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https://issues.apache.org/jira/browse/APEXCORE-60?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15065624#comment-15065624
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ASF GitHub Bot commented on APEXCORE-60:
----------------------------------------
Github user davidyan74 commented on a diff in the pull request:
https://github.com/apache/incubator-apex-core/pull/185#discussion_r48099738
--- Diff:
common/src/main/java/com/datatorrent/common/util/DefaultDelayOperator.java ---
@@ -0,0 +1,57 @@
+/**
+ * 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 java.util.ArrayList;
+import java.util.List;
+
+/**
+ * DefaultDelayOperator. This is the version of BaseDelayOperator that
provides no data loss during recovery. It
+ * incurs a run-time cost per tuple, and all tuples of the checkpoint
window will be part of the checkpoint state.
+ * Therefore if your application can tolerate data loss at recovery,
BaseDelayOperator should be used instead.
+ */
+public class DefaultDelayOperator<T> extends BaseDelayOperator<T>
--- End diff --
WindowDataManager should have much better performance than this since it
spreads the writing of the tuples throughout the entire window.
> Iterative processing support
> ----------------------------
>
> Key: APEXCORE-60
> URL: https://issues.apache.org/jira/browse/APEXCORE-60
> Project: Apache Apex Core
> Issue Type: New Feature
> Reporter: David Yan
> Assignee: David Yan
>
> We would like to support iterative processing by introducing cycles in the
> graph (known as DAG now, but no longer if we support iterative processing).
> Initial idea is as follow:
> {noformat}
> |----|
> v |
> A -> B -> C -> D
> ^ |
> |---------|
> {noformat}
> C has two separate backward streams to A and B. The input ports of A and B
> that C connects to will have a special attribute on how many window IDs ahead
> the incoming windows should be treated as, and A and B will be responsible
> for the initial data for such input ports.
> Another idea is to have C advance the window ID on its output ports and have
> C generate the initial data on its output ports to A and B.
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