nbtree: Demote incomplete split "can't happen" error.
Only a basic logic bug in a _bt_insertonpg() caller could lead to a
violation of this invariant (index corruption won't do it).  A "can't
happen" error seems inappropriate (it is arbitrary at best).
Demote the error to a simple assertion.  This matches similar nearby
sanity checks.
@@ -1129,6 +1129,8 @@ _bt_insertonpg(Relation rel,
IndexRelationGetNumberOfKeyAttributes(rel));
Assert(!BTreeTupleIsPosting(itup));
Assert(MAXALIGN(IndexTupleSize(itup)) == itemsz);
+ /* Caller must always finish incomplete split for us */
+ Assert(!P_INCOMPLETE_SPLIT(lpageop));
/*
* Every internal page should have exactly one negative infinity item at
@@ -1138,11 +1140,6 @@ _bt_insertonpg(Relation rel,
*/
Assert(P_ISLEAF(lpageop) || newitemoff > P_FIRSTDATAKEY(lpageop));
- /* The caller should've finished any incomplete splits already. */
- if (P_INCOMPLETE_SPLIT(lpageop))
- elog(ERROR, "cannot insert to incompletely split page %u",
- BufferGetBlockNumber(buf));
-
/*
* Do we need to split an existing posting list item?
*/
