objectify cache not working

Question

I am using GAE for my server where I have all my entities in Datastore. One of the entity has more than 2000 records, and it is taking almost 30 secs to read whole entity. So I wanted to use cache to improve performance.

1. I have tried Datastore objectify @cache annotation, but not finding how to read from the stored cache. I have declared entity as below:

   @Entity
   @Cache
   public class Devices{
   }
   

2. Second thing I tried is memcache. I am storing whole List s in key, but this is not storing, I couldn't see in console memcache, but at the same time not showing any errors or exceptions while storing objects.

   putvalue("temp", List<Devices>)
   
   public void putValue(String key, Object value) {
       Cache cache = getCache();
       logger.info(TAG + "getCache() :: storing memcache for key : " + key);
       try {
         if (cache != null) {
           cache.put(key, value);
         }
       }catch (Exception e) {
         logger.info(TAG + "getCache() :: exception : " + e);
       }
   }
   

   When I tried to retrieve using getValue("temp"), it is returning null or empty.

   Object object =  cache.get(key);
   

My main object is to limit the time to 5secs to get all the records of entity. Can anyone suggest what I am doing wrong here? Or any better solution to retrieve the records fast from Datastore.

Answer 1

1. Datastore Objectify actually uses the App Engine Memcache service to cache your entity data globally when you use the @Cache annotation. However, as explained in the doc here, only get-by-key, save(), and delete() interact with the cache. Query operations are not cached.
2. Regarding the App Engine Memcache method, you may be hitting the limit for the maximum size of a cached data value which is 1 MiB, although I believe this raise an exception indeed.

Regarding the query itself, you may be better off using a keys_only query and then doing a key.get() on each returned key. That way, Memcache will be used for each record.