Delaying AppEngine to DB latency temporarily ~ 10 seconds every ~ 20 calls?

This (see table below) happens from 3/7. Of course, this could be due to the download and upload of instances. But do you know other reasons why GAE behaves this way?

This is not a tall replication instance. And during testing, we had up to 5 instances of F2 working only with our test client calls. These are mainly DB calls, image processing and using memcache.

There are already 2 questions that look the same: http://code.google.com/p/googleappengine/issues/detail?id=4180&sort=priority&colspec=ID%20Type%20Component%20Status%20Stars%20Summary%20Language%20Priority%20Owner % 20Log

http://code.google.com/p/googleappengine/issues/detail?id=6309&sort=priority&colspec=ID%20Type%20Component%20Status%20Stars%20Summary%20Language%20Priority%20Owner%20Log

And here is the forum post: https://groups.google.com/forum/#!topic/google-appengine/js5CeRWLQZ0/discussion

The logging (as requested by Shay) shows that the Persistence Manager appears to take 6 seconds to initialize:

2012-03-11 15:32:47.543 /api/yyy 200 16811ms 0kb xxx/1.1 CFNetwork/548.1.4 Darwin/11.0.0
78.53.230.114 - - [11/Mar/2012:07:32:47 -0700] "POST /api/yyy HTTP/1.1" 200 94 - "zzz/1.1 CFNetwork/548.1.4 Darwin/11.0.0" "zzz.appspot.com" ms=16812 cpu_ms=6040 api_cpu_ms=82 cpm_usd=0.167820 pending_ms=5765 instance=00c71b117ca3858c47bdc41d5b30a732dd76eaaf
I 2012-03-11 15:32:37.196
www.server.xxxServlet getvvv: 1
I 2012-03-11 15:32:37.202
www.server.xxxServlet getvvv: hash
I 2012-03-11 15:32:37.207
www.server.xxxServlet getvvv: get PM (PersistenceManager pm = PMF.get().getPersistenceManager();)
I 2012-03-11 15:32:43.606
www.server.xxxServlet getvvv: get data
I 2012-03-11 15:32:47.355
www.server.xxxServlet getvvv: got data
I 2012-03-11 15:32:47.388
www.server.xxxServlet getvvv: done

      

        
        
        
      

    

and PMF is implemented as:

public final class PMF {
    private static final PersistenceManagerFactory pmfInstance =
        JDOHelper.getPersistenceManagerFactory("transactions-optional");

    private PMF() {}

    public static PersistenceManagerFactory get() {
        return pmfInstance;
    }
}