use server max_allowed_packet with limit for memory save.

WorldException · WorldException · commit c3e0f2f40e6f · 2016-02-24T12:13:08.000+03:00
diff --git a/pymysql/connections.py b/pymysql/connections.py
@@ -902,6 +902,9 @@ def connect(self, sock=None):
             self._get_server_information()
             self._request_authentication()
 
+            self.max_allowed_packet = min(self.max_allowed_packet,
+                                          self.get_system_variable('max_allowed_packet', self.max_allowed_packet))
+
             if self.sql_mode is not None:
                 c = self.cursor()
                 c.execute("SET sql_mode=%s", (self.sql_mode,))
diff --git a/pymysql/cursors.py b/pymysql/cursors.py
@@ -25,7 +25,7 @@ class Cursor(object):
     #:
     #: Max size of allowed statement is max_allowed_packet - packet_header_size.
     #: Default value of max_allowed_packet is 1048576.
-    max_stmt_length = 1024000
+    max_stmt_length = 1024000 * 6
     packet_header_size = 4
 
     def __init__(self, connection):
@@ -41,6 +41,7 @@ def __init__(self, connection):
         self._executed = None
         self._result = None
         self._rows = None
+        self.max_stmt_length = min(Cursor.max_stmt_length, connection.max_allowed_packet - Cursor.packet_header_size)
 
     def close(self):
         '''
@@ -159,8 +160,6 @@ def executemany(self, query, args):
 
         m = RE_INSERT_VALUES.match(query)
         if m:
-            if self.max_stmt_length == Cursor.max_stmt_length:
-                self.max_stmt_length = self.connection.get_system_variable("max_allowed_packet") - self.packet_header_size
             q_prefix = m.group(1)
             q_values = m.group(2).rstrip()
             q_postfix = m.group(3) or ''
