changes in connection

datajoint/connection.py

@@ -2,7 +2,7 @@
 This module hosts the Connection class that manages the connection to the mysql database,
  and the `conn` function that provides access to a persistent connection in datajoint.
 """
-
+import warnings
 from contextlib import contextmanager
 import pymysql as client
 import logging
@@ -59,7 +59,7 @@ def __init__(self, host, user, passwd, init_fun=None):
             port = int(port)
         else:
             port = config['database.port']
-        self.conn_info = dict(host=host, port=port, user=user, passwd=passwd)
+        self.conn_info = dict(host=host, port=port, user=user, passwd=passwd, max_allowed_packet=1024**3) # 1073741824
         self._conn = client.connect(init_command=init_fun, **self.conn_info)
         if self.is_connected:
             logger.info("Connected {user}@{host}:{port}".format(**self.conn_info))
@@ -161,19 +161,25 @@ def commit_transaction(self):
     def transaction(self):
         """
         Context manager for transactions. Opens an transaction and closes it after the with statement.
-        If an error is caught during the transaction, the commits are automatically rolled back. All
-        errors are raised again.
+        Only starts a transaction if there is not one going on already (MySQL does not support nested
+        transactions). If an error is caught during the transaction, the commits are automatically
+        rolled back. All errors are raised again.
 
         Example:
         >>> import datajoint as dj
         >>> with dj.conn().transaction as conn:
         >>>     # transaction is open here
         """
-        try:
-            self.start_transaction()
-            yield self
-        except:
-            self.cancel_transaction()
-            raise
+        if not self.in_transaction:
+            try:
+                self.start_transaction()
+                yield self
+            except:
+                self.cancel_transaction()
+                raise
+            else:
+                self.commit_transaction()
         else:
-            self.commit_transaction()
+            warnings.warn("""Connection is in a transaction already. MySQL does not support nested transaction. This
+                        transaction call will be ignored. """)
+            yield self