Merge pull request #22235 from ClickHouse/quantile-deterministic-msan

Fix MSan report in `quantileDeterministic`

src/AggregateFunctions/ReservoirSamplerDeterministic.h

@@ -13,6 +13,7 @@
 #include <Common/NaNUtils.h>
 #include <Poco/Exception.h>
 
+
 namespace DB
 {
 namespace ErrorCodes
@@ -162,6 +163,11 @@ public:
         sorted = false;
     }
 
+#if !__clang__
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wclass-memaccess"
+#endif
+
     void write(DB::WriteBuffer & buf) const
     {
         size_t size = samples.size();
@@ -169,9 +175,26 @@ public:
         DB::writeIntBinary<size_t>(total_values, buf);
 
         for (size_t i = 0; i < size; ++i)
-            DB::writePODBinary(samples[i], buf);
+        {
+            /// There was a mistake in this function.
+            /// Instead of correctly serializing the elements,
+            ///  it was writing them with uninitialized padding.
+            /// Here we ensure that padding is zero without changing the protocol.
+            /// TODO: After implementation of "versioning aggregate function state",
+            /// change the serialization format.
+
+            Element elem;
+            memset(&elem, 0, sizeof(elem));
+            elem = samples[i];
+
+            DB::writePODBinary(elem, buf);
+        }
     }
 
+#if !__clang__
+#pragma GCC diagnostic pop
+#endif
+
 private:
     /// We allocate some memory on the stack to avoid allocations when there are many objects with a small number of elements.
     using Element = std::pair<T, UInt32>;

tests/queries/0_stateless/01779_quantile_deterministic_msan.reference

+11447494982455782708

tests/queries/0_stateless/01779_quantile_deterministic_msan.sql

+SELECT cityHash64(toString(quantileDeterministicState(number, sipHash64(number)))) FROM numbers(8193);