Question

I have a functioning recommender that I wanted to make faster so I decided to connect it directly to my database. However, every time I try to recommend things to people I get an error that setFetchSize() is not >=0. Here is my code:

MySQLJDBCDataModel dataModel = null;
try {
  Class.forName("net.sourceforge.jtds.jdbc.Driver");
  net.sourceforge.jtds.jdbcx.JtdsDataSource ds = new net.sourceforge.jtds.jdbcx.JtdsDataSource();
  ds.setServerName("xxxxx");
  ds.setDatabaseName("xxxxx");
  ds.setUser("xxxxx");
  ds.setPassword(xxxxx);
  ds.setDomain("xxxxx");
  //net.sourceforge.jtds.jdbc.JtdsStatement.setFetchSize(10);
  dataModel = new MySQLJDBCDataModel(ds, "test_tbl", "user_id", "item_id", "preference", null);
} catch (Exception e) {
  System.out.println("can't connect");
}
ArrayList<String> itemList=new ArrayList<String>();
ItemSimilarity similarity = new FileItemSimilarity(new File("output/part-r-00000"));
ItemBasedRecommender recommender = new GenericItemBasedRecommender(dataModel, similarity);
//List<RecommendedItem> recommendedItems=recommender.recommend(userid,10);
Recommender cachingRecommender = new CachingRecommender(recommender);
List<userRecData> allUserRecs = new ArrayList<userRecData>();
List<RecommendedItem> uRec=cachingRecommender.recommend(userobjectid,10);

And I get the error:

java.sql.SQLException: The setFetchSize method requires a parameter value >= 0.
at net.sourceforge.jtds.jdbc.JtdsStatement.setFetchSize(JtdsStatement.java:998)
at org.apache.mahout.cf.taste.impl.model.jdbc.AbstractJDBCDataModel.getNumThings(AbstractJDBCDataModel.java:584)
at org.apache.mahout.cf.taste.impl.model.jdbc.AbstractJDBCDataModel.getNumUsers(AbstractJDBCDataModel.java:560)
at org.apache.mahout.cf.taste.impl.recommender.CachingRecommender.<init>(CachingRecommender.java:63)
at mia.recommender.RecommenderIntro.getRecommendations(RecommenderIntro.java:79)
at mia.recommender.RecommenderIntro.main(RecommenderIntro.java:43)

It fails on the cachingRecommender, or if I take that out, on recommnder.recommend
I thought that Mahout automatically set the fetch size to 1000

Answer 1

You’re using MySQLJDBCDataModel, but your database is SQL Server. The MySQL implementation disables fetch size with a negative value because its driver needs that. You need to customize AbstractJDBCDataModel to work with SQL Server — by not overriding getFetchSize() for example.