With the new LMDB cache code, objects with zero registered handlers are
not removed from the cache any longer if they contain child objects in
the dntree.

Reproducible on a Master with S4-Connector:

## 1. Preparation to initialize the cache as usual,
##    this is not required if the system is installed/updated normally
ucr unset connector/s4/listener/disabled
service univention-directory-listener stop
/usr/sbin/univention-directory-listener -F -d 2 -b dc=ar41i1,dc=qa -m /usr/lib/univention-directory-listener/system -c /var/lib/univention-directory-listener -ZZ -x -D cn=admin,dc=ar41i1,dc=qa -y /etc/ldap.secret -g -i

## 2. Resync all modules:
ucr set connector/s4/listener/disabled=yes
service univention-directory-listener stop
rm /var/lib/univention-directory-listener/handlers/*
/usr/sbin/univention-directory-listener -F -d 2 -b dc=ar41i1,dc=qa -m /usr/lib/univention-directory-listener/system -c /var/lib/univention-directory-listener -ZZ -x -D cn=admin,dc=ar41i1,dc=qa -y /etc/ldap.secret -i

## Since replication.py is not present on the Master, the s4-connector handler
## seems to be the only one that was registered on container objects. Since
## we disabled that module, they are not removed any longer
09.03.17 11:34:12.772  LISTENER    ( WARN    ) : initializing module s4-connector
09.03.17 11:34:12.773  LISTENER    ( ERROR   ) : dntree_del_id: delete failed: subordinate objects must be deleted first
09.03.17 11:34:12.773  LISTENER    ( ERROR   ) : cache_delete_entry: aborting delete: dc=ar41i1,dc=qa
09.03.17 11:34:12.774  LISTENER    ( ERROR   ) : dntree_del_id: delete failed: subordinate objects must be deleted first
09.03.17 11:34:12.774  LISTENER    ( ERROR   ) : cache_delete_entry: aborting delete: cn=computers,dc=ar41i1,dc=qa
09.03.17 11:34:12.774  LISTENER    ( ERROR   ) : dntree_del_id: delete failed: subordinate objects must be deleted first
09.03.17 11:34:12.774  LISTENER    ( ERROR   ) : cache_delete_entry: aborting delete: cn=dc,cn=computers,dc=ar41i1,dc=qa
09.03.17 11:34:12.775  LISTENER    ( ERROR   ) : dntree_del_id: delete failed: subordinate objects must be deleted first
09.03.17 11:34:12.775  LISTENER    ( ERROR   ) : cache_delete_entry: aborting delete: cn=builtin,dc=ar41i1,dc=qa
09.03.17 11:34:12.775  LISTENER    ( ERROR   ) : dntree_del_id: delete failed: subordinate objects must be deleted first


Index: src/cache.c
===================================================================
--- src/cache.c	(Revision 77488)
+++ src/cache.c	(Arbeitskopie)
@@ -560,13 +560,8 @@
 	}
 
 	rv = dntree_del_id(*id2dn_cursor_pp, dnid);
-	if (rv != MDB_SUCCESS) {
-		signals_unblock();
-		return rv;
-	}
 
 	signals_unblock();
-
 	return rv;
 }
 
Index: src/cache_dn.c
===================================================================
--- src/cache_dn.c	(Revision 77393)
+++ src/cache_dn.c	(Arbeitskopie)
@@ -317,7 +353,9 @@
 	dbi = mdb_cursor_dbi(write_cursor_p);
 	rv = mdb_cursor_open(txn, dbi, &local_read_cursor_p);
 	if (rv != MDB_SUCCESS) {
-		univention_debug(UV_DEBUG_LISTENER, UV_DEBUG_ERROR, "%s: mdb_cursor_open: %s (%d)", __func__, ldap_err2string(rv), rv);
+		univention_debug(UV_DEBUG_LISTENER, UV_DEBUG_ERROR,
+		                 "%s: mdb_cursor_open: %s (%d)",
+		                 __func__, ldap_err2string(rv), rv);
 		abort();
 		return rv;
 	}
@@ -324,12 +362,15 @@
 
 	rv = dntree_has_children(local_read_cursor_p, dnid);
 	if (rv == MDB_SUCCESS) {
-		univention_debug(UV_DEBUG_LISTENER, UV_DEBUG_ERROR, "%s: delete failed:"
-		                                                    " subordinate objects must be deleted first",
+		univention_debug(UV_DEBUG_LISTENER, UV_DEBUG_INFO,
+		                 "%s: delete failed:"
+		                 " subordinate objects must be deleted first",
 		                 __func__);
-		return -1;
+		return MDB_SUCCESS;
 	} else if (rv != MDB_NOTFOUND) {
-		univention_debug(UV_DEBUG_LISTENER, UV_DEBUG_ERROR, "%s: dntree_has_children failed: %s (%d)", __func__, mdb_strerror(rv), rv);
+		univention_debug(UV_DEBUG_LISTENER, UV_DEBUG_ERROR,
+		                 "%s: dntree_has_children failed: %s (%d)",
+		                 __func__, mdb_strerror(rv), rv);
 		abort();
 		return -1;
 	}
@@ -344,11 +385,24 @@
 		rv = mdb_cursor_get(write_cursor_p, &key, &data, MDB_SET);
 		if (rv == MDB_SUCCESS) {
 			rv = mdb_cursor_del(write_cursor_p, 0);
+			if (rv != MDB_SUCCESS)
+				univention_debug(UV_DEBUG_LISTENER, UV_DEBUG_ERROR,
+				                 "%s: failed for node id=%lu: %s (%d)",
+				                 __func__, dnid, mdb_strerror(rv), rv);
+				abort();
+			}
 		}
+	} else {
+		univention_debug(UV_DEBUG_LISTENER, UV_DEBUG_ERROR,
+		                 "%s: failed for link id=%lu: %s (%d)",
+		                 __func__, dnid, mdb_strerror(rv), rv);
+		abort();
 	}
 
 	if (rv == MDB_SUCCESS) {
-		univention_debug(UV_DEBUG_LISTENER, UV_DEBUG_INFO, "%s: deleted id=%lu", __func__, dnid);
+		univention_debug(UV_DEBUG_LISTENER, UV_DEBUG_INFO,
+		                 "%s: deleted id=%lu",
+		                 __func__, dnid);
 	}
 
 	return rv;