Add final to some classes

src/IO/WriteBufferFromArena.h

@@ -13,7 +13,7 @@ namespace DB
   *
   * While using this object, no other allocations in arena are possible.
   */
-class WriteBufferFromArena : public WriteBuffer
+class WriteBufferFromArena final : public WriteBuffer
 {
 private:
     Arena & arena;

src/Interpreters/DDLWorker.cpp

@@ -1203,7 +1203,7 @@ void DDLWorker::runCleanupThread()
 }
 
 
-class DDLQueryStatusInputStream : public IBlockInputStream
+class DDLQueryStatusInputStream final : public IBlockInputStream
 {
 public:
 

src/Interpreters/InterpreterKillQueryQuery.h

@@ -12,7 +12,7 @@ class Context;
 class AccessRightsElements;
 
 
-class InterpreterKillQueryQuery : public IInterpreter
+class InterpreterKillQueryQuery final : public IInterpreter
 {
 public:
     InterpreterKillQueryQuery(const ASTPtr & query_ptr_, Context & context_)