HBASE-20914 Trim Master memory usage

Add (weak reference) interning of ServerNames.

Correct Balancer regions x racks matrix.

Make smaller defaults when creating ArrayDeques.

hbase-common/src/main/java/org/apache/hadoop/hbase/ServerName.java

@@ -27,9 +27,11 @@ import java.util.regex.Pattern;
 import org.apache.hadoop.hbase.net.Address;
 import org.apache.hadoop.hbase.util.Addressing;
 import org.apache.hadoop.hbase.util.Bytes;
+import org.apache.hbase.thirdparty.com.google.common.collect.Interner;
+import org.apache.hbase.thirdparty.com.google.common.collect.Interners;
+import org.apache.hbase.thirdparty.com.google.common.net.InetAddresses;
 import org.apache.yetus.audience.InterfaceAudience;
 
-import org.apache.hbase.thirdparty.com.google.common.net.InetAddresses;
 
 
 /**
@@ -99,6 +101,13 @@ public class ServerName implements Comparable<ServerName>, Serializable {
   private byte [] bytes;
   public static final List<ServerName> EMPTY_SERVER_LIST = new ArrayList<>(0);
 
+  /**
+   * Intern ServerNames. The Set of ServerNames is mostly-fixed changing slowly as Servers
+   * restart. Rather than create a new instance everytime, try and return existing instance
+   * if there is one.
+   */
+  private static final Interner<ServerName> INTERN_POOL = Interners.newWeakInterner();
+
   protected ServerName(final String hostname, final int port, final long startcode) {
     this(Address.fromParts(hostname, port), startcode);
   }
@@ -176,7 +185,7 @@ public class ServerName implements Comparable<ServerName>, Serializable {
    * a shared immutable object as an internal optimization.
    */
   public static ServerName valueOf(final String hostname, final int port, final long startcode) {
-    return new ServerName(hostname, port, startcode);
+    return INTERN_POOL.intern(new ServerName(hostname, port, startcode));
   }
 
   /**
@@ -185,7 +194,7 @@ public class ServerName implements Comparable<ServerName>, Serializable {
    * a shared immutable object as an internal optimization.
    */
   public static ServerName valueOf(final String serverName) {
-    return new ServerName(serverName);
+    return INTERN_POOL.intern(new ServerName(serverName));
   }
 
   /**
@@ -194,7 +203,7 @@ public class ServerName implements Comparable<ServerName>, Serializable {
    * a shared immutable object as an internal optimization.
    */
   public static ServerName valueOf(final String hostAndPort, final long startCode) {
-    return new ServerName(hostAndPort, startCode);
+    return INTERN_POOL.intern(new ServerName(hostAndPort, startCode));
   }
 
   @Override

hbase-procedure/src/main/java/org/apache/hadoop/hbase/procedure2/ProcedureDeque.java

@@ -31,4 +31,8 @@ import java.util.ArrayDeque;
  */
 @InterfaceAudience.Private
 public class ProcedureDeque extends ArrayDeque<Procedure> {
+  public ProcedureDeque() {
+    // Default is 16 for a list that is rarely used; elements will resize if too small.
+    super(2);
+  }
 }

hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/BaseLoadBalancer.java

@@ -566,7 +566,7 @@ public abstract class BaseLoadBalancer implements LoadBalancer {
      * and rack have the highest locality for region
      */
     private void computeCachedLocalities() {
-      rackLocalities = new float[numRegions][numServers];
+      rackLocalities = new float[numRegions][numRacks];
       regionsToMostLocalEntities = new int[LocalityType.values().length][numRegions];
 
       // Compute localities and find most local server per region

hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/StochasticLoadBalancer.java

@@ -532,8 +532,7 @@ public class StochasticLoadBalancer extends BaseLoadBalancer {
       sm.getRegionMetrics().forEach((byte[] regionName, RegionMetrics rm) -> {
         Deque<BalancerRegionLoad> rLoads = oldLoads.get(Bytes.toString(regionName));
         if (rLoads == null) {
-          // There was nothing there
-          rLoads = new ArrayDeque<>();
+          rLoads = new ArrayDeque<>(numRegionLoadsToRemember + 1);
         } else if (rLoads.size() >= numRegionLoadsToRemember) {
           rLoads.remove();
         }

hbase-server/src/test/java/org/apache/hadoop/hbase/TestServerName.java

@@ -20,16 +20,19 @@ package org.apache.hadoop.hbase;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotSame;
+import static org.junit.Assert.assertSame;
 import static org.junit.Assert.assertTrue;
 
 import java.util.HashSet;
 import java.util.Set;
 import java.util.regex.Pattern;
+
 import org.apache.hadoop.hbase.testclassification.MiscTests;
 import org.apache.hadoop.hbase.testclassification.SmallTests;
 import org.apache.hadoop.hbase.util.Addressing;
 import org.apache.hadoop.hbase.util.Bytes;
 import org.junit.ClassRule;
+import org.junit.Ignore;
 import org.junit.Test;
 import org.junit.experimental.categories.Category;
 
@@ -86,7 +89,8 @@ public class TestServerName {
     ServerName.parseServerName("192.168.1.199:58102");
   }
 
-  @Test public void testParseOfBytes() {
+  @Test
+  public void testParseOfBytes() {
     final String snStr = "www.EXAMPLE.org,1234,5678";
     ServerName sn = ServerName.valueOf(snStr);
     byte[] versionedBytes = sn.getVersionedBytes();
@@ -132,5 +136,19 @@ public class TestServerName {
     assertTrue(upper.equals(lower));
     assertTrue(ServerName.isSameAddress(lower, upper));
   }
+
+  @Test
+  public void testInterning() {
+    ServerName sn1 = ServerName.valueOf("www.example.org", 1234, 5671);
+    assertSame(sn1, ServerName.valueOf("www.example.org", 1234, 5671));
+  }
+
+  @Ignore // Enable and let fun for hours to make sure weak references working fine.
+  @Test
+  public void testInterningDoesWeakReferences() {
+    for (int i = 0; i < Integer.MAX_VALUE; i++) {
+      ServerName.valueOf("www.example.org", 1234, i++);
+    }
+  }
 }