On Wed, Oct 22, 2008 at 5:28 PM, Ian MacLarty <[EMAIL PROTECTED]>wrote: ...
> However the article > http://code.google.com/appengine/articles/transaction_isolation.html > gives the impression that the transaction isolation level is read > committed. That would imply that another concurrent transaction > *could* update the counter value after the get, but before the put > (even inside a transaction). While an update to an entity group is in progress, the datastore bounces other attempts to update the group. (The client retries several times before giving up.) It does this during the entire transaction, so the entity group will not change between the beginning of the transaction and the end of the transaction. In the increment_counter example, this includes the get() as well as the put(). The client knows which group to update because it queues all datastore changes during the transaction code, then executes them all at the end. The transaction isolation article is more about reads. Reads succeed even while another client is performing an update. Up to the first milestone, reads return the entity in the state prior to the update. After the first milestone but before the second, reads return the entity in its new state, but queries match the old state. After the second milestone, both reads and queries use the new state. > Would someone mind clarifying this for me? Is the counter example > above guaranteed to atomically update the counter if it succeeds? If > that is the case, then I think the isolation level article is a bit > misleading, because the isolation level would be closer to > serializable. Are there a particular passages in the article that imply this? Maybe it could be clarified in the text. Thanks! -- Dan --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Google App Engine" group. To post to this group, send email to google-appengine@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en -~----------~----~----~----~------~----~------~--~---
