ZOOKEEPER-4511: Fix flaky test FileTxnSnapLogMetricsTest.testFileTxnSnapLogMetrics

This test writes txns to trigger snapshot and expects some txns remain
in txn log. But snapshot taking is asynchronous, thus all txns could be
written to snapshot. So in restarting, it is possible that no txns to
load after snapshot restored. This will fail assertion.

This commit solves this by disable automic snapshot taking by
`SyncRequestProcessor.setSnapCount(Integer.MAX_VALUE)`.

Author: Kezhu Wang <kezhuw@gmail.com>

Reviewers: Enrico Olivelli <eolivelli@apache.org>, Mate Szalay-Beko <symat@apache.org>

Closes #1852 from kezhuw/ZOOKEEPER-4511-FileTxnSnapLogMetricsTest-testFileTxnSnapLogMetrics

zookeeper-server/src/test/java/org/apache/zookeeper/ZKTestCase.java

@@ -21,7 +21,7 @@ package org.apache.zookeeper;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 import static org.junit.jupiter.api.Assertions.fail;
 import java.io.File;
-import java.time.LocalDateTime;
+import java.time.Instant;
 import org.apache.zookeeper.util.ServiceUtils;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeAll;
@@ -100,8 +100,8 @@ public class ZKTestCase {
      * @throws InterruptedException
      */
     public void waitFor(String msg, WaitForCondition condition, int timeout) throws InterruptedException {
-        final LocalDateTime deadline = LocalDateTime.now().plusSeconds(timeout);
-        while (LocalDateTime.now().isBefore(deadline)) {
+        final Instant deadline = Instant.now().plusSeconds(timeout);
+        while (Instant.now().isBefore(deadline)) {
             if (condition.evaluate()) {
                 return;
             }

zookeeper-server/src/test/java/org/apache/zookeeper/server/persistence/FileTxnSnapLogMetricsTest.java

@@ -22,20 +22,21 @@ import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.number.OrderingComparison.greaterThan;
 import static org.hamcrest.number.OrderingComparison.greaterThanOrEqualTo;
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import java.io.File;
 import java.util.Map;
-import java.util.concurrent.CountDownLatch;
 import org.apache.zookeeper.CreateMode;
-import org.apache.zookeeper.WatchedEvent;
-import org.apache.zookeeper.Watcher;
 import org.apache.zookeeper.ZKTestCase;
 import org.apache.zookeeper.ZooDefs;
 import org.apache.zookeeper.ZooKeeper;
 import org.apache.zookeeper.metrics.MetricsUtils;
+import org.apache.zookeeper.server.ServerCnxnFactory;
 import org.apache.zookeeper.server.ServerMetrics;
 import org.apache.zookeeper.server.SyncRequestProcessor;
+import org.apache.zookeeper.server.ZooKeeperServer;
 import org.apache.zookeeper.test.ClientBase;
-import org.apache.zookeeper.test.QuorumUtil;
+import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -43,43 +44,53 @@ public class FileTxnSnapLogMetricsTest extends ZKTestCase {
 
     private static final Logger LOG = LoggerFactory.getLogger(FileTxnSnapLogMetricsTest.class);
 
-    CountDownLatch allCreatedLatch;
+    @TempDir
+    File logDir;
 
-    private class MockWatcher implements Watcher {
+    @TempDir
+    File snapDir;
 
-        @Override
-        public void process(WatchedEvent e) {
-            LOG.info("all nodes created");
-            allCreatedLatch.countDown();
-        }
+    private ServerCnxnFactory startServer() throws Exception {
+        ZooKeeperServer zkServer = new ZooKeeperServer(snapDir, logDir, 3000);
+        ServerCnxnFactory cnxnFactory = ServerCnxnFactory.createFactory(0, -1);
+        cnxnFactory.startup(zkServer);
+        return cnxnFactory;
+    }
 
+    @AfterEach
+    public void cleanup() throws Exception {
+        SyncRequestProcessor.setSnapCount(ZooKeeperServer.getSnapCount());
     }
 
     @Test
     public void testFileTxnSnapLogMetrics() throws Exception {
         SyncRequestProcessor.setSnapCount(100);
 
-        QuorumUtil util = new QuorumUtil(1);
-        util.startAll();
+        ServerCnxnFactory cnxnFactory = startServer();
+        String connectString = "127.0.0.1:" + cnxnFactory.getLocalPort();
 
-        allCreatedLatch = new CountDownLatch(1);
+        // Snapshot in load data.
+        assertEquals(1L, MetricsUtils.currentServerMetrics().get("cnt_snapshottime"));
 
         byte[] data = new byte[500];
-        // make sure a snapshot is taken and some txns are not in a snapshot
-        ZooKeeper zk = ClientBase.createZKClient(util.getConnString());
+        ZooKeeper zk = ClientBase.createZKClient(connectString);
         for (int i = 0; i < 150; i++) {
             zk.create("/path" + i, data, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
         }
 
-        if (null == zk.exists("/path149", new MockWatcher())) {
-            allCreatedLatch.await();
-        }
+        // It is possible that above writes will trigger more than one snapshot due to randomization.
+        WaitForCondition newSnapshot = () -> (long) MetricsUtils.currentServerMetrics().get("cnt_snapshottime") >= 2L;
+        waitFor("no snapshot in 10s", newSnapshot, 10);
+
+        // Pauses snapshot and logs more txns.
+        cnxnFactory.getZooKeeperServer().getTxnLogFactory().snapLog.close();
+        zk.create("/" + 1000, data, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
+        zk.create("/" + 1001, data, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
 
+        // Restart server to count startup metrics.
+        cnxnFactory.shutdown();
         ServerMetrics.getMetrics().resetAll();
-        int leader = util.getLeaderServer();
-        // restart a server so it will read the snapshot and the txn logs
-        util.shutdown(leader);
-        util.start(leader);
+        cnxnFactory = startServer();
 
         Map<String, Object> values = MetricsUtils.currentServerMetrics();
         LOG.info("txn loaded during start up {}", values.get("max_startup_txns_loaded"));
@@ -90,7 +101,7 @@ public class FileTxnSnapLogMetricsTest extends ZKTestCase {
         assertEquals(1L, values.get("cnt_startup_snap_load_time"));
         assertThat((long) values.get("max_startup_snap_load_time"), greaterThan(0L));
 
-        util.shutdownAll();
+        cnxnFactory.shutdown();
     }
 
 }