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Asked: 2026-05-26T11:05:51+00:00

I am a newbie to google app engine stuff. I am reading about app

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I am a newbie to google app engine stuff. I am reading about app engine from yesterday. I have a doubt regarding the write transaction during request time out.

Suppose that I am creating 10,000 objects and trying it to save through a single transaction (assuming that DatastoreService is like a Hibernate Transaction) like this

    String greeting = "test";
    String guestBookName = "default";
    DatastoreService datastoreService = DatastoreServiceFactory.getDatastoreService();
    Key guestBookKey = KeyFactory.createKey("GuestBook", guestBookName);
    for(int i=0;i<10000;i++)
    {
        Entity entity = new Entity("Greeting", guestBookKey);
        entity.setProperty("date", new Date());
        entity.setProperty("greeting", greeting);
        datastoreService.put(entity);
    }

Suppose that after saving 1000 objects, it the request timed out will 1000 objects be deleted?

I have run this code on app engine, after saving 1164 objects to the datastore the request timed out. I got this error

....Uncaught exception from servlet
com.google.apphosting.api.DeadlineExceededException: This request (0000000000000000)
started at 2011/10/20 07:18:36.726 UTC and was still executing at 2011/10/20 07:19:36.143 UTC.....

The objects were not removed from the datastore. Besides I read here that

The datastore can execute multiple operations in a single transaction. By definition, a transaction cannot succeed unless every operation in the transaction succeeds. If any of the operations fail, the transaction is automatically rolled back. This is especially useful for distributed web applications, where multiple users may be accessing or manipulating the same data at the same time.

Can anyone please help me understand about this clearly.

Thank you all in advance.

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1 Answer

  1. Editorial Team

    GAE transactions are working only against Entity Group (elements who have same root/parent). And second – it’s using optimistic locking, that means that transaction fails when other tread has made changes before current.

    It’s not traditional transactions. Your object will not be deleted if transaction your code fails

    Please read http://code.google.com/intl/en/appengine/docs/java/datastore/overview.html#Transactions_and_Entity_Groups

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