I have a fairly simple App Engine Java app that has Accounts, Orders and
OrderItems - nothing crazy.
Just in the last 12 hours I have started getting exceptions thrown out of
some fairly straight forward code that adds orders to accounts and then
saves them.
I created a trivial testing servlet to replicate the issue, it looks like
this:
public void doGet(HttpServletRequest req, HttpServletResponse resp)
throws IOException {
String key = req.getParameter("key");
PersistenceManager pm = PMF.get().getPersistenceManager();
Account account = pm.getObjectById(Account.class,
KeyFactory.stringToKey(key));
Order order = new Order();
order.setExternalOrderID("ASHLEY-TESTING");
Item item = new Item();
item.setSku("ASHLEY-WIDGET-A");
item.setQuantity(2);
Item item2 = new Item();
item2.setSku("ASHLEY-WIDGET-B");
item2.setQuantity(2);
order.addItem(item);
order.addItem(item2);
account.addOrder(order);
order.setAccount(account);
pm.makePersistent(order);
pm.close();
}
addOrder is implemented as a pretty standard lazy init:
public void addOrder(Order order) {
if (getOrders() == null) {
setOrders(new ArrayList<Order>());
}
getOrders().add(order);
}
The relevant parts of the entities:
@PersistenceCapable
public class Account {
//...
@Persistent(mappedBy="account")
@javax.jdo.annotations.Order(extensions =
@Extension(vendorName="datanucleus", key="list-ordering", value="startDate
desc"))
private List<Stats> stats;
//...
}
and the Order has an account field:
@Persistent
private Account account;
This code is failing on the `account.addOrder()` line. If it is run directly
in the browser it fails with DeadlineExceededException (after 30s) and if I
enqueue it to run via a task queue it fails with DatastoreTimeoutException
after a minute or two. It uses a truck load of CPU time in the process.
I would estimate that the Account would have fewer than 2000 Orders children
under it, each Order with 1-3 OrderItem children.
My question is, why would this all of a sudden start failing it has worked
to add the 1000's of orders already in there. And have I missed something
vital? do I need to add indexes? could the data store really be this slow?
Am I abusing it, should I not have children relationships with this many
children - perhaps a set of keys would be a better approach?
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