[GitHub] [hbase] Apache9 commented on a change in pull request #1774: HBASE-24389 Introduce a new master rpc service to locate meta region through root region

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Apache9 commented on a change in pull request #1774:
URL: https://github.com/apache/hbase/pull/1774#discussion_r432188121



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File path: hbase-client/src/main/java/org/apache/hadoop/hbase/client/AbstractAsyncTableRegionLocator.java
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@@ -0,0 +1,308 @@
+/**
+ * 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.client;
+
+import static org.apache.hadoop.hbase.HConstants.EMPTY_END_ROW;
+import static org.apache.hadoop.hbase.client.AsyncRegionLocatorHelper.isGood;
+import static org.apache.hadoop.hbase.client.ConnectionUtils.createClosestRowAfter;
+
+import java.io.IOException;
+import java.util.HashSet;
+import java.util.Iterator;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.Set;
+import java.util.concurrent.CompletableFuture;
+import org.apache.commons.lang3.ObjectUtils;
+import org.apache.hadoop.hbase.HBaseIOException;
+import org.apache.hadoop.hbase.HRegionLocation;
+import org.apache.hadoop.hbase.RegionLocations;
+import org.apache.hadoop.hbase.ServerName;
+import org.apache.hadoop.hbase.TableName;
+import org.apache.hadoop.hbase.util.Bytes;
+import org.apache.yetus.audience.InterfaceAudience;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import org.apache.hbase.thirdparty.com.google.common.annotations.VisibleForTesting;
+
+/**
+ * The base class for locating region of a table.
+ */
+@InterfaceAudience.Private
+abstract class AbstractAsyncTableRegionLocator {
+
+  private static final Logger LOG = LoggerFactory.getLogger(AbstractAsyncTableRegionLocator.class);
+
+  protected final AsyncConnectionImpl conn;
+
+  protected final TableName tableName;
+
+  protected final int maxConcurrent;
+
+  protected final TableRegionLocationCache cache;
+
+  protected static final class LocateRequest {

Review comment:
       Not now, the locateType is introduced at the same time with async client, for isolating all the locating related logic from upper layer. The magic is to construct different Scan object, with modified startRow, or include/exclude the startRow.
   
   We have to support this, one of the most important reason is for supporting reverse scan, where we need to locate the region before the current region, but what we have is the start row of the current region, which is not part of the region before, so we need to use LocateType.BEFORE to get the location.




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