Fix interleaved repo delete with RAC via a transaction

The RepositoryActionCount table can have entries added while a repository deletion is in progress. We now perform the repository deletion under a transaction and explicitly test for RAC entries in the deletion unit test (which doesn't test interleaving, but it was missing this check).

Fixes #494

data/database.py

@@ -119,6 +119,7 @@ db = Proxy()
 read_slave = Proxy()
 db_random_func = CallableProxy()
 db_for_update = CallableProxy()
+db_transaction = CallableProxy()
 
 
 def validate_database_url(url, db_kwargs, connect_timeout=5):
@@ -164,6 +165,10 @@ def configure(config_object):
   if read_slave_uri is not None:
     read_slave.initialize(_db_from_url(read_slave_uri, db_kwargs))
 
+  def _db_transaction():
+    return config_object['DB_TRANSACTION_FACTORY'](db)
+
+  db_transaction.initialize(_db_transaction)
 
 def random_string_generator(length=16):
   def random_string():
@@ -373,14 +378,15 @@ class Repository(BaseModel):
       return sorted_models.index(cmp_fk.model_class.__name__)
     filtered_ops.sort(key=sorted_model_key)
 
-    for query, fk in filtered_ops:
-      model = fk.model_class
-      if fk.null and not delete_nullable:
-        model.update(**{fk.name: None}).where(query).execute()
-      else:
-        model.delete().where(query).execute()
+    with db_transaction():
+      for query, fk in filtered_ops:
+        model = fk.model_class
+        if fk.null and not delete_nullable:
+          model.update(**{fk.name: None}).where(query).execute()
+        else:
+          model.delete().where(query).execute()
 
-    return self.delete().where(self._pk_expr()).execute()
+      return self.delete().where(self._pk_expr()).execute()
 
 class Star(BaseModel):
   user = ForeignKeyField(User, index=True)