Copilot commented on code in PR #17177:
URL: https://github.com/apache/pinot/pull/17177#discussion_r2618392546


##########
pinot-common/src/main/java/org/apache/pinot/common/utils/request/QueryFingerprintVisitor.java:
##########
@@ -0,0 +1,307 @@
+/**
+ * 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.pinot.common.utils.request;
+
+import java.util.ArrayList;
+import java.util.List;
+import javax.annotation.Nullable;
+import org.apache.calcite.sql.SqlCall;
+import org.apache.calcite.sql.SqlDynamicParam;
+import org.apache.calcite.sql.SqlJoin;
+import org.apache.calcite.sql.SqlLiteral;
+import org.apache.calcite.sql.SqlNode;
+import org.apache.calcite.sql.SqlNodeList;
+import org.apache.calcite.sql.SqlOrderBy;
+import org.apache.calcite.sql.SqlSelect;
+import org.apache.calcite.sql.SqlWith;
+import org.apache.calcite.sql.SqlWithItem;
+import org.apache.calcite.sql.fun.SqlCase;
+import org.apache.calcite.sql.type.SqlTypeName;
+import org.apache.calcite.sql.util.SqlShuttle;
+
+
+/**
+ * QueryFingerprintVisitor traverses the Calcite SqlNode AST and produces a 
normalized query fingerprint.
+ * Implementation is based on Calcite 1.40.0 version. It may change in future 
versions of Calcite.
+ *
+ * <p>
+ * <ul>
+ *   <li>All data literals are replaced with dynamic parameters (?)</li>
+ *   <li>IN/NOT IN clauses with multiple constants are squashed to a single 
parameter.</li>
+ *   <li>EXPLAIN PLAN FOR is NOT preserved.</li>
+ *   <li>Symbolic keywords (DISTINCT, ASC, DESC, etc.) and NULL literals are 
preserved.</li>
+ *   <li>Hints are preserved.</li>
+ *   <li>Window functions: window specification (operand 1) are preserved.</li>
+ * </ul>
+ * </p>
+ */
+public class QueryFingerprintVisitor extends SqlShuttle {
+  // SqlSelect operand index for hints, see {@link 
org.apache.calcite.sql.SqlSelect}.
+  private static final int SQLSELECT_HINTS_OPERAND_INDEX = 11;
+
+  // SqlJoin operand indices, see {@link org.apache.calcite.sql.SqlJoin}.
+  private static final int SQLJOIN_NATURAL_OPERAND_INDEX = 1;
+  private static final int SQLJOIN_JOIN_TYPE_OPERAND_INDEX = 2;
+  private static final int SQLJOIN_CONDITION_TYPE_OPERAND_INDEX = 4;
+
+  private int _dynamicParamIndex = 0;
+
+  @Override

Review Comment:
   The `_dynamicParamIndex` field is never reset between query fingerprints. If 
the same visitor instance is reused for multiple queries, the dynamic parameter 
indices will continue incrementing. Consider either documenting that each 
visitor instance should only be used once, or resetting `_dynamicParamIndex` at 
the start of the visit process.
   ```suggestion
     @Override
     public SqlNode visit(SqlNode node) {
       _dynamicParamIndex = 0;
       return super.visit(node);
     }
   
     @Override
   ```



##########
pinot-broker/src/main/java/org/apache/pinot/broker/requesthandler/MultiStageBrokerRequestHandler.java:
##########
@@ -311,11 +331,11 @@ protected BrokerResponse handleRequestThrowing(long 
requestId, String query, Sql
 
     QueryExecutionContext executionContext =
         new QueryExecutionContext(QueryExecutionContext.QueryType.MSE, 
requestId, cid, workloadName, startTimeMs,
-            activeDeadlineMs, passiveDeadlineMs, _brokerId, _brokerId);
+            activeDeadlineMs, passiveDeadlineMs, _brokerId, _brokerId, 
queryHash);
     QueryThreadContext.MseWorkerInfo mseWorkerInfo = new 
QueryThreadContext.MseWorkerInfo(0, 0);
     try (QueryThreadContext ignore = QueryThreadContext.open(executionContext, 
mseWorkerInfo, _threadAccountant);

Review Comment:
   The queryHash registered in MDC at line 313 is never unregistered after the 
request completes. This creates a resource leak where MDC entries accumulate. 
Since QueryThreadContext is responsible for MDC cleanup (as seen in its close() 
method), and executionContext now contains the queryHash, the MDC registration 
should occur inside the try-with-resources block where QueryThreadContext.open 
is called, not before it.



##########
pinot-broker/src/main/java/org/apache/pinot/broker/requesthandler/BaseSingleStageBrokerRequestHandler.java:
##########
@@ -340,7 +359,8 @@ protected BrokerResponse handleRequest(long requestId, 
String query, SqlNodeAndO
     // TODO: Revisit whether we should set deadline here
     QueryExecutionContext executionContext =
         new QueryExecutionContext(QueryExecutionContext.QueryType.SSE, 
requestId, cid, workloadName,
-            requestContext.getRequestArrivalTimeMillis(), Long.MAX_VALUE, 
Long.MAX_VALUE, _brokerId, _brokerId);
+            requestContext.getRequestArrivalTimeMillis(), Long.MAX_VALUE, 
Long.MAX_VALUE, _brokerId, _brokerId,
+            queryHash);
     try (QueryThreadContext ignore = QueryThreadContext.open(executionContext, 
_threadAccountant)) {

Review Comment:
   The queryHash registered in MDC at line 344 is never unregistered after the 
request completes. This creates a resource leak where MDC entries accumulate. 
Since QueryThreadContext is responsible for MDC cleanup (as seen in its close() 
method), and executionContext now contains the queryHash, the MDC registration 
should occur inside the try-with-resources block where QueryThreadContext.open 
is called, not before it.



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