[GitHub] [hadoop-ozone] avijayanhwx commented on a change in pull request #1322: HDDS-3829. Introduce Layout Feature interface in Ozone.

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avijayanhwx commented on a change in pull request #1322:
URL: https://github.com/apache/hadoop-ozone/pull/1322#discussion_r480488966



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File path: hadoop-hdds/common/src/main/java/org/apache/hadoop/ozone/upgrade/AbstractLayoutVersionManager.java
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@@ -0,0 +1,110 @@
+/**
+ * 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.upgrade;
+
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.Map;
+import java.util.Optional;
+import java.util.TreeMap;
+
+import com.google.common.base.Preconditions;
+
+/**
+ * Layout Version Manager containing generic method implementations.
+ */
+@SuppressWarnings("visibilitymodifier")
+public abstract class AbstractLayoutVersionManager implements
+    LayoutVersionManager {
+
+  protected int metadataLayoutVersion; // MLV.
+  protected int softwareLayoutVersion; // SLV.
+  protected TreeMap<Integer, LayoutFeature> features = new TreeMap<>();
+  protected Map<String, LayoutFeature> featureMap = new HashMap<>();
+  protected volatile boolean isInitialized = false;
+
+  protected void init(int version, LayoutFeature[] lfs) {
+    if (!isInitialized) {
+      metadataLayoutVersion = version;
+      initializeFeatures(lfs);
+      softwareLayoutVersion = features.lastKey();
+      isInitialized = true;
+    }
+  }
+
+  protected void initializeFeatures(LayoutFeature[] lfs) {
+    Arrays.stream(lfs).forEach(f -> {
+      Preconditions.checkArgument(!featureMap.containsKey(f.name()));
+      Preconditions.checkArgument(!features.containsKey(f.layoutVersion()));
+      features.put(f.layoutVersion(), f);
+      featureMap.put(f.name(), f);
+    });
+  }
+
+  public int getMetadataLayoutVersion() {
+    return metadataLayoutVersion;
+  }
+
+  public int getSoftwareLayoutVersion() {
+    return softwareLayoutVersion;
+  }
+
+  public boolean needsFinalization() {
+    return metadataLayoutVersion < softwareLayoutVersion;
+  }
+
+  public boolean isAllowed(LayoutFeature layoutFeature) {
+    return layoutFeature.layoutVersion() <= metadataLayoutVersion;

Review comment:
       @linyiqun It is by design that newer "layout" features cannot work in Ozone until finalize. We will have a concept of Minimum Compatible layout version in the future, which is used to denote the minimum Layout version from which you can upgrade to the current layout version. 




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