replication: Always trigger replication in replicationProgress()

Some call sites require to skip the progressShouldReplicate() check and force
triggering replication. For example when probing a server fails because of
missing entries, the leader should retry immediately without waiting the
heartbeat timeout.

Signed-off-by: Free Ekanayaka <free@ekanayaka.io>

src/replication.c

@@ -236,10 +236,6 @@ int replicationProgress(struct raft *r, unsigned i)
     assert(server->id != r->id);
     assert(next_index >= 1);
 
-    if (!progressShouldReplicate(r, i)) {
-        return 0;
-    }
-
     /* From Section 3.5:
      *
      *   When sending an AppendEntries RPC, the leader includes the index and
@@ -321,6 +317,9 @@ static int triggerAll(struct raft *r)
             server->id != r->leader_state.promotee_id) {
             continue;
         }
+        if (!progressShouldReplicate(r, i)) {
+            continue;
+        }
         rv = replicationProgress(r, i);
         if (rv != 0 && rv != RAFT_NOCONNECTION) {
             /* This is not a critical failure, let's just log it. */
@@ -628,8 +627,10 @@ int replicationUpdate(struct raft *r,
         }
     }
 
-    /* If this follower is in pipeline mode, send it more entries. */
-    if (progressState(r, i) == PROGRESS__PIPELINE) {
+    /* If this follower is in pipeline mode, send it more entries if
+     * needed. */
+    if (progressState(r, i) == PROGRESS__PIPELINE &&
+        progressShouldReplicate(r, i)) {
         replicationProgress(r, i);
     }
 

test/integration/test_snapshot.c

@@ -187,7 +187,7 @@ TEST(snapshot,
     (void)params;
 
     /* Set very low threshold and trailing entries number */
-    SET_SNAPSHOT_THRESHOLD(3);
+    SET_SNAPSHOT_THRESHOLD(4);
     SET_SNAPSHOT_TRAILING(1);
     SET_SNAPSHOT_TIMEOUT(200);