Enhance code documentation and add TODOs

[controller.git] / opendaylight / md-sal / sal-akka-raft / src / main / java / org / opendaylight / controller / cluster / raft / behaviors / Leader.java

diff --git a/opendaylight/md-sal/sal-akka-raft/src/main/java/org/opendaylight/controller/cluster/raft/behaviors/Leader.java b/opendaylight/md-sal/sal-akka-raft/src/main/java/org/opendaylight/controller/cluster/raft/behaviors/Leader.java
index a9882a664767ad726c651611c6cff8ac078f6d1a..fb8be8b891a315b420c6778f1691ba4712a069d7 100644 (file)
--- a/opendaylight/md-sal/sal-akka-raft/src/main/java/org/opendaylight/controller/cluster/raft/behaviors/Leader.java
+++ b/opendaylight/md-sal/sal-akka-raft/src/main/java/org/opendaylight/controller/cluster/raft/behaviors/Leader.java
@@ -137,6 +137,13 @@ public class Leader extends AbstractRaftActorBehavior {
             followerLogInformation
                 .setNextIndex(appendEntriesReply.getLogLastIndex() + 1);
         } else {
+
+            // TODO: When we find that the follower is out of sync with the
+            // Leader we simply decrement that followers next index by 1.
+            // Would it be possible to do better than this? The RAFT spec
+            // does not explicitly deal with it but may be something for us to
+            // think about
+
             followerLogInformation.decrNextIndex();
         }
 
@@ -215,7 +222,6 @@ public class Leader extends AbstractRaftActorBehavior {
             } else if (message instanceof Replicate) {
                 replicate((Replicate) message);
             } else if (message instanceof InstallSnapshotReply){
-                // FIXME : Should I be checking the term here too?
                 handleInstallSnapshotReply(
                     (InstallSnapshotReply) message);
             }
@@ -281,6 +287,12 @@ public class Leader extends AbstractRaftActorBehavior {
             List<ReplicatedLogEntry> entries = Collections.emptyList();
 
             if(context.getReplicatedLog().isPresent(nextIndex)){
+                // TODO: Instead of sending all entries from nextIndex
+                // only send a fixed number of entries to each follower
+                // This is to avoid the situation where there are a lot of
+                // entries to install for a fresh follower or to a follower
+                // that has fallen too far behind with the log but yet is not
+                // eligible to receive a snapshot
                 entries =
                     context.getReplicatedLog().getFrom(nextIndex);
             }
@@ -295,6 +307,11 @@ public class Leader extends AbstractRaftActorBehavior {
         }
     }
 
+    /**
+     * An installSnapshot is scheduled at a interval that is a multiple of
+     * a HEARTBEAT_INTERVAL. This is to avoid the need to check for installing
+     * snapshots at every heartbeat.
+     */
     private void installSnapshotIfNeeded(){
         for (String followerId : followerToActor.keySet()) {
             ActorSelection followerActor =