diff --git a/dbms/include/DB/Interpreters/ProcessList.h b/dbms/include/DB/Interpreters/ProcessList.h
index b1240806b37..a49773cd3b4 100644
--- a/dbms/include/DB/Interpreters/ProcessList.h
+++ b/dbms/include/DB/Interpreters/ProcessList.h
@@ -84,8 +84,9 @@ protected:
 	BlockInputStreamPtr query_stream_in;
 	BlockOutputStreamPtr query_stream_out;
 
-	/// Abovemetioned streams haved delayed initialization, use this flag to track initialization
-	/// Can be set to true by single thread, can be read from multiple
+	/// Abovemetioned streams have delayed initialization, this flag indicates thier initialization
+	/// It is better to use atomic (instead of raw bool) with tryGet/setQueryStreams() thread-safe methods despite that
+	///  now in all contexts ProcessListElement is always used under ProcessList::mutex (and raw bool is also Ok)
 	std::atomic<bool> query_streams_initialized{false};
 
 public:
@@ -146,7 +147,7 @@ public:
 		return res;
 	}
 
-	/// Copies pointers to in/out streams
+	/// Copies pointers to in/out streams, it can be called once
 	void setQueryStreams(const BlockIO & io);
 	/// Get query in/out pointers
 	bool tryGetQueryStreams(BlockInputStreamPtr & in, BlockOutputStreamPtr & out) const;
@@ -264,13 +265,13 @@ public:
 	{
 		NotFound = 0, 					/// already cancelled
 		QueryIsNotInitializedYet = 1,
-		CancelCannotBeSended = 2,
-		CancelSended = 3,
+		CancelCannotBeSent = 2,
+		CancelSent = 3,
 		Unknown
 	};
 
 	/// Try call cancel() for input and output streams of query with specified id and user
-	CancellationCode sendCancelToQuery(const String & query_id, const String & intial_user);
+	CancellationCode sendCancelToQuery(const String & current_query_id, const String & current_user);
 };
 
 }
diff --git a/dbms/include/DB/Parsers/ASTKillQueryQuery.h b/dbms/include/DB/Parsers/ASTKillQueryQuery.h
index d1fd43d7500..bd318ac56c9 100644
--- a/dbms/include/DB/Parsers/ASTKillQueryQuery.h
+++ b/dbms/include/DB/Parsers/ASTKillQueryQuery.h
@@ -7,9 +7,9 @@ namespace DB
 class ASTKillQueryQuery : public ASTQueryWithOutput
 {
 public:
-	ASTPtr where_expression;
-	bool sync = false;
-	bool test = false;
+	ASTPtr where_expression;	// expression to filter processes from system.processes table
+	bool sync = false;			// SYNC or ASYNC mode
+	bool test = false;			// does it TEST mode? (doesn't cancel queries just checks and shows them)
 
 	ASTKillQueryQuery() = default;
 
diff --git a/dbms/src/Interpreters/InterpreterKillQueryQuery.cpp b/dbms/src/Interpreters/InterpreterKillQueryQuery.cpp
index 1bdcdd4b38b..bd28bcdf9c0 100644
--- a/dbms/src/Interpreters/InterpreterKillQueryQuery.cpp
+++ b/dbms/src/Interpreters/InterpreterKillQueryQuery.cpp
@@ -32,9 +32,9 @@ static const char * cancellationCodeToStatus(CancellationCode code)
 			return "finished";
 		case CancellationCode::QueryIsNotInitializedYet:
 			return "pending";
-		case CancellationCode::CancelCannotBeSended:
+		case CancellationCode::CancelCannotBeSent:
 			return "error";
-		case CancellationCode::CancelSended:
+		case CancellationCode::CancelSent:
 			return "waiting";
 		default:
 			return "unknown_status";
@@ -141,13 +141,13 @@ public:
 
 				auto code = process_list.sendCancelToQuery(curr_process.query_id, curr_process.user);
 
-				if (code != CancellationCode::QueryIsNotInitializedYet && code != CancellationCode::CancelSended)
+				if (code != CancellationCode::QueryIsNotInitializedYet && code != CancellationCode::CancelSent)
 				{
 					curr_process.processed = true;
 					insertResultRow(curr_process.source_num, code, processes_block, res);
 					++num_processed_queries;
 				}
-				/// Wait if QueryIsNotInitializedYet or CancelSended
+				/// Wait if QueryIsNotInitializedYet or CancelSent
 			}
 
 			/// KILL QUERY could be killed also
diff --git a/dbms/src/Interpreters/ProcessList.cpp b/dbms/src/Interpreters/ProcessList.cpp
index 2b1cc75222a..a8d0c054758 100644
--- a/dbms/src/Interpreters/ProcessList.cpp
+++ b/dbms/src/Interpreters/ProcessList.cpp
@@ -20,7 +20,7 @@ ProcessList::EntryPtr ProcessList::insert(
 	const String & query_, const IAST * ast, const ClientInfo & client_info, const Settings & settings)
 {
 	EntryPtr res;
-	bool is_kill_query = ast && dynamic_cast<const ASTKillQueryQuery *>(ast);
+	bool is_kill_query = ast && typeid_cast<const ASTKillQueryQuery *>(ast);
 
 	{
 		std::lock_guard<std::mutex> lock(mutex);
@@ -151,7 +151,7 @@ void ProcessListElement::setQueryStreams(const BlockIO & io)
 {
 	query_stream_in = io.in;
 	query_stream_out = io.out;
-	query_streams_initialized = true;
+	query_streams_initialized = true; // forces strict memory ordering
 }
 
 bool ProcessListElement::tryGetQueryStreams(BlockInputStreamPtr & in, BlockOutputStreamPtr & out) const
@@ -229,9 +229,9 @@ ProcessList::CancellationCode ProcessList::sendCancelToQuery(const String & curr
 		if (input_stream && (input_stream_casted = dynamic_cast<IProfilingBlockInputStream *>(input_stream.get())))
 		{
 			input_stream_casted->cancel();
-			return CancellationCode::CancelSended;
+			return CancellationCode::CancelSent;
 		}
-		return CancellationCode::CancelCannotBeSended;
+		return CancellationCode::CancelCannotBeSent;
 	}
 	return CancellationCode::QueryIsNotInitializedYet;
 }