This function is really cool. Many thanks for saving my money and
time.
With GAE and Objectify's help, I will hopefully release my Android/GAE
MMO game on Apr,1
On Mar 26, 5:14 am, Duong BaTien wrote:
> Hi:
>
> Congratulation and thank for tremendous efforts from the Objectify Team.
>
> By the way, has any one attempted Objectify with possible very large
> index of subscribers and publishers of web-hook pub-sub (Google
> PubSubHubbub of Atom or short message twitter style).
>
> Thanks
> Duong BaTien
> DBGROUPS and BudhNet
>
> On Thu, 2010-03-25 at 13:45 -0700, Jeff Schnitzer wrote:
> > Today we released Objectify v2.1, the latest version of our opensource
> > replacement for JDO/JPA on the Google App Engine datastore.
>
> > This version includes a major new feature, Partial Indexes. If you
> > aren't sure what partial indexes are, the Wikipedia page
> > (http://en.wikipedia.org/wiki/Partial_index) describes them so:
>
> > "A partial index, also known as filtered index is a database index
> > which has some condition applied to it such that it only includes a
> > portion of the rows in the table. This can allow the index to remain
> > small even though the table may be rather large, and have fairly
> > extreme selectivity."
>
> > Here is an example of an Objectify entity using partial indexes:
>
> > public class Player {
> > @Id Long id;
>
> > // Simple conditions: IfFalse, IfTrue, IfZero, IfNull, etc
> > @Unindexed(IfFalse.class) boolean admin;
>
> > // Smarter - sensitive to the actual default value
> > @Unindexed(IfDefault.class) Team team = Team.NOTCHOSEN;
>
> > // You can make your own conditions
> > @Unindexed(IfCustomCondition.class) Status status;
>
> > static class IfCustomCondition extends ValueIf {
> > public boolean matches(Status value) {
> > return (value == Status.DEAD || value == Status.RETIRED);
> > }
> > }
> > }
>
> > Why should you care about optimizing indexes?
>
> > All queries in the datastore require indexes, which are a sort of
> > reverse-mapping from value to key. These indexes occupy space and
> > consume cpu resources whenever an entity is written to the datastore.
> > With the addition of just a few indexes, this cost quickly doubles or
> > triples the cost of storing the original entity:
>
> > * A basic entity with no indexes costs 48 api_cpu_ms to store.
> > * Each single-property indexed field adds an additional 17 api_cpu_ms.
>
> > This number appears stable and consistent; appengine seems to have a
> > static formula for computing datastore costs. Storage size costs are
> > harder to measure, but from watching mailing list traffic it seems
> > quite easy to double or triple your storage size with unnecessary
> > indexes.
>
> > When should you care about optimizing indexes?
>
> > * Removing unnecessary indexes will not make writes faster, it will
> > make them /cheaper/. All indexes are written in parallel, so indexes
> > do not add latency to writes. Instead, indexes add $ to the bill you
> > get at the end of the week - and push you closer to your quota limits.
>
> > * If your application has relatively small quantities of relatively
> > static data, index optimization is probably pointless. On the other
> > hand, if you have large data volumes or heavy write loads, you must
> > carefully choose your indexes (or be very rich).
>
> > Do I need partial indexes, as opposed to just declaring whole fields
> > indexed or not?
>
> > It depends on your dataset and your queries. In the Player example
> > above, partial indexes can be extremely effective:
>
> > * You only ever filter on the admin field for actual admins, and most
> > players are not admins.
> > * You only ever filter on the team field for players who have chosen
> > a team, and the bulk of players are not associated with a team.
> > * You only ever filter on the status field for players who have
> > active statuses, and you have a large number of inactive players.
>
> > Objectify's support for partial indexes also has the ability to
> > determine index behavior based on "the whole entity". This allows you
> > to perform certain kinds of limited multiple-property queries
> > (including double inequality queries) without creating a
> > multi-property index. As an example, it is very easy to model this
> > index from the Wikipedia page:
>
> > create index partial_salary on employee(age) where salary > 2100;
>
> > An example of this is documented in the Objectify manual.
>
> > Thanks,
> > The Objectify Team
> > Jeff, Scott, and Matt
>
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