[GitHub] [ozone] errose28 commented on a change in pull request #1613: HDDS-4480. Implement OM Prepare Request/Response.

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errose28 commented on a change in pull request #1613:
URL: https://github.com/apache/ozone/pull/1613#discussion_r533693610



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File path: hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/request/upgrade/OMPrepareRequest.java
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@@ -0,0 +1,196 @@
+/*
+ * 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
+ * <p>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * 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.om.request.upgrade;
+
+import org.apache.hadoop.ozone.om.OzoneManager;
+import org.apache.hadoop.ozone.om.exceptions.OMException;
+import org.apache.hadoop.ozone.om.ratis.OMTransactionInfo;
+import org.apache.hadoop.ozone.om.ratis.OzoneManagerRatisServer;
+import org.apache.hadoop.ozone.om.ratis.utils.OzoneManagerDoubleBufferHelper;
+import org.apache.hadoop.ozone.om.request.OMClientRequest;
+import org.apache.hadoop.ozone.om.request.util.OmResponseUtil;
+import org.apache.hadoop.ozone.om.response.OMClientResponse;
+import org.apache.hadoop.ozone.om.response.upgrade.OMPrepareResponse;
+import org.apache.hadoop.ozone.protocol.proto.OzoneManagerProtocolProtos.PrepareResponse;
+import org.apache.hadoop.ozone.protocol.proto.OzoneManagerProtocolProtos.OMRequest;
+import org.apache.hadoop.ozone.protocol.proto.OzoneManagerProtocolProtos.OMResponse;
+
+import static org.apache.hadoop.ozone.OzoneConsts.TRANSACTION_INFO_KEY;
+import static org.apache.hadoop.ozone.protocol.proto.OzoneManagerProtocolProtos.Type;
+
+import org.apache.ratis.server.impl.RaftServerImpl;
+import org.apache.ratis.server.impl.RaftServerProxy;
+import org.apache.ratis.server.raftlog.RaftLog;
+import org.apache.ratis.statemachine.StateMachine;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.IOException;
+import java.time.Duration;
+import java.time.temporal.ChronoUnit;
+import java.util.concurrent.CompletableFuture;
+
+/**
+ * OM Request used to flush all transactions to disk, take a DB snapshot, and
+ * purge the logs, leaving Ratis in a clean state without unapplied log
+ * entries. This prepares the OM for upgrades/downgrades so that no request
+ * in the log is applied to the database in the old version of the code in one
+ * OM, and the new version of the code on another OM.
+ */
+public class OMPrepareRequest extends OMClientRequest {
+  private static final Logger LOG =
+      LoggerFactory.getLogger(OMPrepareRequest.class);
+
+  // Allow double buffer this many seconds to flush all transactions before
+  // returning an error to the caller.
+  private static final Duration DOUBLE_BUFFER_FLUSH_TIMEOUT =

Review comment:
       I can make this an external config if we think it is necessary. @avijayanhwx any thoughts here?




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