JDBC plugin for Elasticsearch is not working properly

I'm using the elasticsearch 1.3.2 version which I installed the JDBC plugin river(version 1.3.4).
Once in while, the river stops working and I need to delete everything(index, river) and create again.
We normally alter the MySQL database. Does this influence on the river
plugin? Do I need to do something after every alter on database or can
be something else?

Thanks in advance.