Fix a bug in object reuse in CompositeByteBuffer (#48)

The buffer size should be less than or equal to the new size for object reuse to utilize the existing buffer in CompositeByteBuffer. The bug was that we previously did not check for equality, leading to spurious memory allocation in the common case where we attempt to reuse arrays with the same number of elements.

avro-fastserde/src/main/java/com/linkedin/avro/fastserde/CompositeByteBuffer.java

@@ -19,7 +19,7 @@ public ByteBuffer allocate(int index, int size) {
     ByteBuffer byteBuffer;
 
     // Check if we can reuse the old record's byteBuffers, else allocate a new one.
-    if (byteBuffers.size() > index && byteBuffers.get(index).capacity() > size) {
+    if (byteBuffers.size() > index && byteBuffers.get(index).capacity() >= size) {
       byteBuffer = byteBuffers.get(index);
       byteBuffer.clear();
     } else {

avro-fastserde/src/test/java/com/linkedin/avro/fastserde/FastDeserializerGeneratorForReuseTest.java

@@ -204,14 +204,16 @@ public void testFastGenericDeserializerPrimitFloatList() throws Exception {
     List<Float> list = (List<Float>)genericRecord.get(1);
     Assert.assertEquals(list.size(), 3);
 
-    // new record array length shorter than reuse record.
+    // new record array length same as before for reusing byte buffers
     arrayList.clear();
     arrayList.add((float)10);
+    arrayList.add((float)20);
+    arrayList.add((float)30);
     record1.put("inventory", arrayList);
     serializedBytes = serialize(record1, oldRecordSchema);
     genericRecord = deserializer.deserialize(deserRecord, getDecoder(serializedBytes));
     list = (List<Float>)genericRecord.get(1);
-    Assert.assertEquals(list.size(), 1);
+    Assert.assertEquals(list.size(), 3);
 
   }
 }