[GitHub] [samza] bkonold commented on a change in pull request #1413: SAMZA-2578: Excessive trimming during transactional state restore

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bkonold commented on a change in pull request #1413:
URL: https://github.com/apache/samza/pull/1413#discussion_r472574677



##########
File path: samza-api/src/main/java/org/apache/samza/system/BoundedSSPIterator.java
##########
@@ -0,0 +1,84 @@
+/*
+ * 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 org.apache.samza.system;
+
+import java.util.ArrayDeque;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.NoSuchElementException;
+import java.util.Queue;
+import java.util.Set;
+import org.apache.samza.SamzaException;
+
+/**
+ * Iterates over messages in the provided changelog {@link SystemStreamPartition} using the provided
+ * {@link SystemConsumer} until all messages with offsets up to and including the bound offset have been consumed.
+ */
+public class BoundedSSPIterator {
+
+  protected final SystemAdmin admin;
+
+  private final SystemConsumer systemConsumer;
+  private final String endOffset;
+  private final Set<SystemStreamPartition> fetchSet;
+  private Queue<IncomingMessageEnvelope> peeks;
+
+  public BoundedSSPIterator(SystemConsumer systemConsumer,
+      SystemStreamPartition systemStreamPartition, String endOffset, SystemAdmin admin) {
+    this.systemConsumer = systemConsumer;
+    this.endOffset = endOffset;
+    this.admin = admin;
+    this.fetchSet = new HashSet<>();
+    this.fetchSet.add(systemStreamPartition);

Review comment:
       Good point. I just pulled this out of ChangelogSSPIterator. The API for SystemConsume.poll does call for a set, so having a set here would prevent redundant object creation if we were to store a single SSP as member and create a set every time we call poll.
   
   I don't see a problem keeping this as a set here, but maybe we could change the initialization to be a singleton set / immutable set?




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