitmapset of columns that the index can return back in an * index-only scan. */ + any_canreturn = false; for (i = 0; i < index->ncolumns; i++) { int attno = index->indexkeys[i]; + bool col_canreturn = index->canreturn[i]; + + if (col_canreturn) + any_canreturn = true; /* * For the moment, we just ignore index expressions. It might be nice @@ -2280,7 +2286,7 @@ check_index_only(RelOptInfo *rel, IndexOptInfo *index) if (attno == 0) continue; - if (index->canreturn[i]) + if (col_canreturn) index_canreturn_attrs = bms_add_member(index_canreturn_attrs, attno - FirstLowInvalidHeapAttributeNumber); @@ -2289,6 +2295,15 @@ check_index_only(RelOptInfo *rel, IndexOptInfo *index) /* Do we have all the necessary attributes? */ result = bms_is_subset(attrs_used, index_canreturn_attrs); + /* + * bms_is_subset() is true when attrs_used is empty, even if the index + * returns nothing. That would allow a broken index-only scan for AMs + * with amcanreturn == NULL. Expression columns can be returnable even + * when the key-column bitmap is empty, so test canreturn[] directly. + */ + if (result && !any_canreturn) + result = false; + bms_free(attrs_used); bms_free(index_canreturn_attrs); -- 2.53.0