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

[GitBox <gi...@apache.org>]

errose28 commented on a change in pull request #1613:
URL: https://github.com/apache/ozone/pull/1613#discussion_r530602103



##########
File path: hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/request/upgrade/OMPrepareRequest.java
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@@ -0,0 +1,108 @@
+package org.apache.hadoop.ozone.om.request.upgrade;
+
+import org.apache.hadoop.hdds.ratis.RatisUpgradeUtils;
+import org.apache.hadoop.ozone.om.OzoneManager;
+import org.apache.hadoop.ozone.om.exceptions.OMException;
+import org.apache.hadoop.ozone.om.ratis.OzoneManagerRatisServer;
+import org.apache.hadoop.ozone.om.ratis.OzoneManagerStateMachine;
+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.protocol.proto.OzoneManagerProtocolProtos.Type;
+
+import org.apache.ratis.server.impl.RaftServerImpl;
+import org.apache.ratis.server.impl.RaftServerProxy;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.IOException;
+
+/**
+ * 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 long DOUBLE_BUFFER_FLUSH_TIMEOUT_SECONDS = 5 * 60;
+  // Time between checks to see if double buffer finished flushing.
+  private static final long DOUBLE_BUFFER_FLUSH_CHECK_SECONDS = 1;
+
+  public OMPrepareRequest(OMRequest omRequest) {
+    super(omRequest);
+  }
+
+  @Override
+  public OMClientResponse validateAndUpdateCache(
+      OzoneManager ozoneManager, long transactionLogIndex,
+      OzoneManagerDoubleBufferHelper ozoneManagerDoubleBufferHelper) {
+
+    LOG.info("Received prepare request with log index {}", transactionLogIndex);
+
+    OMResponse.Builder responseBuilder =
+        OmResponseUtil.getOMResponseBuilder(getOmRequest());
+    responseBuilder.setCmdType(Type.Prepare);
+    OMClientResponse response = null;
+
+    try {
+      // Create response.
+      PrepareResponse omResponse = PrepareResponse.newBuilder()
+              .setTxnID(transactionLogIndex)
+              .build();
+      responseBuilder.setPrepareForUpgradeResponse(omResponse);
+      response = new OMPrepareResponse(responseBuilder.build());
+
+      // Add response to double buffer before clearing logs.
+      // This guarantees the log index of this request will be the same as
+      // the snapshot index in the prepared state.
+      ozoneManagerDoubleBufferHelper.add(response, transactionLogIndex);
+
+      OzoneManagerRatisServer omRatisServer = ozoneManager.getOmRatisServer();
+      OzoneManagerStateMachine omStateMachine =
+          omRatisServer.getOmStateMachine();
+      RaftServerProxy server = (RaftServerProxy) omRatisServer.getServer();
+      RaftServerImpl serverImpl =
+          server.getImpl(omRatisServer.getRaftGroup().getGroupId());
+
+      // Wait for outstanding double buffer entries to flush to disk,
+      // so they will not be purged from the log before being persisted to
+      // the DB.
+      RatisUpgradeUtils.waitForAllTxnsApplied(omStateMachine, serverImpl,
+          DOUBLE_BUFFER_FLUSH_TIMEOUT_SECONDS,
+          DOUBLE_BUFFER_FLUSH_CHECK_SECONDS);

Review comment:
       Yes Yiqun, you are right. This was an early draft of the feature. Please see the new code and let me know if this resolves your concern.




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