From b6756b39c2ff5675f96a6e82dc4d68ec437f01c4 Mon Sep 17 00:00:00 2001
From: Elliott Clark <eclark@apache.org>
Date: Mon, 6 Apr 2015 10:22:32 -0700
Subject: [PATCH] HBASE-13412 Region split decisions should have jitter

---
 .../ConstantSizeRegionSplitPolicy.java        |  6 ++++++
 .../regionserver/TestRegionSplitPolicy.java   | 19 +++++++++++++------
 2 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/ConstantSizeRegionSplitPolicy.java b/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/ConstantSizeRegionSplitPolicy.java
index 2459ae6a4e3..66ef712519c 100644
--- a/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/ConstantSizeRegionSplitPolicy.java
+++ b/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/ConstantSizeRegionSplitPolicy.java
@@ -23,6 +23,8 @@ import org.apache.hadoop.hbase.HBaseInterfaceAudience;
 import org.apache.hadoop.hbase.HConstants;
 import org.apache.hadoop.hbase.HTableDescriptor;
 
+import java.util.Random;
+
 /**
  * A {@link RegionSplitPolicy} implementation which splits a region
  * as soon as any of its store files exceeds a maximum configurable
@@ -34,6 +36,8 @@ import org.apache.hadoop.hbase.HTableDescriptor;
  */
 @InterfaceAudience.LimitedPrivate(HBaseInterfaceAudience.CONFIG)
 public class ConstantSizeRegionSplitPolicy extends RegionSplitPolicy {
+  private static final Random RANDOM = new Random();
+
   private long desiredMaxFileSize;
 
   @Override
@@ -48,6 +52,8 @@ public class ConstantSizeRegionSplitPolicy extends RegionSplitPolicy {
       this.desiredMaxFileSize = conf.getLong(HConstants.HREGION_MAX_FILESIZE,
         HConstants.DEFAULT_MAX_FILE_SIZE);
     }
+    double jitter = conf.getDouble("hbase.hregion.max.filesize.jitter", 0.25D);
+    this.desiredMaxFileSize += (long)(desiredMaxFileSize * (RANDOM.nextFloat() - 0.5D) * jitter);
   }
 
   @Override
diff --git a/hbase-server/src/test/java/org/apache/hadoop/hbase/regionserver/TestRegionSplitPolicy.java b/hbase-server/src/test/java/org/apache/hadoop/hbase/regionserver/TestRegionSplitPolicy.java
index 6a234bbf870..9cb2b4454f5 100644
--- a/hbase-server/src/test/java/org/apache/hadoop/hbase/regionserver/TestRegionSplitPolicy.java
+++ b/hbase-server/src/test/java/org/apache/hadoop/hbase/regionserver/TestRegionSplitPolicy.java
@@ -110,14 +110,21 @@ public class TestRegionSplitPolicy {
     // now be no longer be splittable since split size has gone up.
     regions.add(mockRegion);
     assertFalse(policy.shouldSplit());
-    // Quadruple (2 squared) the store size and make sure its just over; verify it'll split
-    Mockito.doReturn((flushSize * 2 * 2 * 2) + 1).when(mockStore).getSize();
+    // make sure its just over; verify it'll split
+    Mockito.doReturn((long)(maxSplitSize * 1.025 + 1)).when(mockStore).getSize();
     assertTrue(policy.shouldSplit());
 
     // Finally assert that even if loads of regions, we'll split at max size
-    assertEquals(maxSplitSize, policy.getSizeToCheck(1000));
+    assertWithinJitter(maxSplitSize, policy.getSizeToCheck(1000));
     // Assert same is true if count of regions is zero.
-    assertEquals(maxSplitSize, policy.getSizeToCheck(0));
+    assertWithinJitter(maxSplitSize, policy.getSizeToCheck(0));
+  }
+
+  private void assertWithinJitter(long maxSplitSize, long sizeToCheck) {
+    assertTrue("Size greater than lower bound of jitter",
+        (long)(maxSplitSize * 0.75) <= sizeToCheck);
+    assertTrue("Size less than upper bound of jitter",
+        (long)(maxSplitSize * 1.25) >= sizeToCheck);
   }
 
   @Test
@@ -129,13 +136,13 @@ public class TestRegionSplitPolicy {
     ConstantSizeRegionSplitPolicy policy =
         (ConstantSizeRegionSplitPolicy)RegionSplitPolicy.create(
             mockRegion, conf);
-    assertEquals(1234L, policy.getDesiredMaxFileSize());
+    assertWithinJitter(1234L, policy.getDesiredMaxFileSize());
 
     // If specified in HTD, should use that
     htd.setMaxFileSize(9999L);
     policy = (ConstantSizeRegionSplitPolicy)RegionSplitPolicy.create(
         mockRegion, conf);
-    assertEquals(9999L, policy.getDesiredMaxFileSize());
+    assertWithinJitter(9999L, policy.getDesiredMaxFileSize());
   }
 
   /**