RATIS-1862 Add the parameter whether to take Snapshot when stopping t…

…o adapt to different services (#896)

ratis-server-api/src/main/java/org/apache/ratis/server/RaftServerConfigKeys.java

@@ -586,6 +586,18 @@ static void setAutoTriggerEnabled(RaftProperties properties, boolean autoTrigger
       setBoolean(properties::setBoolean, AUTO_TRIGGER_ENABLED_KEY, autoTriggerEnabled);
     }
 
+    /** whether trigger snapshot when stop raft server */
+    String TRIGGER_WHEN_STOP_ENABLED_KEY = PREFIX + ".trigger-when-stop.enabled";
+    /** by default let the state machine to trigger snapshot when stop */
+    boolean TRIGGER_WHEN_STOP_ENABLED_DEFAULT = true;
+    static boolean triggerWhenStopEnabled(RaftProperties properties) {
+      return getBoolean(properties::getBoolean,
+          TRIGGER_WHEN_STOP_ENABLED_KEY, TRIGGER_WHEN_STOP_ENABLED_DEFAULT, getDefaultLog());
+    }
+    static void setTriggerWhenStopEnabled(RaftProperties properties, boolean triggerWhenStopEnabled) {
+      setBoolean(properties::setBoolean, TRIGGER_WHEN_STOP_ENABLED_KEY, triggerWhenStopEnabled);
+    }
+
     /** The log index gap between to two snapshot creations. */
     String CREATION_GAP_KEY = PREFIX + ".creation.gap";
     long CREATION_GAP_DEFAULT = 1024;

ratis-server/src/main/java/org/apache/ratis/server/impl/StateMachineUpdater.java

@@ -72,6 +72,8 @@ enum State {
   private final RaftServerImpl server;
   private final RaftLog raftLog;
 
+  private final boolean triggerSnapshotWhenStopEnabled;
+
   private final Long autoSnapshotThreshold;
   private final boolean purgeUptoSnapshotIndex;
 
@@ -103,6 +105,7 @@ enum State {
     this.appliedIndex = new RaftLogIndex("appliedIndex", lastAppliedIndex);
     this.snapshotIndex = new RaftLogIndex("snapshotIndex", lastAppliedIndex);
 
+    this.triggerSnapshotWhenStopEnabled = RaftServerConfigKeys.Snapshot.triggerWhenStopEnabled(properties);
     final boolean autoSnapshot = RaftServerConfigKeys.Snapshot.autoTriggerEnabled(properties);
     this.autoSnapshotThreshold = autoSnapshot? RaftServerConfigKeys.Snapshot.autoTriggerThreshold(properties): null;
     final int numSnapshotFilesRetained = RaftServerConfigKeys.Snapshot.retentionFileNum(properties);
@@ -317,7 +320,7 @@ private boolean shouldTakeSnapshot() {
     if (autoSnapshotThreshold == null) {
       return false;
     } else if (shouldStop()) {
-      return getLastAppliedIndex() - snapshotIndex.get() > 0;
+      return triggerSnapshotWhenStopEnabled && getLastAppliedIndex() - snapshotIndex.get() > 0;
     }
     return state == State.RUNNING &&
         getStateMachineLastAppliedIndex() - snapshotIndex.get() >= autoSnapshotThreshold;