HBASE-21658 Should get the meta replica number from zk instead of config at client side

hbase-client/src/main/java/org/apache/hadoop/hbase/client/ZKAsyncRegistry.java

@@ -26,7 +26,9 @@ import static org.apache.hadoop.hbase.util.FutureUtils.addListener;
 import static org.apache.hadoop.hbase.zookeeper.ZKMetadata.removeMetaData;
 
 import java.io.IOException;
+import java.util.List;
 import java.util.concurrent.CompletableFuture;
+import java.util.stream.Collectors;
 import org.apache.commons.lang3.mutable.MutableInt;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.hbase.ClusterId;
@@ -134,12 +136,13 @@ class ZKAsyncRegistry implements AsyncRegistry {
       ServerName.valueOf(snProto.getHostName(), snProto.getPort(), snProto.getStartCode()));
   }
 
-  @Override
-  public CompletableFuture<RegionLocations> getMetaRegionLocation() {
-    CompletableFuture<RegionLocations> future = new CompletableFuture<>();
-    HRegionLocation[] locs = new HRegionLocation[znodePaths.metaReplicaZNodes.size()];
+  private void getMetaRegionLocation(CompletableFuture<RegionLocations> future,
+      List<String> metaReplicaZNodes) {
+    HRegionLocation[] locs = new HRegionLocation[metaReplicaZNodes.size()];
     MutableInt remaining = new MutableInt(locs.length);
-    znodePaths.metaReplicaZNodes.forEach((replicaId, path) -> {
+    for (String metaReplicaZNode : metaReplicaZNodes) {
+      int replicaId = znodePaths.getMetaReplicaIdFromZnode(metaReplicaZNode);
+      String path = ZNodePaths.joinZNode(znodePaths.baseZNode, metaReplicaZNode);
       if (replicaId == DEFAULT_REPLICA_ID) {
         addListener(getAndConvert(path, ZKAsyncRegistry::getMetaProto), (proto, error) -> {
           if (error != null) {
@@ -186,6 +189,22 @@ class ZKAsyncRegistry implements AsyncRegistry {
           tryComplete(remaining, locs, future);
         });
       }
+    }
+  }
+
+  @Override
+  public CompletableFuture<RegionLocations> getMetaRegionLocation() {
+    CompletableFuture<RegionLocations> future = new CompletableFuture<>();
+    addListener(
+      zk.list(znodePaths.baseZNode)
+        .thenApply(children -> children.stream()
+          .filter(c -> c.startsWith(znodePaths.metaZNodePrefix)).collect(Collectors.toList())),
+      (metaReplicaZNodes, error) -> {
+        if (error != null) {
+          future.completeExceptionally(error);
+          return;
+        }
+        getMetaRegionLocation(future, metaReplicaZNodes);
       });
     return future;
   }

hbase-client/src/main/java/org/apache/hadoop/hbase/zookeeper/ReadOnlyZKClient.java

@@ -24,6 +24,7 @@ import java.io.Closeable;
 import java.io.IOException;
 import java.util.Arrays;
 import java.util.EnumSet;
+import java.util.List;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.DelayQueue;
 import java.util.concurrent.Delayed;
@@ -284,6 +285,22 @@ public final class ReadOnlyZKClient implements Closeable {
     return future;
   }
 
+  public CompletableFuture<List<String>> list(String path) {
+    if (closed.get()) {
+      return FutureUtils.failedFuture(new DoNotRetryIOException("Client already closed"));
+    }
+    CompletableFuture<List<String>> future = new CompletableFuture<>();
+    tasks.add(new ZKTask<List<String>>(path, future, "list") {
+
+      @Override
+      protected void doExec(ZooKeeper zk) {
+        zk.getChildren(path, false, (rc, path, ctx, children) -> onComplete(zk, rc, children, true),
+          null);
+      }
+    });
+    return future;
+  }
+
   private void closeZk() {
     if (zookeeper != null) {
       try {

hbase-client/src/main/java/org/apache/hadoop/hbase/zookeeper/ZNodePaths.java

@@ -166,7 +166,7 @@ public class ZNodePaths {
 
   /**
    * Parse the meta replicaId from the passed znode
-   * @param znode
+   * @param znode the name of the znode, does not include baseZNode
    * @return replicaId
    */
   public int getMetaReplicaIdFromZnode(String znode) {
@@ -178,7 +178,7 @@ public class ZNodePaths {
 
   /**
    * Is it the default meta replica's znode
-   * @param znode
+   * @param znode the name of the znode, does not include baseZNode
    * @return true or false
    */
   public boolean isDefaultMetaReplicaZnode(String znode) {

hbase-server/src/test/java/org/apache/hadoop/hbase/client/TestZKAsyncRegistry.java

@@ -61,7 +61,11 @@ public class TestZKAsyncRegistry {
   public static void setUp() throws Exception {
     TEST_UTIL.getConfiguration().setInt(META_REPLICAS_NUM, 3);
     TEST_UTIL.startMiniCluster(3);
-    REGISTRY = new ZKAsyncRegistry(TEST_UTIL.getConfiguration());
+    Configuration conf = new Configuration(TEST_UTIL.getConfiguration());
+    // make sure that we do not depend on this config when getting locations for meta replicas, see
+    // HBASE-21658.
+    conf.setInt(META_REPLICAS_NUM, 1);
+    REGISTRY = new ZKAsyncRegistry(conf);
   }
 
   @AfterClass

hbase-zookeeper/src/test/java/org/apache/hadoop/hbase/zookeeper/TestReadOnlyZKClient.java

@@ -38,6 +38,8 @@ import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
 import java.io.IOException;
+import java.util.Collections;
+import java.util.List;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.Exchanger;
 import java.util.concurrent.ExecutionException;
@@ -126,9 +128,15 @@ public class TestReadOnlyZKClient {
   }
 
   @Test
-  public void testGetAndExists() throws Exception {
+  public void testRead() throws Exception {
     assertArrayEquals(DATA, RO_ZK.get(PATH).get());
     assertEquals(CHILDREN, RO_ZK.exists(PATH).get().getNumChildren());
+    List<String> children = RO_ZK.list(PATH).get();
+    assertEquals(CHILDREN, children.size());
+    Collections.sort(children);
+    for (int i = 0; i < CHILDREN; i++) {
+      assertEquals("c" + i, children.get(i));
+    }
     assertNotNull(RO_ZK.zookeeper);
     waitForIdleConnectionClosed();
   }
@@ -145,6 +153,15 @@ public class TestReadOnlyZKClient {
       assertEquals(Code.NONODE, ke.code());
       assertEquals(pathNotExists, ke.getPath());
     }
+    try {
+      RO_ZK.list(pathNotExists).get();
+      fail("should fail because of " + pathNotExists + " does not exist");
+    } catch (ExecutionException e) {
+      assertThat(e.getCause(), instanceOf(KeeperException.class));
+      KeeperException ke = (KeeperException) e.getCause();
+      assertEquals(Code.NONODE, ke.code());
+      assertEquals(pathNotExists, ke.getPath());
+    }
     // exists will not throw exception.
     assertNull(RO_ZK.exists(pathNotExists).get());
   }