HBASE-12655 WALPerformanceEvaluation should only add stat gathering listener once per WAL.

hbase-server/src/main/java/org/apache/hadoop/hbase/wal/WAL.java

@@ -41,6 +41,9 @@ import org.apache.hadoop.hbase.regionserver.wal.WALEdit;
 /**
  * A Write Ahead Log (WAL) provides service for reading, writing waledits. This interface provides
  * APIs for WAL users (such as RegionServer) to use the WAL (do append, sync, etc).
+ *
+ * Note that some internals, such as log rolling and performance evaluation tools, will use
+ * WAL.equals to determine if they have already seen a given WAL.
  */
 @InterfaceAudience.Private
 @InterfaceStability.Evolving

hbase-server/src/test/java/org/apache/hadoop/hbase/wal/TestDefaultWALProvider.java

@@ -19,9 +19,14 @@
 package org.apache.hadoop.hbase.wal;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
 
 import java.io.IOException;
+import java.util.HashSet;
+import java.util.Random;
+import java.util.Set;
 import java.util.concurrent.atomic.AtomicLong;
 
 import org.apache.commons.logging.Log;
@@ -329,4 +334,26 @@ public class TestDefaultWALProvider {
         new String [] {"-threads", "3", "-verify", "-noclosefs", "-iterations", "3000"});
     assertEquals(0, errCode);
   }
+
+  /**
+   * Ensure that we can use Set.add to deduplicate WALs
+   */
+  @Test
+  public void setMembershipDedups() throws IOException {
+    final Configuration localConf = new Configuration(conf);
+    localConf.set(WALFactory.WAL_PROVIDER, DefaultWALProvider.class.getName());
+    final WALFactory wals = new WALFactory(localConf, null, currentTest.getMethodName());
+    try {
+      final Set<WAL> seen = new HashSet<WAL>(1);
+      final Random random = new Random();
+      assertTrue("first attempt to add WAL from default provider should work.",
+          seen.add(wals.getWAL(Bytes.toBytes(random.nextInt()))));
+      for (int i = 0; i < 1000; i++) {
+        assertFalse("default wal provider is only supposed to return a single wal, which should " +
+            "compare as .equals itself.", seen.add(wals.getWAL(Bytes.toBytes(random.nextInt()))));
+      }
+    } finally {
+      wals.close();
+    }
+  }
 }

hbase-server/src/test/java/org/apache/hadoop/hbase/wal/WALPerformanceEvaluation.java

@@ -21,9 +21,11 @@ package org.apache.hadoop.hbase.wal;
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Random;
+import java.util.Set;
 import java.util.UUID;
 import java.util.concurrent.TimeUnit;
 
@@ -460,12 +462,16 @@ public final class WALPerformanceEvaluation extends Configured implements Tool {
     System.exit(1);
   }
 
+  private final Set<WAL> walsListenedTo = new HashSet<WAL>();
+
   private HRegion openRegion(final FileSystem fs, final Path dir, final HTableDescriptor htd,
       final WALFactory wals, final long whenToRoll) throws IOException {
     // Initialize HRegion
     HRegionInfo regionInfo = new HRegionInfo(htd.getTableName());
     // Initialize WAL
     final WAL wal = wals.getWAL(regionInfo.getEncodedNameAsBytes());
+    // If we haven't already, attach a listener to this wal to handle rolls and metrics.
+    if (walsListenedTo.add(wal)) {
       wal.registerWALActionsListener(new WALActionsListener.Base() {
         private int appends = 0;
 
@@ -497,6 +503,7 @@ public final class WALPerformanceEvaluation extends Configured implements Tool {
         }
       });
       wal.rollWriter();
+    }
      
     return HRegion.createHRegion(regionInfo, dir, getConf(), htd, wal);
   }