DAOS-333 server: Don't remove later entries for matching AEs

If an AE request's previous entry matches the follower's, then the
follower doesn't need to truncate its log at prev_log_idx. When the
follower checks if the other entries in the AE request are consistent
with its local ones, it already takes care of truncating at any
inconsistency. If any later entries not covered by this AE request are
inconsistent, future AE requests shall truncate them.

Signed-off-by: Li Wei <wei.g.li@intel.com>

src/raft_server.c

@@ -395,21 +395,11 @@ int raft_recv_appendentries(
         }
     }
 
+    r->current_idx = ae->prev_log_idx;
+
     /* 3. If an existing entry conflicts with a new one (same index
        but different terms), delete the existing entry and all that
        follow it (§5.3) */
-    if (0 < ae->prev_log_idx && ae->prev_log_idx + 1 < raft_get_current_idx(me_))
-    {
-        /* Heartbeats shouldn't cause logs to be deleted. Heartbeats might be 
-         * sent before the leader received the last appendentries response */
-        if (ae->n_entries != 0 &&
-                /* this is an old out-of-order appendentry message */
-                me->commit_idx < ae->prev_log_idx + 1)
-            raft_delete_entry_from_idx(me_, ae->prev_log_idx + 1);
-    }
-
-    r->current_idx = ae->prev_log_idx;
-
     int i;
     for (i = 0; i < ae->n_entries; i++)
     {

tests/test_server.c

@@ -1337,7 +1337,7 @@ void TestRaft_follower_recv_appendentries_delete_entries_if_conflict_with_new_en
     CuAssertTrue(tc, !strncmp(ety_appended->data.buf, str4, 3));
 }
 
-void TestRaft_follower_recv_appendentries_delete_entries_if_current_idx_greater_than_prev_log_idx(
+void TestRaft_follower_recv_appendentries_delete_entries_if_conflict_with_new_entries_greater_than_prev_log_idx(
     CuTest * tc)
 {
     raft_cbs_t funcs = {