jpa cache level 2 performance is bad

version appengine java sdk 1.6.4.1 
datanucleus jpa2.0.0 
datanucleus cache 3.0.1

hi all

i am using the DN cache level 2 plugin.

<property name="datanucleus.cache.level2.type" value="javax.cache"/>
<property name="datanucleus.cache.level2.cacheName" value="xxxxx"/>
i noticed a performance issue with a straight forward query.

Query query = em.createQuery("Select m.key from MessageUser m "
                + "where " + " m.userKeyList = :userKey "
                + "AND m.date > :date ORDER BY m.date DESC");
with the cache ON it execute in 1159 ms, cache OFF 86 ms.

something is clearly wrong. from the appstats trace the cache version is 
retrieving each entity in a serial manner from memcache.

cache OFF

(1) 2012-04-12 06:19:38.737 "GET 
/timeline/status?id=49001&sincedate=1333485300" 200  real=86ms api=0ms 
overhead=0ms (6 RPCs) 

@11ms datastore_v3.RunQuery real=10ms api=241ms
@31ms datastore_v3.Get real=7ms api=208ms
@4ms datastore_v3.BeginTransaction real=4ms api=0ms
@52ms datastore_v3.Get real=7ms api=8ms
@65ms datastore_v3.Get real=4ms api=0ms
@78ms datastore_v3.Commit real=4ms api=0ms 
cache ON

9) 2012-04-12 05:54:24.385 "GET /timeline/status?id=49001&sincedate=1333485300" 
200 real=1159ms api=0ms overhead=0ms (109 RPCs) 
@13ms datastore_v3.RunQuery real=12ms api=241ms
@28ms memcache.Get real=2ms api=0ms
@33ms memcache.Get real=2ms api=0ms
@37ms memcache.Get real=3ms api=0ms
@42ms memcache.Get real=2ms api=0ms
@47ms memcache.Get real=2ms api=0ms
@50ms memcache.Get real=2ms api=0ms
@54ms memcache.Get real=2ms api=0ms
@57ms memcache.Get real=2ms api=0ms
<repeat this for another 50 or60 times
@3ms datastore_v3.BeginTransaction real=4ms api=0ms
@1126ms datastore_v3.Get real=5ms api=8ms
@1134ms memcache.Get real=3ms api=0ms
@1139ms memcache.Get real=2ms api=0ms
@1143ms datastore_v3.Get real=4ms api=0ms
@1153ms datastore_v3.Commit real=3ms api=0ms 

the code that iterates the entity list

List<Message> list = messageDAO.findSinceDate(userKey, sinceDate);

JSONArray jsonList = new JSONArray();

for (Message message : list) {
item.put("id", message.getKey().getId());
    item.put("name", message.getName());
}

the performance using the DN level 2 cache is an order of magnitude worse than 
not using cache.
Original issue reported on code.google.com by lu...@asteriski.com on 15 Apr 2012 at 2:30
jplams / datanucleus-appengine

jpa cache level 2 performance is bad #278
