Github user davidyan74 commented on a diff in the pull request:
https://github.com/apache/incubator-apex-core/pull/185#discussion_r47808468
--- Diff:
common/src/main/java/com/datatorrent/common/util/SimpleDelayOperator.java ---
@@ -0,0 +1,59 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package com.datatorrent.common.util;
+
+import com.datatorrent.api.DefaultInputPort;
+import com.datatorrent.api.DefaultOutputPort;
+import com.datatorrent.api.Operator;
+
+/**
+ * SimpleDelayOperator. This is an implementation of the DelayOperator
that has one input port and one output
+ * port, and does a simple pass-through from the input port to the output
port. Subclass of this operator can
+ * override this behavior by overriding processTuple(T tuple).
+ *
+ * Since the firstWindow method does not do anything, using this operator
as-is means data loss during recovery. In
+ * order to achieve zero data loss during recovery, implementations must
persist relevant tuples before the recovery
+ * checkpoint for emitting during the first window after recovery.
+ *
+ * Note that the engine will automatically does a +1 on the output window
ID since it is a DelayOperator.
--- End diff --
done. need to brush up my grammar. :)
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