YARN-7024: Fix issues on recovery in LevelDB store. Contributed by Jonathan Hung

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/capacity/conf/InMemoryConfigurationStore.java

@@ -79,7 +79,7 @@ public class InMemoryConfigurationStore implements YarnConfigurationStore {
 
   @Override
   public synchronized List<LogMutation> getPendingMutations() {
-    return pendingMutations;
+    return new LinkedList<>(pendingMutations);
   }
 
   @Override

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/capacity/conf/LeveldbConfigurationStore.java

@@ -65,6 +65,7 @@ public class LeveldbConfigurationStore implements YarnConfigurationStore {
   private static final String LOG_COMMITTED_TXN = "committedTxn";
 
   private DB db;
+  // Txnid for the last transaction logged to the store.
   private long txnId = 0;
   private long minTxn = 0;
   private long maxLogs;
@@ -92,6 +93,7 @@ public class LeveldbConfigurationStore implements YarnConfigurationStore {
           break;
         }
         pendingMutations.add(deserLogMutation(entry.getValue()));
+        txnId++;
       }
       // Get the earliest txnId stored in logs
       itr.seekToFirst();
@@ -278,7 +280,7 @@ public class LeveldbConfigurationStore implements YarnConfigurationStore {
 
   @Override
   public List<LogMutation> getPendingMutations() {
-    return pendingMutations;
+    return new LinkedList<>(pendingMutations);
   }
 
   @Override