From 32c65d7b606180523a2520e338bfa0f79e0cbfd1 Mon Sep 17 00:00:00 2001
From: Alex Castillo <alex.castillog33@gmail.com>
Date: Sat, 7 Nov 2026 00:37:47 -0400
Subject: [PATCH] fix(client-v2): record connection times only when metrics are
 enabled

---
 .../api/internal/HttpAPIClientHelper.java     | 11 ++++++
 .../MeteredConnectionFactoryTest.java         | 38 +++++++++++++++++++
 history/latest/3253.md                        |  4 ++
 3 files changed, 53 insertions(+)
 create mode 100644 client-v2/src/test/java/com/clickhouse/client/api/internal/MeteredConnectionFactoryTest.java
 create mode 100644 history/latest/3253.md

diff --git a/client-v2/src/main/java/com/clickhouse/client/api/internal/HttpAPIClientHelper.java b/client-v2/src/main/java/com/clickhouse/client/api/internal/HttpAPIClientHelper.java
index 07f8e4f54..20f33ce53 100644
--- a/client-v2/src/main/java/com/clickhouse/client/api/internal/HttpAPIClientHelper.java
+++ b/client-v2/src/main/java/com/clickhouse/client/api/internal/HttpAPIClientHelper.java
@@ -297,6 +297,7 @@ private HttpClientConnectionManager poolConnectionManager(LayeredConnectionSocke
         PoolingHttpClientConnectionManager phccm = connMgrBuilder.build();
         poolControl = phccm;
         if (metricsRegistry != null) {
+            connectionFactory.enableMetrics();
             try {
                 String mGroupName = ClientConfigProperties.METRICS_GROUP_NAME.getOrDefault(configuration);
                 Class<?> micrometerLoader = getClass().getClassLoader().loadClass("com.clickhouse.client.api.metrics.MicrometerLoader");
@@ -1380,9 +1381,19 @@ public MeteredManagedHttpClientConnectionFactory(Http1Config http1Config, CharCo
 
         ConcurrentLinkedQueue<Long> times = new ConcurrentLinkedQueue<>();
 
+        // Connection times are drained only by the metrics gauge (see getTime()), so they are recorded
+        // only when a metrics registry is attached. Otherwise the queue would grow with every new connection.
+        private volatile boolean metricsEnabled = false;
+
+        public void enableMetrics() {
+            this.metricsEnabled = true;
+        }
 
         @Override
         public ManagedHttpClientConnection createConnection(Socket socket) throws IOException {
+            if (!metricsEnabled) {
+                return super.createConnection(socket);
+            }
             long startT = System.currentTimeMillis();
             try {
                 return super.createConnection(socket);
diff --git a/client-v2/src/test/java/com/clickhouse/client/api/internal/MeteredConnectionFactoryTest.java b/client-v2/src/test/java/com/clickhouse/client/api/internal/MeteredConnectionFactoryTest.java
new file mode 100644
index 000000000..48bbc96a4
--- /dev/null
+++ b/client-v2/src/test/java/com/clickhouse/client/api/internal/MeteredConnectionFactoryTest.java
@@ -0,0 +1,38 @@
+package com.clickhouse.client.api.internal;
+
+import org.apache.hc.core5.http.config.CharCodingConfig;
+import org.apache.hc.core5.http.config.Http1Config;
+import org.apache.hc.core5.http.impl.io.DefaultHttpResponseParserFactory;
+import org.testng.Assert;
+import org.testng.annotations.Test;
+
+import java.net.Socket;
+
+public class MeteredConnectionFactoryTest {
+
+    private static HttpAPIClientHelper.MeteredManagedHttpClientConnectionFactory newFactory() {
+        return new HttpAPIClientHelper.MeteredManagedHttpClientConnectionFactory(
+                Http1Config.DEFAULT, CharCodingConfig.DEFAULT, DefaultHttpResponseParserFactory.INSTANCE);
+    }
+
+    @Test(groups = {"unit"})
+    public void testConnectionTimesNotRecordedWithoutMetrics() throws Exception {
+        HttpAPIClientHelper.MeteredManagedHttpClientConnectionFactory factory = newFactory();
+        for (int i = 0; i < 10; i++) {
+            factory.createConnection(new Socket());
+        }
+        Assert.assertEquals(factory.times.size(), 0, "Connection times must not accumulate when metrics are disabled");
+    }
+
+    @Test(groups = {"unit"})
+    public void testConnectionTimesRecordedAndDrainedWithMetrics() throws Exception {
+        HttpAPIClientHelper.MeteredManagedHttpClientConnectionFactory factory = newFactory();
+        factory.enableMetrics();
+        for (int i = 0; i < 10; i++) {
+            factory.createConnection(new Socket());
+        }
+        Assert.assertEquals(factory.times.size(), 10);
+        factory.getTime();
+        Assert.assertEquals(factory.times.size(), 0);
+    }
+}
diff --git a/history/latest/3253.md b/history/latest/3253.md
new file mode 100644
index 000000000..0c722a0c5
--- /dev/null
+++ b/history/latest/3253.md
@@ -0,0 +1,4 @@
+- **[client-v2]** Fixed a memory leak where every new pooled HTTP connection added one entry to an internal queue of
+  connection times that was only drained by the metrics gauge. Without a metrics registry the queue was never emptied
+  and grew for the lifetime of the client. Connection times are now recorded only when metrics are enabled. `jdbc-v2`
+  is affected as well because it uses `client-v2`. (https://github.com/ClickHouse/clickhouse-java/issues/3253)