Add nbtree page deletion assertion.

Add a documenting assertion that's similar to the nearby assertion added
by commit cd8c73a3.  This conveys that the entire call to _bt_pagedel()
does no work if it isn't possible to get a descent stack for the initial
scanblkno page.

diff --git a/src/backend/access/nbtree/nbtpage.c b/src/backend/access/nbtree/nbtpage.c
index 70bac0052fc6aa51f190039edd62942279df061c..53dff326808385ffd0e638c66e1ec7eec86c7ec1 100644 (file)
--- a/src/backend/access/nbtree/nbtpage.c
+++ b/src/backend/access/nbtree/nbtpage.c
@@ -1697,6 +1697,7 @@ _bt_pagedel(Relation rel, Buffer leafbuf, TransactionId *oldestBtpoXact)
                if (_bt_leftsib_splitflag(rel, leftsib, leafblkno))
                {
                    ReleaseBuffer(leafbuf);
+                   Assert(ndeleted == 0);
                    return ndeleted;
                }