[result][database] Set max varchar size to 155 to deal with MySQL brain damage. Closes #1748

celery/backends/database/models.py

@@ -28,7 +28,7 @@ class Task(ResultModelBase):
     id = sa.Column(sa.Integer, sa.Sequence('task_id_sequence'),
                    primary_key=True,
                    autoincrement=True)
-    task_id = sa.Column(sa.String(255), unique=True)
+    task_id = sa.Column(sa.String(155), unique=True)
     status = sa.Column(sa.String(50), default=states.PENDING)
     result = sa.Column(PickleType, nullable=True)
     date_done = sa.Column(sa.DateTime, default=datetime.utcnow,
@@ -56,7 +56,7 @@ class TaskSet(ResultModelBase):
 
     id = sa.Column(sa.Integer, sa.Sequence('taskset_id_sequence'),
                    autoincrement=True, primary_key=True)
-    taskset_id = sa.Column(sa.String(255), unique=True)
+    taskset_id = sa.Column(sa.String(155), unique=True)
     result = sa.Column(PickleType, nullable=True)
     date_done = sa.Column(sa.DateTime, default=datetime.utcnow,
                           nullable=True)