[GitHub] [hadoop-ozone] arp7 commented on a change in pull request #7: HDDS-1228. Chunk Scanner Checkpoints

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arp7 commented on a change in pull request #7: HDDS-1228. Chunk Scanner Checkpoints
URL: https://github.com/apache/hadoop-ozone/pull/7#discussion_r337312099
 
 

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 File path: hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/common/impl/ContainerDataScanOrder.java
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 @@ -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 org.apache.hadoop.ozone.container.common.impl;
+
+import org.apache.hadoop.ozone.container.common.interfaces.Container;
+
+import java.time.Instant;
+import java.util.Comparator;
+import java.util.Optional;
+
+/**
+ * Orders containers:
+ * 1. containers not yet scanned first,
+ * 2. then least recently scanned first,
+ * 3. ties are broken by containerID.
+ */
+public class ContainerDataScanOrder implements Comparator<Container<?>> {
+
+  public static final Comparator<Container<?>> INSTANCE =
+      new ContainerDataScanOrder();
+
+  @Override
+  public int compare(Container<?> o1, Container<?> o2) {
+    ContainerData d1 = o1.getContainerData();
+    ContainerData d2 = o2.getContainerData();
+
+    Optional<Instant> scan1 = d1.lastDataScanTime();
+    boolean scanned1 = scan1.isPresent();
+    Optional<Instant> scan2 = d2.lastDataScanTime();
+    boolean scanned2 = scan2.isPresent();
+
+    int result = Boolean.compare(scanned1, scanned2);
+    if (0 == result && scanned1 && scanned2) {
+      result = scan1.get().compareTo(scan2.get());
+    }
+    if (0 == result) {
+      result = Long.compare(d1.getContainerID(), d2.getContainerID());
 
 Review comment:
   I think this check is incomplete. If scanned1 is absent however scanned2 is present, then o1 should order before o2, irrespective of their container IDs.

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