Remove cancelQuery from processCancel to avoid killing unrelated pipelines

Algunenano · claude · Algunenano · commit 9fb0d3a03ce7 · 2026-03-20T20:11:24.000+01:00
The `cancelQuery` call on the `ProcessListElement` was too aggressive: it
cancels ALL registered pipeline executors, not just the one that received
the Cancel packet. This breaks parallel replica queries where multiple
executors share the same `ProcessListElement`.

Cancellation of scalar subqueries still works correctly: `processCancel`
throws `QUERY_WAS_CANCELLED_BY_CLIENT`, which propagates through the
cancel callback up through the pull loop.

Co-Authored-By: Claude Opus 4.6 (1M context) &lt;noreply@anthropic.com&gt;
diff --git a/src/Server/TCPHandler.cpp b/src/Server/TCPHandler.cpp
@@ -30,7 +30,6 @@
 #include <Interpreters/TablesStatus.h>
 #include <Interpreters/executeQuery.h>
 #include <Interpreters/Context.h>
-#include <Interpreters/ProcessList.h>
 #include <Parsers/ASTCreateQuery.h>
 #include <Parsers/ASTInsertQuery.h>
 #include <Server/TCPServer.h>
@@ -2712,14 +2711,6 @@ void TCPHandler::processCancel(QueryState & state)
     state.read_all_data = true;
     state.stop_query = true;
 
-    /// Cancel through the ProcessListElement so that all pipelines (including those
-    /// running during analysis, e.g. scalar subqueries) see the cancellation.
-    if (state.query_context)
-    {
-        if (auto process_list_element = state.query_context->getProcessListElement())
-            process_list_element->cancelQuery(CancelReason::CANCELLED_BY_USER);
-    }
-
     throw Exception(ErrorCodes::QUERY_WAS_CANCELLED_BY_CLIENT, "Received 'Cancel' packet from the client, canceling the query.");
 }
 
