[GitHub] [flink] tillrohrmann commented on a change in pull request #10754: [FLINK-14091][coordination] Allow updates to connection state when ZKCheckpointIDCounter reconnects to ZK

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tillrohrmann commented on a change in pull request #10754: [FLINK-14091][coordination] Allow updates to connection state when ZKCheckpointIDCounter reconnects to ZK
URL: https://github.com/apache/flink/pull/10754#discussion_r366362147
 
 

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 File path: flink-runtime/src/test/java/org/apache/flink/runtime/checkpoint/ZKCheckpointIDCounterMultiServersTest.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.flink.runtime.checkpoint;
+
+import org.apache.flink.runtime.zookeeper.ZooKeeperTestEnvironment;
+import org.apache.flink.util.TestLogger;
+
+import org.apache.curator.framework.CuratorFramework;
+import org.apache.curator.framework.state.ConnectionState;
+import org.apache.curator.test.TestingCluster;
+import org.junit.AfterClass;
+import org.junit.Before;
+import org.junit.Test;
+
+import java.util.concurrent.atomic.AtomicLong;
+
+import static org.hamcrest.CoreMatchers.is;
+import static org.hamcrest.CoreMatchers.notNullValue;
+import static org.junit.Assert.assertThat;
+
+/**
+ * Tests for {@link ZooKeeperCheckpointIDCounter} in a ZooKeeper ensemble.
+ */
+public final class ZKCheckpointIDCounterMultiServersTest extends TestLogger {
+
+	private static final ZooKeeperTestEnvironment ZOOKEEPER = new ZooKeeperTestEnvironment(3);
+
+	@AfterClass
+	public static void tearDown() throws Exception {
+		ZOOKEEPER.shutdown();
+	}
+
+	@Before
+	public void cleanUp() throws Exception {
+		ZOOKEEPER.deleteAll();
+	}
+
+	/**
+	 * Tests that {@link ZooKeeperCheckpointIDCounter} can be recovered after a
+	 * connection loss exception from ZooKeeper ensemble.
+	 *
+	 * See also FLINK-14091.
+	 */
+	@Test
+	public void testRecoveredAfterConnectionLoss() throws Exception {
+		CuratorFramework client = ZOOKEEPER.getClient();
+
+		ZooKeeperCheckpointIDCounter idCounter = new ZooKeeperCheckpointIDCounter(client, "/checkpoint-id-counter");
+		idCounter.start();
+
+		AtomicLong localCounter = new AtomicLong(1L);
+
+		assertThat(
+			"ZooKeeperCheckpointIDCounter doesn't properly work.",
+			idCounter.getAndIncrement(),
+			is(localCounter.getAndIncrement()));
+
+		TestingCluster cluster = ZOOKEEPER.getZooKeeperCluster();
+		assertThat(cluster, is(notNullValue()));
+
+		// close the server this client connected to, which triggers a connection loss exception
+		cluster.restartServer(cluster.findConnectionInstance(client.getZookeeperClient().getZooKeeper()));
+
+		// encountered connected loss, this prevents us from getting false positive
+		while (true) {
+			try {
+				idCounter.get();
+			} catch (IllegalStateException ignore) {
+				log.debug("Encountered connection loss.");
+				break;
+			}
+		}
+
+		// recovered from connection loss
+		while (true) {
+			try {
+				long id = idCounter.get();
+				assertThat(id, is(localCounter.get()));
+				break;
+			} catch (IllegalStateException ignore) {
+				log.debug("During ZooKeeper client reconnecting...");
+			}
+		}
+
+		assertThat(idCounter.getLastState(), is(ConnectionState.RECONNECTED));
 
 Review comment:
   I think it is not important for the test to ensure that some internal state is `RECONNECTED`. What we should try to test is that we can increment the ID counter under loss of connection but it is not important how exactly this works.

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