From 5356ca07dd4077650c589010c3c0330396a05867 Mon Sep 17 00:00:00 2001
From: Alan Protasio <alanprot@gmail.com>
Date: Wed, 19 Sep 2018 12:20:59 -0700
Subject: [PATCH] AMQ-7055 - Optimization on SequenceSet to prevent iterating
 through the whole set when a value bigger than the last value is added

---
 .../store/kahadb/disk/util/Sequence.java      |  4 +++
 .../store/kahadb/disk/util/SequenceSet.java   |  7 +++++
 .../kahadb/disk/util/SequenceSetTest.java     | 31 +++++++++++++++++++
 3 files changed, 42 insertions(+)

diff --git a/activemq-kahadb-store/src/main/java/org/apache/activemq/store/kahadb/disk/util/Sequence.java b/activemq-kahadb-store/src/main/java/org/apache/activemq/store/kahadb/disk/util/Sequence.java
index f52931bd254..25e594b1df6 100644
--- a/activemq-kahadb-store/src/main/java/org/apache/activemq/store/kahadb/disk/util/Sequence.java
+++ b/activemq-kahadb-store/src/main/java/org/apache/activemq/store/kahadb/disk/util/Sequence.java
@@ -38,6 +38,10 @@ public boolean isAdjacentToLast(long value) {
         return last + 1 == value;
     }
 
+    public boolean isBiggerButNotAdjacentToLast(long value) {
+        return last + 1 < value;
+    }
+
     public boolean isAdjacentToFirst(long value) {
         return first - 1 == value;
     }
diff --git a/activemq-kahadb-store/src/main/java/org/apache/activemq/store/kahadb/disk/util/SequenceSet.java b/activemq-kahadb-store/src/main/java/org/apache/activemq/store/kahadb/disk/util/SequenceSet.java
index 2946a223c2e..fac831bf706 100644
--- a/activemq-kahadb-store/src/main/java/org/apache/activemq/store/kahadb/disk/util/SequenceSet.java
+++ b/activemq-kahadb-store/src/main/java/org/apache/activemq/store/kahadb/disk/util/SequenceSet.java
@@ -114,6 +114,13 @@ public boolean add(long value) {
             return true;
         }
 
+        // check if the value is greater than the bigger sequence value and if it's not adjacent to it
+        // in this case, we are sure that the value should be add to the tail of the sequence.
+        if (sequence.isBiggerButNotAdjacentToLast(value)) {
+            addLast(new Sequence(value));
+            return true;
+        }
+
         sequence = getHead();
         while (sequence != null) {
 
diff --git a/activemq-kahadb-store/src/test/java/org/apache/activemq/store/kahadb/disk/util/SequenceSetTest.java b/activemq-kahadb-store/src/test/java/org/apache/activemq/store/kahadb/disk/util/SequenceSetTest.java
index 272077a7992..a25b4e72aba 100644
--- a/activemq-kahadb-store/src/test/java/org/apache/activemq/store/kahadb/disk/util/SequenceSetTest.java
+++ b/activemq-kahadb-store/src/test/java/org/apache/activemq/store/kahadb/disk/util/SequenceSetTest.java
@@ -85,6 +85,37 @@ public void testContains() {
         assertFalse(set.contains(11));
     }
 
+    @Test
+    public void testAddValuesToTail() {
+        SequenceSet set = new SequenceSet();
+        set.add(new Sequence(0, 10));
+        set.add(new Sequence(21, 42));
+        set.add(new Sequence(142, 512));
+
+        set.add(513);
+
+        for (int i = 600; i < 650; i++) {
+            set.add(i);
+        }
+
+        for (int i = 0; i < 10; i++) {
+            set.add(i * 100);
+        }
+
+        assertTrue(set.contains(0));
+        assertTrue(set.contains(25));
+
+        assertTrue(set.contains(513));
+        assertTrue(!set.contains(514));
+        assertFalse(set.contains(599));
+        assertTrue(set.contains(625));
+        assertFalse(set.contains(651));
+
+        for (int i = 0; i < 10; i++) {
+            assertTrue(set.contains(i * 100));
+        }
+    }
+
     @Test
     public void testRemove() {
         SequenceSet set = new SequenceSet();