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Avoid redundant connections in ClusterConnectionManager #77196

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merged 2 commits into from
Sep 3, 2021
Merged

Avoid redundant connections in ClusterConnectionManager #77196

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8cdb9c5
Avoid redundant connections in ClusterConnectionManager
DaveCTurner Sep 2, 2021
9a3fd1d
Merge branch 'master' into 2021-09-02-avoid-redundant-connections
DaveCTurner Sep 2, 2021
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12 changes: 12 additions & 0 deletions server/src/main/java/org/elasticsearch/transport/ClusterConnectionManager.java
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Original file line number Diff line number Diff line change
Expand Up @@ -123,13 +123,25 @@ public void connectToNode(DiscoveryNode node, ConnectionProfile connectionProfil

currentListener.addListener(listener);

// It's possible that a connection completed, and the pendingConnections entry was removed, between the calls to
// connectedNodes.containsKey and pendingConnections.putIfAbsent above, so we check again to make sure we don't open a redundant
// extra connection to the node. We could _just_ check here, but checking up front skips the work to mark the connection as pending.
if (connectedNodes.containsKey(node)) {
ListenableFuture<Void> future = pendingConnections.remove(node);
assert future == currentListener : "Listener in pending map is different than the expected listener";
connectingRefCounter.decRef();
future.onResponse(null);
return;
}

final RunOnce releaseOnce = new RunOnce(connectingRefCounter::decRef);
internalOpenConnection(node, resolvedProfile, ActionListener.wrap(conn -> {
connectionValidator.validate(conn, resolvedProfile, ActionListener.wrap(
ignored -> {
assert Transports.assertNotTransportThread("connection validator success");
try {
if (connectedNodes.putIfAbsent(node, conn) != null) {
assert false : "redundant conection to " + node;
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ClusterConnectionManagerTests#testConcurrentConnects exercises this - I can make it fail reasonably often by adding a few Thread.sleep calls:

diff --git a/server/src/main/java/org/elasticsearch/transport/ClusterConnectionManager.java b/server/src/main/java/org/elasticsearch/transport/ClusterConnectionManager.java
index 415769596a4..00bb8423d7b 100644
--- a/server/src/main/java/org/elasticsearch/transport/ClusterConnectionManager.java
+++ b/server/src/main/java/org/elasticsearch/transport/ClusterConnectionManager.java
@@ -11,6 +11,7 @@ import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 import org.elasticsearch.action.ActionListener;
 import org.elasticsearch.cluster.node.DiscoveryNode;
+import org.elasticsearch.common.Randomness;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.core.AbstractRefCounted;
 import org.elasticsearch.common.util.concurrent.ConcurrentCollections;
@@ -109,6 +110,12 @@ public class ClusterConnectionManager implements ConnectionManager {
             return;
         }

+        try {
+            Thread.sleep(Randomness.get().nextInt(50));
+        } catch (InterruptedException e) {
+            throw new AssertionError("unexpected", e);
+        }
+
         final ListenableFuture<Void> currentListener = new ListenableFuture<>();
         final ListenableFuture<Void> existingListener = pendingConnections.putIfAbsent(node, currentListener);
         if (existingListener != null) {
@@ -126,7 +133,7 @@ public class ClusterConnectionManager implements ConnectionManager {
         // It's possible that a connection completed, and the pendingConnections entry was removed, between the calls to
         // connectedNodes.containsKey and pendingConnections.putIfAbsent above, so we check again to make sure we don't open a redundant
         // extra connection to the node. We could _just_ check here, but checking up front skips the work to mark the connection as pending.
-        if (connectedNodes.containsKey(node)) {
+        if (connectedNodes.containsKey(node) && false) {
             ListenableFuture<Void> future = pendingConnections.remove(node);
             assert future == currentListener : "Listener in pending map is different than the expected listener";
             connectingRefCounter.decRef();
diff --git a/server/src/test/java/org/elasticsearch/transport/ClusterConnectionManagerTests.java b/server/src/test/java/org/elasticsearch/transport/ClusterConnectionManagerTests.java
index f44217e276a..2b11867d21f 100644
--- a/server/src/test/java/org/elasticsearch/transport/ClusterConnectionManagerTests.java
+++ b/server/src/test/java/org/elasticsearch/transport/ClusterConnectionManagerTests.java
@@ -163,6 +163,7 @@ public class ClusterConnectionManagerTests extends ESTestCase {
             Thread thread = new Thread(() -> {
                 try {
                     barrier.await();
+                    Thread.sleep(between(0, 50));
                 } catch (InterruptedException | BrokenBarrierException e) {
                     throw new RuntimeException(e);
                 }

logger.debug("existing connection to node [{}], closing new redundant connection", node);
IOUtils.closeWhileHandlingException(conn);
} else {
Expand Down