HBASE-20742 Always create WAL directory for region server

hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/HRegionServer.java

@@ -1813,6 +1813,11 @@ public class HRegionServer extends HasThread implements
       throw new RegionServerRunningException(
           "Region server has already created directory at " + this.serverName.toString());
     }
+    // Always create wal directory as now we need this when master restarts to find out the live
+    // region servers.
+    if (!this.walFs.mkdirs(logDir)) {
+      throw new IOException("Can not create wal directory " + logDir);
+    }
     // Instantiate replication if replication enabled. Pass it the log directories.
     createNewReplicationInstance(conf, this, this.walFs, logDir, oldLogDir,
       factory.getWALProvider());

hbase-server/src/test/java/org/apache/hadoop/hbase/regionserver/TestRegionServerCrashDisableWAL.java

@@ -0,0 +1,106 @@
+/**
+ * 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.regionserver;
+
+import static org.junit.Assert.assertEquals;
+
+import java.io.IOException;
+import org.apache.hadoop.hbase.HBaseClassTestRule;
+import org.apache.hadoop.hbase.HBaseTestingUtility;
+import org.apache.hadoop.hbase.TableName;
+import org.apache.hadoop.hbase.client.Get;
+import org.apache.hadoop.hbase.client.Put;
+import org.apache.hadoop.hbase.client.Table;
+import org.apache.hadoop.hbase.master.HMaster;
+import org.apache.hadoop.hbase.master.ServerManager;
+import org.apache.hadoop.hbase.testclassification.MediumTests;
+import org.apache.hadoop.hbase.testclassification.RegionServerTests;
+import org.apache.hadoop.hbase.util.Bytes;
+import org.apache.hadoop.hbase.util.JVMClusterUtil.RegionServerThread;
+import org.junit.AfterClass;
+import org.junit.BeforeClass;
+import org.junit.ClassRule;
+import org.junit.Test;
+import org.junit.experimental.categories.Category;
+
+/**
+ * Testcase for HBASE-20742
+ */
+@Category({ RegionServerTests.class, MediumTests.class })
+public class TestRegionServerCrashDisableWAL {
+
+  @ClassRule
+  public static final HBaseClassTestRule CLASS_RULE =
+    HBaseClassTestRule.forClass(TestRegionServerCrashDisableWAL.class);
+
+  private static final HBaseTestingUtility UTIL = new HBaseTestingUtility();
+
+  private static TableName TABLE_NAME = TableName.valueOf("test");
+
+  private static byte[] CF = Bytes.toBytes("cf");
+
+  private static byte[] CQ = Bytes.toBytes("cq");
+
+  @BeforeClass
+  public static void setUp() throws Exception {
+    UTIL.getConfiguration().setInt(ServerManager.WAIT_ON_REGIONSERVERS_MINTOSTART, 1);
+    UTIL.getConfiguration().setBoolean("hbase.regionserver.hlog.enabled", false);
+    UTIL.startMiniCluster(2);
+    UTIL.createTable(TABLE_NAME, CF);
+    UTIL.waitTableAvailable(TABLE_NAME);
+    HRegionServer rs = UTIL.getRSForFirstRegionInTable(TABLE_NAME);
+    if (!rs.getRegions(TableName.META_TABLE_NAME).isEmpty()) {
+      HRegionServer rs1 = UTIL.getOtherRegionServer(rs);
+      UTIL.moveRegionAndWait(
+        UTIL.getMiniHBaseCluster().getRegions(TABLE_NAME).get(0).getRegionInfo(),
+        rs1.getServerName());
+    }
+    UTIL.getAdmin().balancerSwitch(false, true);
+  }
+
+  @AfterClass
+  public static void tearDown() throws Exception {
+    UTIL.shutdownMiniCluster();
+  }
+
+  @Test
+  public void test() throws InterruptedException, IOException {
+    HMaster master = UTIL.getMiniHBaseCluster().stopMaster(0).getMaster();
+    // Shutdown master before shutting down rs
+    UTIL.waitFor(30000, () -> !master.isAlive());
+    RegionServerThread thread = null;
+    for (RegionServerThread t : UTIL.getMiniHBaseCluster().getRegionServerThreads()) {
+      if (!t.getRegionServer().getRegions(TABLE_NAME).isEmpty()) {
+        thread = t;
+        break;
+      }
+    }
+    // shutdown rs
+    thread.getRegionServer().abort("For testing");
+    thread.join();
+    // restart master
+    UTIL.getMiniHBaseCluster().startMaster();
+    // make sure that we can schedule a SCP for the crashed server which WAL is disabled and bring
+    // the region online.
+    try (Table table =
+      UTIL.getConnection().getTableBuilder(TABLE_NAME, null).setOperationTimeout(30000).build()) {
+      table.put(new Put(Bytes.toBytes(1)).addColumn(CF, CQ, Bytes.toBytes(1)));
+      assertEquals(1, Bytes.toInt(table.get(new Get(Bytes.toBytes(1))).getValue(CF, CQ)));
+    }
+  }
+}