[GitHub] [incubator-ratis] joshelser commented on a change in pull request #25: RATIS-588 LogStream StateMachine export

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joshelser commented on a change in pull request #25: RATIS-588 LogStream StateMachine export
URL: https://github.com/apache/incubator-ratis/pull/25#discussion_r294368193
 
 

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 File path: ratis-logservice/src/main/java/org/apache/ratis/logservice/impl/ArchiveHdfsLogWriter.java
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+/**
+ * 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.ratis.logservice.impl;
+
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.util.ArrayList;
+import java.util.List;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.FSDataOutputStream;
+import org.apache.hadoop.fs.FileSystem;
+import org.apache.hadoop.fs.Path;
+import org.apache.ratis.logservice.api.ArchiveLogWriter;
+import org.apache.ratis.logservice.api.LogName;
+import org.apache.ratis.logservice.util.LogServiceUtils;
+
+public class ArchiveHdfsLogWriter implements ArchiveLogWriter {
+  private FileSystem hdfs;
+  private FSDataOutputStream os;
+  private Path currentPath;
+  private long currentRecordId;
+  private long lastRollRecordId;
+
+  @Override
+  public void init(String location, LogName logName) throws IOException {
+    Configuration configuration = new Configuration();
+    hdfs = FileSystem.get(configuration);
+    currentPath = new Path(location + "/" + logName.getName());
+    os = hdfs.create(currentPath,true);
+  }
+
+  @Override public long write(ByteBuffer data) throws IOException {
+    os.writeInt(data.array().length);
+    os.write(data.array());
+    currentRecordId++;
+    return currentRecordId;
+  }
+
+  @Override public List<Long> write(List<ByteBuffer> records) throws IOException {
+    List<Long> list = new ArrayList<Long>();
+    for (ByteBuffer record : records) {
+      list.add(write(record));
+    }
+    return list;
+  }
+
+  @Override public long sync() throws IOException {
+    return 0;
+  }
+
+  @Override public void close() throws IOException {
+    os.close();
+    renameIfNewData();
+    hdfs.close();
+  }
+
+  @Override public void rollWriter() throws IOException {
+    //close old file
+    os.close();
+    renameIfNewData();
+    lastRollRecordId = currentRecordId;
+    //create new file
+    os = hdfs.create(currentPath, true);
+  }
+
+  @Override public long getLastWrittenRecordId() {
+    return currentRecordId;
 
 Review comment:
   Just a thought -- until we call `close()` on the outputstream, this won't be accurate for multi-threaded invocations. Same sort of problem we have in WALs in HBase.
   
   As long as we aren't trying to read from a Log from HDFS while it's in the ARCHIVING state, I don't think this is an issue. If we wanted to do that, I think we'd have to call `hflush` to make this "honest".

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