Try handling unclosed sql connections by calling dispose on the engine before it is put back into the pool.

cdplib/db_migration/MigrationCleaning.py

@@ -58,8 +58,8 @@ class MigrationCleaning:
         self._mapping_path = mapping_path
         self._schema_paths = schema_paths
 
-        from cdplib.db_handlers.SQLHandler import SQLHandlerPool
-        self._sql_db = SQLHandlerPool(20)
+        from cdplib.db_handlers.SQLHandler import SQLHandler
+        self._sql_db = SQLHandler()
 
     def _assert_dataframe_input(self, data: pd.DataFrame):
         '''
@@ -221,13 +221,10 @@ class MigrationCleaning:
 
         data = data.copy(deep=True)
 
-        #db = self._sql_db.aquire()
-        from cdplib.db_handlers.SQLHandler import SQLHandler
-        db = SQLHandler()
+        db = self._sql_db
 
         if invalid_mask.sum() == 0:
 
-            #self._sql_db.release(db)
             return data
 
         data_inconsist = data.assign(reason=reason)\