ITS#8258 fix rebalance/split

The tree height can also increase during rebalance, not just shrink.
This can happen if update_key needs to split a parent branch page.

libraries/liblmdb/mdb.c

@@ -7845,9 +7845,9 @@ mdb_page_merge(MDB_cursor *csrc, MDB_cursor *cdst)
 		uint16_t depth = cdst->mc_db->md_depth;
 		mdb_cursor_pop(cdst);
 		rc = mdb_rebalance(cdst);
-		/* Did the tree shrink? */
-		if (depth > cdst->mc_db->md_depth)
-			snum--;
+		/* Did the tree height change? */
+		if (depth != cdst->mc_db->md_depth)
+			snum += cdst->mc_db->md_depth - depth;
 		cdst->mc_snum = snum;
 		cdst->mc_top = snum-1;
 	}
@@ -8039,7 +8039,7 @@ mdb_rebalance(MDB_cursor *mc)
 	 */
 	if (PAGEFILL(mc->mc_txn->mt_env, mn.mc_pg[mn.mc_top]) >= thresh && NUMKEYS(mn.mc_pg[mn.mc_top]) > minkeys) {
 		rc = mdb_node_move(&mn, mc);
-		if (mc->mc_ki[ptop]) {
+		if (mc->mc_ki[mc->mc_top-1]) {
 			oldki++;
 		}
 	} else {
@@ -8253,8 +8253,7 @@ mdb_page_split(MDB_cursor *mc, MDB_val *newkey, MDB_val *newdata, pgno_t newpgno
 		mc->mc_ki[0] = 0;
 		mc->mc_db->md_root = pp->mp_pgno;
 		DPRINTF(("root split! new root = %"Z"u", pp->mp_pgno));
-		mc->mc_db->md_depth++;
-		new_root = 1;
+		new_root = mc->mc_db->md_depth++;
 
 		/* Add left (implicit) pointer. */
 		if ((rc = mdb_node_add(mc, 0, NULL, NULL, mp->mp_pgno, 0)) != MDB_SUCCESS) {
@@ -8567,7 +8566,7 @@ mdb_page_split(MDB_cursor *mc, MDB_val *newkey, MDB_val *newdata, pgno_t newpgno
 			if (new_root) {
 				int k;
 				/* root split */
-				for (k=m3->mc_top; k>=0; k--) {
+				for (k=new_root; k>=0; k--) {
 					m3->mc_ki[k+1] = m3->mc_ki[k];
 					m3->mc_pg[k+1] = m3->mc_pg[k];
 				}