Home/ Questions/Q 7572005
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-30T15:48:51+00:00

I have a question about the examples in this article: http://code.google.com/appengine/articles/transaction_isolation.html Suppose I put

  • 0

I have a question about the examples in this article:

http://code.google.com/appengine/articles/transaction_isolation.html

Suppose I put Adam and Bob in the same entity group and modify the operation getTallPeople to only check the height of Adam and Bob (i.e. access only entities in the entity group). Now, if I execute the following statements:

begin transaction
updatePerson (update Adam's height to 74 inches)
commit transaction

begin transaction
getTallPeople
commit transaction

Can I be sure that getTallPeople will always return both Adam and Bob? I.e. if entity/index updates have not completed, will the second transaction wait until they have? Also, would the behavior be the same without using a transaction for getTallPeople?

Thanks for your help!

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    Yes. For getTallPeople to be called within a transaction, it must use an “ancestor” filter in its query to limit its results to members of the group. If it does so, both the index data it uses to determine the results and the entities it fetches based on those results will be strongly consistent with the committed results of the previous transaction. This is also true without the explicit transaction if the query uses an ancestor filter and you’re using the HR datastore. (The HR datastore has been the default for a while, so you’re probably using it.)

    If getTallPeople performs a query without an ancestor filter and you’re using the HR datastore, it will use the global index data, which is only guaranteed to be eventually consistent across the dataset. In this case, the query might see index data for the group prior to the previous transaction, even though the previous transaction has already committed.

    • 0