[GitHub] [hbase] Apache9 commented on a diff in pull request #4556: HBASE-26913 Replication Observability Framework

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

Apache9 commented on code in PR #4556:
URL: https://github.com/apache/hbase/pull/4556#discussion_r914434308


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hbase-server/src/main/java/org/apache/hadoop/hbase/replication/regionserver/ReplicationMarkerChore.java:
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@@ -0,0 +1,118 @@
+/*
+ * 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.hbase.replication.regionserver;
+
+import static org.apache.hadoop.hbase.replication.master.ReplicationSinkTrackerTableCreator.REPLICATION_SINK_TRACKER_TABLE_NAME;
+
+import java.io.IOException;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.hbase.ScheduledChore;
+import org.apache.hadoop.hbase.Stoppable;
+import org.apache.hadoop.hbase.client.RegionInfo;
+import org.apache.hadoop.hbase.client.RegionInfoBuilder;
+import org.apache.hadoop.hbase.regionserver.MultiVersionConcurrencyControl;
+import org.apache.hadoop.hbase.regionserver.RegionServerServices;
+import org.apache.hadoop.hbase.regionserver.wal.WALUtil;
+import org.apache.hadoop.hbase.util.Bytes;
+import org.apache.hadoop.hbase.util.EnvironmentEdgeManager;
+import org.apache.hadoop.hbase.wal.WAL;
+import org.apache.hadoop.hbase.wal.WALEdit;
+import org.apache.yetus.audience.InterfaceAudience;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * This chore is responsible to create replication marker rows with special WALEdit with family as
+ * {@link org.apache.hadoop.hbase.wal.WALEdit#METAFAMILY} and column qualifier as
+ * {@link WALEdit#REPLICATION_MARKER} and empty value. If config key
+ * {@link #REPLICATION_MARKER_ENABLED_KEY} is set to true, then we will create 1 marker row every
+ * {@link #REPLICATION_MARKER_CHORE_DURATION_KEY} ms
+ * {@link org.apache.hadoop.hbase.replication.regionserver.ReplicationSourceWALReader} will populate
+ * the Replication Marker edit with region_server_name, wal_name and wal_offset encoded in
+ * {@link org.apache.hadoop.hbase.shaded.protobuf.generated.WALProtos.ReplicationMarkerDescriptor}
+ * object. {@link org.apache.hadoop.hbase.replication.regionserver.Replication} will change the
+ * REPLICATION_SCOPE for this edit to GLOBAL so that it can replicate. On the sink cluster,
+ * {@link org.apache.hadoop.hbase.replication.regionserver.ReplicationSink} will convert the
+ * ReplicationMarkerDescriptor into a Put mutation to REPLICATION_SINK_TRACKER_TABLE_NAME_STR table.
+ */
+@InterfaceAudience.Private
+public class ReplicationMarkerChore extends ScheduledChore {
+  private static final Logger LOG = LoggerFactory.getLogger(ReplicationMarkerChore.class);
+  private static final MultiVersionConcurrencyControl MVCC = new MultiVersionConcurrencyControl();
+  public static final RegionInfo REGION_INFO =
+    RegionInfoBuilder.newBuilder(REPLICATION_SINK_TRACKER_TABLE_NAME).build();
+  private static final String DELIMITER = "_";
+  private final Configuration conf;
+  private final RegionServerServices rsServices;
+  private WAL wal;
+
+  public static final String REPLICATION_MARKER_ENABLED_KEY =
+    "hbase.regionserver.replication.marker.enabled";
+  public static final boolean REPLICATION_MARKER_ENABLED_DEFAULT = false;
+
+  public static final String REPLICATION_MARKER_CHORE_DURATION_KEY =
+    "hbase.regionserver.replication.marker.chore.duration";
+  public static final int REPLICATION_MARKER_CHORE_DURATION_DEFAULT = 30 * 1000; // 30 seconds
+
+  public ReplicationMarkerChore(final Stoppable stopper, final RegionServerServices rsServices,
+    int period, Configuration conf) {
+    super("ReplicationTrackerChore", stopper, period);
+    this.conf = conf;
+    this.rsServices = rsServices;
+  }
+
+  @Override
+  protected void chore() {
+    if (wal == null) {
+      try {
+        wal = rsServices.getWAL(null);
+      } catch (IOException ioe) {
+        LOG.warn("Unable to get WAL ", ioe);
+        // Shouldn't happen. Ignore and wait for the next chore run.
+        return;
+      }
+    }
+    String serverName = rsServices.getServerName().getServerName();
+    long timeStamp = EnvironmentEdgeManager.currentTime();
+    // We only have timestamp in ReplicationMarkerDescriptor and the remaining properties walname,
+    // regionserver name and wal offset at ReplicationSourceWALReaderThread.
+    byte[] rowKey = getRowKey(serverName, timeStamp);
+    if (LOG.isTraceEnabled()) {
+      LOG.trace("Creating replication marker edit.");
+    }
+    try {
+      WALUtil.writeReplicationMarkerAndSync(wal, MVCC, REGION_INFO, rowKey, timeStamp);

Review Comment:
   The main problem here is whether we allow writing WAL entries which are not bound to a region. In the current region server architecture, when we want to get a WAL instance, we need to have a region right?
   
   So this is the main concern here. Either we change the abstraction to allow writing WAL entries which are not bound to a region, or we change the the implementation here, for example, maybe attach the marker to an existing WAL entry?



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