Add dangerous join condition watchdog to prevent Cartesian and oversi…

README.md

@@ -109,6 +109,10 @@ and others would not be possible without your help.
 
 Ready? [Getting Started](https://kyuubi.readthedocs.io/en/master/quick_start/) with Kyuubi.
 
+## Security & Guard
+
+- [Dangerous Join Watchdog](./docs/watchdog/dangerous-join.md)
+
 ## [Contributing](./CONTRIBUTING.md)
 
 ## Project & Community Status

docs/configuration/settings.md

@@ -580,6 +580,18 @@ jdbc:hive2://localhost:10009/default;#spark.sql.shuffle.partitions=2;spark.execu
 
 Please refer to the Spark official online documentation for [SET Command](https://spark.apache.org/docs/latest/sql-ref-syntax-aux-conf-mgmt-set.html)
 
+### Dangerous Join Watchdog
+
+You can enable dangerous join detection for Spark SQL extension with:
+
+|                      Name                      | Default |                                    Description                                     |
+|------------------------------------------------|---------|------------------------------------------------------------------------------------|
+| `kyuubi.watchdog.dangerousJoin.enabled`        | `false` | Enable dangerous join detection                                                    |
+| `kyuubi.watchdog.dangerousJoin.broadcastRatio` | `0.8`   | Ratio against Spark broadcast threshold to identify oversized broadcast fallback   |
+| `kyuubi.watchdog.dangerousJoin.action`         | `WARN`  | `WARN` logs warning diagnostics, `REJECT` throws exception with error code `41101` |
+
+Please see [Dangerous Join Watchdog](../watchdog/dangerous-join.md) for rules and examples.
+
 ## Flink Configurations
 
 ### Via flink-conf.yaml

docs/deployment/index.rst

@@ -27,6 +27,7 @@ Basics
     :glob:
 
     kyuubi_on_kubernetes
+    settings
     hive_metastore
     high_availability_guide
     migration-guide
@@ -42,4 +43,4 @@ Engines
     engine_on_kubernetes
     engine_share_level
     engine_lifecycle
-    spark/index
+    spark/index

docs/deployment/settings.md

@@ -0,0 +1,34 @@
+<!--
+- 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.
+-->
+
+# Deployment Settings for Dangerous Join Watchdog
+
+## Spark SQL Extensions
+
+```properties
+spark.sql.extensions=org.apache.kyuubi.sql.KyuubiSparkSQLExtension,org.apache.kyuubi.sql.watchdog.KyuubiDangerousJoinExtension
+```
+
+## Dangerous Join Configurations
+
+|                      Name                      | Default |                        Description                        |
+|------------------------------------------------|---------|-----------------------------------------------------------|
+| `kyuubi.watchdog.dangerousJoin.enabled`        | `false` | Enable dangerous join watchdog                            |
+| `kyuubi.watchdog.dangerousJoin.broadcastRatio` | `0.8`   | Broadcast threshold coefficient                           |
+| `kyuubi.watchdog.dangerousJoin.action`         | `WARN`  | `WARN` only logs diagnostics, `REJECT` throws error 41101 |
+
+For detailed rules and examples, see [Dangerous Join Watchdog](../watchdog/dangerous-join.md).

docs/index.rst

@@ -181,6 +181,7 @@ What's Next
 
    quick_start/index
    configuration/settings
+   watchdog/dangerous-join
    deployment/index
    Security <security/index>
    monitor/index

docs/watchdog/dangerous-join.md

@@ -0,0 +1,105 @@
+<!--
+- 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.
+-->
+
+# Dangerous Join Watchdog
+
+Kyuubi Dangerous Join Watchdog detects risky join planning patterns before query execution.
+It helps reduce accidental Cartesian products, oversized broadcast attempts, and long-running nested loop joins.
+
+## Background
+
+In shared SQL gateway environments, a single risky join can consume excessive driver memory or create very slow jobs.
+The Dangerous Join Watchdog adds planning-time checks for these high-risk patterns.
+
+## Risk Rules
+
+### Equi-Join
+
+- Rule 1: Equi-join is marked dangerous when it degrades to a Cartesian pattern.
+- Rule 2: Equi-join is marked dangerous when the estimated build side exceeds the configured broadcast ratio threshold.
+
+### Non-Equi Join
+
+- Rule 1: Non-equi join is marked dangerous when both sides exceed broadcast threshold and effectively become Cartesian risk.
+- Rule 2: Non-equi join is marked dangerous when build side is not selectable and the plan falls back to a second BNLJ pattern.
+
+## Configurations
+
+|                      Name                      | Default |                                  Meaning                                  |
+|------------------------------------------------|---------|---------------------------------------------------------------------------|
+| `kyuubi.watchdog.dangerousJoin.enabled`        | `false` | Enable or disable dangerous join detection                                |
+| `kyuubi.watchdog.dangerousJoin.broadcastRatio` | `0.8`   | Ratio against Spark broadcast threshold for warning/reject decision       |
+| `kyuubi.watchdog.dangerousJoin.action`         | `WARN`  | `WARN` logs diagnostics; `REJECT` throws exception and rejects submission |
+
+## Usage
+
+1. Put Kyuubi Spark extension jar into Spark classpath.
+2. Configure SQL extensions:
+
+```properties
+spark.sql.extensions=org.apache.kyuubi.sql.KyuubiSparkSQLExtension,org.apache.kyuubi.sql.watchdog.KyuubiDangerousJoinExtension
+```
+
+3. Configure action:
+
+```properties
+kyuubi.watchdog.dangerousJoin.action=WARN
+```
+
+or
+
+```properties
+kyuubi.watchdog.dangerousJoin.action=REJECT
+```
+
+## Sample WARN Log
+
+When action is `WARN`, Kyuubi writes a structured JSON payload:
+
+```text
+KYUUBI_LOG_KEY={"sql":"SELECT ...","joinType":"INNER","reason":"Cartesian","leftSize":10485760,"rightSize":15728640,"broadcastThreshold":10485760,"broadcastRatio":0.8}
+```
+
+## Sample REJECT Error
+
+When action is `REJECT`, query submission fails with:
+
+```text
+errorCode=41101
+Query rejected due to dangerous join strategy: {...details...}
+```
+
+## Disable or Tune
+
+- Disable watchdog:
+
+```properties
+kyuubi.watchdog.dangerousJoin.enabled=false
+```
+
+- Increase tolerance:
+
+```properties
+kyuubi.watchdog.dangerousJoin.broadcastRatio=0.95
+```
+
+## FAQ
+
+### What if `spark.sql.adaptive.enabled=true`?
+
+Dangerous Join Watchdog runs in planner strategy phase and evaluates pre-execution plan statistics.
+AQE may still optimize runtime plans, but watchdog decisions are made before query execution starts.

extensions/spark/kyuubi-extension-spark-3-3/src/main/scala/org/apache/kyuubi/sql/KyuubiSQLConf.scala

@@ -123,6 +123,30 @@ object KyuubiSQLConf {
       .bytesConf(ByteUnit.BYTE)
       .createOptional
 
+  val DANGEROUS_JOIN_ENABLED =
+    buildConf("kyuubi.watchdog.dangerousJoin.enabled")
+      .doc("Enable dangerous join condition detection.")
+      .version("1.11.0")
+      .booleanConf
+      .createWithDefault(false)
+
+  val DANGEROUS_JOIN_BROADCAST_RATIO =
+    buildConf("kyuubi.watchdog.dangerousJoin.broadcastRatio")
+      .doc("The threshold ratio to mark oversized broadcast fallback.")
+      .version("1.11.0")
+      .doubleConf
+      .checkValue(v => v > 0 && v <= 1, "must be in (0, 1]")
+      .createWithDefault(0.8)
+
+  val DANGEROUS_JOIN_ACTION =
+    buildConf("kyuubi.watchdog.dangerousJoin.action")
+      .doc("Action when dangerous join is detected, one of WARN and REJECT.")
+      .version("1.11.0")
+      .stringConf
+      .transform(_.toUpperCase(java.util.Locale.ROOT))
+      .checkValues(Set("WARN", "REJECT"))
+      .createWithDefault("WARN")
+
   val DROP_IGNORE_NONEXISTENT =
     buildConf("spark.sql.optimizer.dropIgnoreNonExistent")
       .doc("Do not report an error if DROP DATABASE/TABLE/VIEW/FUNCTION/PARTITION specifies " +

extensions/spark/kyuubi-extension-spark-3-3/src/main/scala/org/apache/kyuubi/sql/KyuubiSparkSQLExtension.scala

@@ -19,7 +19,7 @@ package org.apache.kyuubi.sql
 
 import org.apache.spark.sql.{FinalStageResourceManager, InjectCustomResourceProfile, SparkSessionExtensions}
 
-import org.apache.kyuubi.sql.watchdog.{KyuubiUnsupportedOperationsCheck, MaxScanStrategy}
+import org.apache.kyuubi.sql.watchdog.{DangerousJoinInterceptor, KyuubiUnsupportedOperationsCheck, MaxScanStrategy}
 
 // scalastyle:off line.size.limit
 /**
@@ -39,6 +39,7 @@ class KyuubiSparkSQLExtension extends (SparkSessionExtensions => Unit) {
     // watchdog extension
     extensions.injectCheckRule(_ => KyuubiUnsupportedOperationsCheck)
     extensions.injectPlannerStrategy(MaxScanStrategy)
+    extensions.injectPlannerStrategy(DangerousJoinInterceptor(_))
 
     extensions.injectQueryStagePrepRule(FinalStageResourceManager(_))
     extensions.injectQueryStagePrepRule(InjectCustomResourceProfile)

extensions/spark/kyuubi-extension-spark-3-3/src/main/scala/org/apache/kyuubi/sql/watchdog/DangerousJoinCounter.scala

@@ -0,0 +1,80 @@
+/*
+ * 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.kyuubi.sql.watchdog
+
+import scala.collection.mutable.ArrayBuffer
+
+object DangerousJoinCounter {
+  case class Entry(
+      sqlText: String,
+      joinType: String,
+      reason: String,
+      leftSize: BigInt,
+      rightSize: BigInt,
+      broadcastThreshold: Long,
+      broadcastRatio: Double) {
+    def toJson: String = {
+      val pairs = Seq(
+        "sql" -> escape(sqlText),
+        "joinType" -> escape(joinType),
+        "reason" -> escape(reason),
+        "leftSize" -> leftSize.toString,
+        "rightSize" -> rightSize.toString,
+        "broadcastThreshold" -> broadcastThreshold.toString,
+        "broadcastRatio" -> broadcastRatio.toString)
+      pairs.map { case (k, v) =>
+        if (k == "leftSize" || k == "rightSize" || k == "broadcastThreshold" || k == "broadcastRatio") {
+          s""""$k":$v"""
+        } else {
+          s""""$k":"$v""""
+        }
+      }.mkString("{", ",", "}")
+    }
+  }
+
+  private val entries = ArrayBuffer.empty[Entry]
+
+  def add(entry: Entry): Unit = synchronized {
+    entries += entry
+  }
+
+  def count: Int = synchronized {
+    entries.size
+  }
+
+  def latest: Option[Entry] = synchronized {
+    entries.lastOption
+  }
+
+  def snapshot: Seq[Entry] = synchronized {
+    entries.toSeq
+  }
+
+  def reset(): Unit = synchronized {
+    entries.clear()
+  }
+
+  private def escape(raw: String): String = {
+    raw
+      .replace("\\", "\\\\")
+      .replace("\"", "\\\"")
+      .replace("\n", "\\n")
+      .replace("\r", "\\r")
+      .replace("\t", "\\t")
+  }
+}