YARN-8151. Yarn RM Epoch should wrap around. Contributed by Young Chen.

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-api/src/main/java/org/apache/hadoop/yarn/conf/YarnConfiguration.java

@@ -188,6 +188,10 @@ public class YarnConfiguration extends Configuration {
   public static final String RM_EPOCH = RM_PREFIX + "epoch";
   public static final long DEFAULT_RM_EPOCH = 0L;
 
+  /** The epoch range before wrap around. 0 disables wrap around*/
+  public static final String RM_EPOCH_RANGE = RM_EPOCH + ".range";
+  public static final long DEFAULT_RM_EPOCH_RANGE = 0;
+
   /** The address of the applications manager interface in the RM.*/
   public static final String RM_ADDRESS = 
     RM_PREFIX + "address";

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-common/src/main/resources/yarn-default.xml

@@ -676,6 +676,13 @@
     <!--value>yarn-cluster</value-->
   </property>
 
+  <property>
+    <description>The range of values above base epoch that the RM will use before
+      wrapping around</description>
+    <name>yarn.resourcemanager.epoch.range</name>
+    <value>0</value>
+  </property>
+
   <property>
     <description>The list of RM nodes in the cluster when HA is
       enabled. See description of yarn.resourcemanager.ha

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/recovery/FileSystemRMStateStore.java

@@ -205,12 +205,12 @@ public class FileSystemRMStateStore extends RMStateStore {
       Epoch epoch = new EpochPBImpl(EpochProto.parseFrom(data));
       currentEpoch = epoch.getEpoch();
       // increment epoch and store it
-      byte[] storeData = Epoch.newInstance(currentEpoch + 1).getProto()
+      byte[] storeData = Epoch.newInstance(nextEpoch(currentEpoch)).getProto()
           .toByteArray();
       updateFile(epochNodePath, storeData, false);
     } else {
       // initialize epoch file with 1 for the next time.
-      byte[] storeData = Epoch.newInstance(currentEpoch + 1).getProto()
+      byte[] storeData = Epoch.newInstance(nextEpoch(currentEpoch)).getProto()
           .toByteArray();
       writeFileWithRetries(epochNodePath, storeData, false);
     }

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/recovery/LeveldbRMStateStore.java

@@ -259,7 +259,7 @@ public class LeveldbRMStateStore extends RMStateStore {
       if (data != null) {
         currentEpoch = EpochProto.parseFrom(data).getEpoch();
       }
-      EpochProto proto = Epoch.newInstance(currentEpoch + 1).getProto();
+      EpochProto proto = Epoch.newInstance(nextEpoch(currentEpoch)).getProto();
       db.put(dbKeyBytes, proto.toByteArray());
     } catch (DBException e) {
       throw new IOException(e);

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/recovery/MemoryRMStateStore.java

@@ -59,7 +59,7 @@ public class MemoryRMStateStore extends RMStateStore {
   @Override
   public synchronized long getAndIncrementEpoch() throws Exception {
     long currentEpoch = epoch;
-    epoch = epoch + 1;
+    epoch = nextEpoch(epoch);
     return currentEpoch;
   }
 

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/recovery/RMStateStore.java

@@ -104,6 +104,7 @@ public abstract class RMStateStore extends AbstractService {
   protected static final String VERSION_NODE = "RMVersionNode";
   protected static final String EPOCH_NODE = "EpochNode";
   protected long baseEpoch;
+  private long epochRange;
   protected ResourceManager resourceManager;
   private final ReadLock readLock;
   private final WriteLock writeLock;
@@ -732,6 +733,8 @@ public abstract class RMStateStore extends AbstractService {
     // read the base epoch value from conf
     baseEpoch = conf.getLong(YarnConfiguration.RM_EPOCH,
         YarnConfiguration.DEFAULT_RM_EPOCH);
+    epochRange = conf.getLong(YarnConfiguration.RM_EPOCH_RANGE,
+        YarnConfiguration.DEFAULT_RM_EPOCH_RANGE);
     initInternal(conf);
   }
 
@@ -819,6 +822,19 @@ public abstract class RMStateStore extends AbstractService {
    */
   public abstract long getAndIncrementEpoch() throws Exception;
 
+  /**
+   * Compute the next epoch value by incrementing by one.
+   * Wraps around if the epoch range is exceeded so that
+   * when federation is enabled epoch collisions can be avoided.
+   */
+  protected long nextEpoch(long epoch){
+    long epochVal = epoch - baseEpoch + 1;
+    if (epochRange > 0) {
+      epochVal %= epochRange;
+    }
+    return  epochVal + baseEpoch;
+  }
+
   /**
    * Blocking API
    * The derived class must recover state from the store and return a new 

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/recovery/ZKRMStateStore.java

@@ -491,13 +491,13 @@ public class ZKRMStateStore extends RMStateStore {
       Epoch epoch = new EpochPBImpl(EpochProto.parseFrom(data));
       currentEpoch = epoch.getEpoch();
       // increment epoch and store it
-      byte[] storeData = Epoch.newInstance(currentEpoch + 1).getProto()
+      byte[] storeData = Epoch.newInstance(nextEpoch(currentEpoch)).getProto()
           .toByteArray();
       zkManager.safeSetData(epochNodePath, storeData, -1, zkAcl,
           fencingNodePath);
     } else {
       // initialize epoch node with 1 for the next time.
-      byte[] storeData = Epoch.newInstance(currentEpoch + 1).getProto()
+      byte[] storeData = Epoch.newInstance(nextEpoch(currentEpoch)).getProto()
           .toByteArray();
       zkManager.safeCreate(epochNodePath, storeData, zkAcl,
           CreateMode.PERSISTENT, zkAcl, fencingNodePath);

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/recovery/RMStateStoreTestBase.java

@@ -94,6 +94,8 @@ public class RMStateStoreTestBase {
 
   protected final long epoch = 10L;
 
+  private final long epochRange = 10L;
+
   static class TestDispatcher implements Dispatcher, EventHandler<Event> {
 
     ApplicationAttemptId attemptId;
@@ -141,6 +143,10 @@ public class RMStateStoreTestBase {
     boolean attemptExists(RMAppAttempt attempt) throws Exception;
   }
 
+  public long getEpochRange() {
+    return epochRange;
+  }
+
   void waitNotify(TestDispatcher dispatcher) {
     long startTime = System.currentTimeMillis();
     while(!dispatcher.notified) {
@@ -576,6 +582,14 @@ public class RMStateStoreTestBase {
     
     long thirdTimeEpoch = store.getAndIncrementEpoch();
     Assert.assertEquals(epoch + 2, thirdTimeEpoch);
+
+    for (int i = 0; i < epochRange; ++i) {
+      store.getAndIncrementEpoch();
+    }
+    long wrappedEpoch = store.getAndIncrementEpoch();
+    // Epoch should have wrapped around and then incremented once for a total
+    // of + 3
+    Assert.assertEquals(epoch + 3, wrappedEpoch);
   }
 
   public void testAppDeletion(RMStateStoreHelper stateStoreHelper)

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/recovery/TestFSRMStateStore.java

@@ -118,6 +118,7 @@ public class TestFSRMStateStore extends RMStateStoreTestBase {
       conf.setLong(YarnConfiguration.FS_RM_STATE_STORE_RETRY_INTERVAL_MS,
               900L);
       conf.setLong(YarnConfiguration.RM_EPOCH, epoch);
+      conf.setLong(YarnConfiguration.RM_EPOCH_RANGE, getEpochRange());
       if (adminCheckEnable) {
         conf.setBoolean(
           YarnConfiguration.YARN_INTERMEDIATE_DATA_ENCRYPTION, true);

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/recovery/TestLeveldbRMStateStore.java

@@ -83,6 +83,7 @@ public class TestLeveldbRMStateStore extends RMStateStoreTestBase {
   @Test(timeout = 60000)
   public void testEpoch() throws Exception {
     conf.setLong(YarnConfiguration.RM_EPOCH, epoch);
+    conf.setLong(YarnConfiguration.RM_EPOCH_RANGE, getEpochRange());
     LeveldbStateStoreTester tester = new LeveldbStateStoreTester();
     testEpoch(tester);
   }

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/recovery/TestZKRMStateStore.java

@@ -210,6 +210,7 @@ public class TestZKRMStateStore extends RMStateStoreTestBase {
           curatorTestingServer.getConnectString());
       conf.set(YarnConfiguration.ZK_RM_STATE_STORE_PARENT_PATH, workingZnode);
       conf.setLong(YarnConfiguration.RM_EPOCH, epoch);
+      conf.setLong(YarnConfiguration.RM_EPOCH_RANGE, getEpochRange());
       this.store = new TestZKRMStateStoreInternal(conf, workingZnode);
       return this.store;
     }