From 15deaf7255a32717a7f15a35e0229ecd720318fe Mon Sep 17 00:00:00 2001
From: Anton Ivashkin <ianton@live.com>
Date: Thu, 5 Mar 2026 13:56:55 +0100
Subject: [PATCH 1/2] Allow cluster request with undefined cluster on secondary
 nodes

---
 src/TableFunctions/ITableFunctionCluster.h |  5 ++++-
 tests/integration/test_s3_cluster/test.py  | 25 +++++++++++++++++++++-
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/src/TableFunctions/ITableFunctionCluster.h b/src/TableFunctions/ITableFunctionCluster.h
index 975322d054b3..d40246452555 100644
--- a/src/TableFunctions/ITableFunctionCluster.h
+++ b/src/TableFunctions/ITableFunctionCluster.h
@@ -76,7 +76,10 @@ class ITableFunctionCluster : public Base
         /// Cluster name is always the first
         cluster_name = checkAndGetLiteralArgument<String>(args[0], "cluster_name");
 
-        if (!context->tryGetCluster(cluster_name))
+        /// Cluster resolving is not required for secondary query
+        const auto is_secondary_query = context->getClientInfo().query_kind == ClientInfo::QueryKind::SECONDARY_QUERY;
+
+        if (!is_secondary_query && !context->tryGetCluster(cluster_name))
             throw Exception(ErrorCodes::CLUSTER_DOESNT_EXIST, "Requested cluster '{}' not found", cluster_name);
 
         /// Just cut the first arg (cluster_name) and try to parse other table function arguments as is
diff --git a/tests/integration/test_s3_cluster/test.py b/tests/integration/test_s3_cluster/test.py
index d607f390ba3c..18f5f0609e94 100644
--- a/tests/integration/test_s3_cluster/test.py
+++ b/tests/integration/test_s3_cluster/test.py
@@ -94,7 +94,7 @@ def started_cluster():
         cluster = ClickHouseCluster(__file__)
         cluster.add_instance(
             "s0_0_0",
-            main_configs=["configs/cluster.xml", "configs/named_collections.xml"],
+            main_configs=["configs/cluster.xml", "configs/named_collections.xml", "configs/cluster1.xml"],
             user_configs=["configs/users.xml"],
             macros={"replica": "node1", "shard": "shard1"},
             with_minio=True,
@@ -1237,3 +1237,26 @@ def query_cycle():
     node_to_shutdown.start_clickhouse()
 
     assert errors == 0
+
+
+def test_cluster_undefined_on_secondary_nodes(started_cluster):
+    node = started_cluster.instances["s0_0_0"]
+
+    expected_result = node.query(
+        f"""
+        SELECT * from s3(
+            'http://minio1:9001/root/data/{{clickhouse,database}}/*', 'minio', '{minio_secret_key}', 'CSV',
+            'name String, value UInt32, polygon Array(Array(Tuple(Float64, Float64)))') ORDER BY (name, value, polygon)
+        """
+    )
+
+    result = node.query(
+        f"""
+        SELECT * from s3Cluster(
+            'undefined_cluster',
+            'http://minio1:9001/root/data/{{clickhouse,database}}/*', 'minio', '{minio_secret_key}', 'CSV',
+            'name String, value UInt32, polygon Array(Array(Tuple(Float64, Float64)))') ORDER BY (name, value, polygon)
+        """
+    )
+
+    assert result == expected_result

From ded9261650edb30c55ce6c1c0be647b5e5795a40 Mon Sep 17 00:00:00 2001
From: Anton Ivashkin <ianton@live.com>
Date: Thu, 5 Mar 2026 14:07:44 +0100
Subject: [PATCH 2/2] Fix test

---
 .../test_s3_cluster/configs/cluster1.xml         | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)
 create mode 100644 tests/integration/test_s3_cluster/configs/cluster1.xml

diff --git a/tests/integration/test_s3_cluster/configs/cluster1.xml b/tests/integration/test_s3_cluster/configs/cluster1.xml
new file mode 100644
index 000000000000..ce96069a070a
--- /dev/null
+++ b/tests/integration/test_s3_cluster/configs/cluster1.xml
@@ -0,0 +1,16 @@
+<clickhouse>
+    <remote_servers>
+    <undefined_cluster>
+        <shard>
+            <replica>
+                <host>s0_0_1</host>
+                <port>9000</port>
+            </replica>
+            <replica>
+                <host>s0_1_0</host>
+                <port>9000</port>
+            </replica>
+        </shard>
+    </undefined_cluster>
+    </remote_servers>
+</clickhouse>