BUG 2185: Expand the scope of sync status to cover a slow follower

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

diff --git a/opendaylight/md-sal/sal-akka-raft/src/main/java/org/opendaylight/controller/cluster/raft/behaviors/SyncStatusTracker.java b/opendaylight/md-sal/sal-akka-raft/src/main/java/org/opendaylight/controller/cluster/raft/behaviors/SyncStatusTracker.java
new file mode 100644 (file)
index 0000000..85622a5
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+++ b/opendaylight/md-sal/sal-akka-raft/src/main/java/org/opendaylight/controller/cluster/raft/behaviors/SyncStatusTracker.java
@@ -0,0 +1,71 @@
+/*
+ * Copyright (c) 2015 Cisco Systems, Inc. and others.  All rights reserved.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v1.0 which accompanies this distribution,
+ * and is available at http://www.eclipse.org/legal/epl-v10.html
+ */
+
+package org.opendaylight.controller.cluster.raft.behaviors;
+
+import akka.actor.ActorRef;
+import com.google.common.base.Preconditions;
+import org.opendaylight.controller.cluster.raft.base.messages.FollowerInitialSyncUpStatus;
+
+/**
+ * The SyncStatusTracker tracks if a Follower is in sync with any given Leader or not
+ * When an update is received from the Leader and the update happens to be the first update
+ * from that Leader then the SyncStatusTracker will not mark the Follower as not in-sync till the
+ * Followers commitIndex matches the commitIndex that the Leader sent in it's very first update.
+ * Subsequently when an update is received the tracker will consider the Follower to be out of
+ * sync if it is behind by 'syncThreshold' commits.
+ */
+public class SyncStatusTracker {
+
+    private static final boolean IN_SYNC = true;
+    private static final boolean NOT_IN_SYNC = false;
+    private static final boolean FORCE_STATUS_CHANGE = true;
+
+    private final String id;
+    private String syncedLeaderId = null;
+    private final ActorRef actor;
+    private final int syncThreshold;
+    private boolean syncStatus = false;
+    private long minimumExpectedIndex = -2L;
+
+    public SyncStatusTracker(ActorRef actor, String id, int syncThreshold) {
+        this.actor = Preconditions.checkNotNull(actor, "actor should not be null");
+        this.id = Preconditions.checkNotNull(id, "id should not be null");
+        Preconditions.checkArgument(syncThreshold >= 0, "syncThreshold should be greater than or equal to 0");
+        this.syncThreshold = syncThreshold;
+    }
+
+    public void update(String leaderId, long leaderCommit, long commitIndex){
+        leaderId = Preconditions.checkNotNull(leaderId, "leaderId should not be null");
+
+        if(!leaderId.equals(syncedLeaderId)){
+            minimumExpectedIndex = leaderCommit;
+            changeSyncStatus(NOT_IN_SYNC, FORCE_STATUS_CHANGE);
+            syncedLeaderId = leaderId;
+            return;
+        }
+
+        if((leaderCommit - commitIndex) > syncThreshold){
+            changeSyncStatus(NOT_IN_SYNC);
+        } else if((leaderCommit - commitIndex) <= syncThreshold && commitIndex >= minimumExpectedIndex) {
+            changeSyncStatus(IN_SYNC);
+        }
+    }
+
+    private void changeSyncStatus(boolean newSyncStatus){
+        changeSyncStatus(newSyncStatus, !FORCE_STATUS_CHANGE);
+    }
+
+    private void changeSyncStatus(boolean newSyncStatus, boolean forceStatusChange){
+        if(syncStatus == newSyncStatus && !forceStatusChange){
+            return;
+        }
+        actor.tell(new FollowerInitialSyncUpStatus(newSyncStatus, id), ActorRef.noSender());
+        syncStatus = newSyncStatus;
+    }
+}
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