successful in understanding google app engine .finished learning a full project,awesome concepts

the whole project can be downloaded form http://www.mediafire.com/?2cwxmg5i2cnl3f6
Understanding datastore??
references:-https://developers.google.com/appengine/docs/java/gettingstarted/usingdatastore

 DatastoreService datastore =  DatastoreServiceFactory.getDatastoreService();     datastore.put(greeting);

Because querying in the High Replication datastore is only strongly consistent within entity groups, we assign all Greetings to the same entity group by setting the same parent for each Greeting. This means a user will always see a Greeting immediately after it was written. However, the rate at which you can write to the same entity group is limited to 1 write to the entity group per second.
The low-level Java API provides a Query class for constructing queries and a PreparedQuery class for fetching and returning the entities that match the query from the datastore. The code that fetches the data is here:

Query query = new Query("Greeting", guestbookKey).addSort("date",Query.SortDirection.DESCENDING);
   List<Entity> greetings = datastore.prepare(query).asList(FetchOptions.Builder.withLimit(10));

follow this link:

https://appengine.google.com/->newapps6974(my app name)->datastore indexes
in the datastore indexes you will see the entity name and indexes.refer to the datastore-indexes,xml file now and see the matching.

see the datastore viewer.you will see the mesages in the descending order(datewise)).awesome.