diff --git a/hbase-hadoop2-compat/src/main/java/org/apache/hadoop/metrics2/lib/MetricsExecutorImpl.java b/hbase-hadoop2-compat/src/main/java/org/apache/hadoop/metrics2/lib/MetricsExecutorImpl.java
index c38160974160..0a83a5e8b02d 100644
--- a/hbase-hadoop2-compat/src/main/java/org/apache/hadoop/metrics2/lib/MetricsExecutorImpl.java
+++ b/hbase-hadoop2-compat/src/main/java/org/apache/hadoop/metrics2/lib/MetricsExecutorImpl.java
@@ -48,7 +48,7 @@ public void stop() {
 
   private enum ExecutorSingleton {
     INSTANCE;
-    private final ScheduledExecutorService scheduler = new ScheduledThreadPoolExecutor(1,
+    private transient final ScheduledExecutorService scheduler = new ScheduledThreadPoolExecutor(1,
         new ThreadPoolExecutorThreadFactory("HBase-Metrics2-"));
   }
 
diff --git a/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/HRegion.java b/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/HRegion.java
index d667786c97e0..f7abe2ac3c91 100644
--- a/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/HRegion.java
+++ b/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/HRegion.java
@@ -7812,11 +7812,15 @@ public Result append(Append mutate, long nonceGroup, long nonce) throws IOExcept
         for (Map.Entry<Store, List<Cell>> entry : removedCellsForMemStore.entrySet()) {
           Store currStore = entry.getKey();
           for (Cell cell: entry.getValue()) {
-            CellUtil.setSequenceId(cell, walKey.getWriteEntry().getWriteNumber());
+            if (we != null) {
+              CellUtil.setSequenceId(cell, we.getWriteNumber());
+            }
             currStore.add(cell);
           }
         }
-        if (we != null) mvcc.complete(we);
+        if (we != null) {
+          mvcc.complete(we);
+        }
       } else if (we != null) {
         mvcc.completeAndWait(we);
       }
@@ -8042,6 +8046,7 @@ private Result doIncrement(Increment increment, long nonceGroup, long nonce) thr
         rowLock.release();
       }
       // if the wal sync was unsuccessful, remove keys from memstore
+      WriteEntry we = walKey != null ? walKey.getWriteEntry() : null;
       if (doRollBackMemstore) {
         for (Map.Entry<Store, List<Cell>> entry : forMemStore.entrySet()) {
           rollbackMemstore(entry.getKey(), entry.getValue());
@@ -8049,13 +8054,19 @@ private Result doIncrement(Increment increment, long nonceGroup, long nonce) thr
         for (Map.Entry<Store, List<Cell>> entry : removedCellsForMemStore.entrySet()) {
           Store currStore = entry.getKey();
           for (Cell cell : entry.getValue()) {
-            CellUtil.setSequenceId(cell, walKey.getWriteEntry().getWriteNumber());
+            if (we != null) {
+              CellUtil.setSequenceId(cell, we.getWriteNumber());
+            }
             currStore.add(cell);
           }
         }
-        if (walKey != null) mvcc.complete(walKey.getWriteEntry());
+        if (we != null) {
+          mvcc.complete(we);
+        }
       } else {
-        if (walKey != null) mvcc.completeAndWait(walKey.getWriteEntry());
+        if (we != null) {
+          mvcc.completeAndWait(we);
+        }
       }
     }
 
diff --git a/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/HStore.java b/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/HStore.java
index 08dc3f853827..764099f270e2 100644
--- a/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/HStore.java
+++ b/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/HStore.java
@@ -2806,10 +2806,14 @@ private void removeCompactedfiles(Collection<StoreFile> compactedfiles)
             // Just close and return
             filesToRemove.add(file);
           } else {
-            LOG.info("Can't archive compacted file " + file.getPath()
+            if (r != null) {
+              LOG.info("Can't archive compacted file " + file.getPath()
                 + " because of either isCompactedAway=" + r.isCompactedAway()
                 + " or file has reference, isReferencedInReads=" + r.isReferencedInReads()
                 + ", refCount=" + r.getRefCount() + ", skipping for now.");
+            } else {
+              LOG.info("Can't archive compacted file " + file.getPath() + ", skipping for now.");
+            }
           }
         } catch (Exception e) {
           LOG.error(
diff --git a/hbase-server/src/main/java/org/apache/hadoop/hbase/tool/Canary.java b/hbase-server/src/main/java/org/apache/hadoop/hbase/tool/Canary.java
index c0655d8d4e8e..7c17db9d643b 100644
--- a/hbase-server/src/main/java/org/apache/hadoop/hbase/tool/Canary.java
+++ b/hbase-server/src/main/java/org/apache/hadoop/hbase/tool/Canary.java
@@ -35,6 +35,7 @@
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
+import java.util.Map.Entry;
 import java.util.Random;
 import java.util.Set;
 import java.util.TreeSet;
@@ -1089,7 +1090,8 @@ public void run() {
             }
           }
           Map<String, AtomicLong> actualReadTableLatency = regionSink.getReadLatencyMap();
-          for (String tableName : this.configuredReadTableTimeouts.keySet()) {
+          for (Entry<String, Long> entry : this.configuredReadTableTimeouts.entrySet()) {
+            String tableName = entry.getKey();
             if (actualReadTableLatency.containsKey(tableName)) {
               Long actual = actualReadTableLatency.get(tableName).longValue();
               Long configured = this.configuredReadTableTimeouts.get(tableName);