Improve checks to prevent unneeded replication triggers

(cherry picked from commit 50a588c38b)
(cherry picked from commit d21a0c9582)
(cherry picked from commit 64e7c5bbd0)
(cherry picked from commit 48881ae10a)

include/RaftManager.h

@@ -91,6 +91,15 @@ public:
      */
     void replicate_log(ReplicaRequest * rr);
 
+    /**
+     *  Allocate a replica request fot the given index.
+     *    @param rindex of the record for the request
+     */
+	void replicate_allocate(int rindex)
+	{
+		requests.allocate(rindex);
+	}
+
     /**
      *  Finalizes the Raft Consensus Manager
      */

include/ReplicaRequest.h

@@ -135,7 +135,7 @@ public:
 
         std::map<int, ReplicaRequest *>::iterator it = requests.find(rindex);
 
-        if ( it != requests.end() )
+        if ( it != requests.end() && it->second != 0 )
         {
             it->second->add_replica();
 
@@ -152,6 +152,20 @@ public:
         return to_commit;
     }
 
+    /**
+     *  Allocated an empty replica request. It marks a writer thread will wait
+     *  on this request.
+     *    @param rindex of the request
+     */
+    void allocate(int rindex)
+    {
+        pthread_mutex_lock(&mutex);
+
+        requests.insert(std::make_pair(rindex, (ReplicaRequest*) 0));
+
+        pthread_mutex_unlock(&mutex);
+    }
+
     /**
      * Set the replication request associated to this index. If there is no
      * previous request associated to the index it is created.
@@ -168,6 +182,28 @@ public:
         {
             requests.insert(std::make_pair(rindex, rr));
         }
+        else if ( it->second == 0 )
+        {
+            it->second = rr;
+        }
+
+        pthread_mutex_unlock(&mutex);
+    }
+
+    /**
+     *  Remove a replication request associated to this index
+     *   @param rindex of the request
+     */
+    void remove(int rindex)
+    {
+        pthread_mutex_lock(&mutex);
+
+        std::map<int, ReplicaRequest *>::iterator it = requests.find(rindex);
+
+        if ( it != requests.end() )
+        {
+            requests.erase(it);
+        }
 
         pthread_mutex_unlock(&mutex);
     }
@@ -200,6 +236,23 @@ public:
         pthread_mutex_unlock(&mutex);
     }
 
+    /**
+     *  @return true if a replica request is set for this index
+     */
+    bool is_replicable(int rindex)
+    {
+        pthread_mutex_lock(&mutex);
+
+        std::map<int, ReplicaRequest *>::iterator it = requests.find(rindex);
+
+        bool rc = it == requests.end() || 
+            (it != requests.end() && it->second != 0);
+
+        pthread_mutex_unlock(&mutex);
+
+        return rc;
+    }
+
 private:
 
     pthread_mutex_t mutex;

src/raft/RaftManager.cc

@@ -582,6 +582,8 @@ void RaftManager::replicate_log(ReplicaRequest * request)
     {
         request->notify();
 
+        requests.remove(request->index());
+
         pthread_mutex_unlock(&mutex);
         return;
     }
@@ -593,9 +595,15 @@ void RaftManager::replicate_log(ReplicaRequest * request)
 
     for (it = next.begin(); it != next.end() && to_commit > 0; ++it)
     {
-        if ( request->index() < (int) it->second )
+        int rindex = request->index();
+
+        if ( rindex < (int) it->second )
         {
             to_commit--;
+        }
+		 else if ( rindex == (int) it->second )
+		 {
+            replica_manager.replicate(it->first);
         }
     }
 
@@ -607,6 +615,8 @@ void RaftManager::replicate_log(ReplicaRequest * request)
         request->timeout = false;
 
         commit = request->index();
+
+        requests.remove(request->index());
     }
     else
     {
@@ -615,11 +625,6 @@ void RaftManager::replicate_log(ReplicaRequest * request)
         requests.set(request->index(), request);
     }
 
-    if ( num_servers > 1 )
-    {
-        replica_manager.replicate();
-    }
-
     pthread_mutex_unlock(&mutex);
 }
 
@@ -661,7 +666,8 @@ void RaftManager::replicate_success(int follower_id)
         commit = replicated_index;
     }
         
-    if ( db_lindex > replicated_index && state == LEADER )
+    if (db_lindex > replicated_index && state == LEADER &&
+            requests.is_replicable(replicated_index + 1))
     {
         replica_manager.replicate(follower_id);
     }

src/sql/LogDB.cc

@@ -405,6 +405,12 @@ int LogDB::insert_log_record(unsigned int term, std::ostringstream& sql,
         return -1;
     }
 
+    //allocate a replication request if log record is going to be replicated
+    if ( timestamp == 0 )
+    {
+        Nebula::instance().get_raftm()->replicate_allocate(next_index);
+    }
+
     last_index = next_index;
 
     last_term  = term;