I don't use JPA, but the way I understand it is that a get is by key which
can also be a batch get by key. Whereas a query, queries for the entity keys
using an index and then gets the entities by key. So, the way I understand
it is below, but this is just my understanding so I could be wrong:
HR DATASTORE
-------------------------------------------------------------------------------------------------------------------------
| |
CONSISTENCY SETTING |
| ACTION | STRONG |
EVENTUAL |
|-----------------------------------------------------------------------------------------------------------------------|
| GET BY KEY | STRONG |
EVENTUAL |
| ANCESTOR QUERY | STRONG |
EVENTUAL |
| NON-ANCESTOR QUERY | EVENTUAL/STRONG | EVENTUAL |
------------------------------------------------------------------------------------------------------------------------
* For non-ancestor query with strong consistency, the indexes are eventually
consistent but the entities should be strongly consistent (I think???).
Stephen
On Sun, Jul 10, 2011 at 5:36 PM, bejayoharen <[email protected]> wrote:
> Thank you, this is helpful, especially the links.
>
> I am using JPA and it's not clear to me what constitutes a "get" --
> does calling EntityManager.find() always constitute a "get" or only
> when the @Id of my class is the same as the underlying datastore key?
>
> Furthermore, the docs cited by Kyle indicate that a transaction will
> always return the most recently written data. However, that
> contradicts this
>
> http://code.google.com/appengine/docs/java/datastore/queries.html
>
> which says, "With the High Replication Datastore, non-ancestor queries
> are always eventually consistent."
>
> Which is it, are non-ancestor queries are always eventually
> consistent, or can transactions cause them to be strongly consistent?
>
> bjorn
>
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