Question

I’ve created an app on appengine, but am running into an issue. It seems to me that the PersistenceManagerFactory is creating a new connection to the datastore on each request. It is common for my datastore reads to take 4 to 5 seconds for only about 10 objects! (Its a get all entity level query).

After looking at appstats, it looks like the requests are sitting there for about 3 seconds before making the call to the datastore. The actual datastore time is small, 4-10ms.

I then changed my get all query to use the low level DatastoreService api. I create the service once, and use it in the get all method. This pretty much erased the wait time (except for the first time the method is called). So I’m guessing that the PMF is getting a new connection to the datastore for each read! This seems crazy.

Does anyone know how to minimize the spin up time of a PersistenceManager instance?
jdoconfig.xml

   <persistence-manager-factory name="transactions-optional">
       <property name="javax.jdo.PersistenceManagerFactoryClass"
           value="org.datanucleus.api.jdo.JDOPersistenceManagerFactory"/>
       <property name="javax.jdo.option.ConnectionURL" value="appengine"/>
       <property name="javax.jdo.option.NontransactionalRead" value="true"/>
       <property name="javax.jdo.option.NontransactionalWrite" value="true"/>
       <property name="javax.jdo.option.RetainValues" value="true"/>
       <property name="datanucleus.appengine.autoCreateDatastoreTxns" value="true"/>
       <property name="datanucleus.appengine.singletonPMFForName" value="true"/>
   </persistence-manager-factory>

getAll method (using jdo)

    @Override
    public ArrayList<CrudObject> getAll(String className) {
        List results = null;
        PersistenceManager pm = pmf.getPersistenceManager();
        try{
            Query q = pm.newQuery(Class.forName(className));
            results = (List)q.execute();
            return new ArrayList<CrudObject>(pm.detachCopyAll(results));
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }finally
        {
            pm.close();
        }
        return null;
      }

Answer 1

The issue was due to a latency issue on the AppEngine Datastore platform. The issue was temporary, and has been fixed. The issue just happened to coincide with my first deploy to AppEngine using JDO, so I figured it was my code. I retested today, and it is running much faster.