More Transaction Questions

Question

I posted this under an answered question but realized I should have started a new thread.
Some more questions on transactions:
XmlTransaction txn = DBManager->Manager->createTransaction();
res = DBManager->Manager->query(txn, query.str(), queryContext, 0);
XmlValue on;
while( res.next(on) )
c->Response += on.asString();
txn.commit();
In the above code does the txn.commit() have to happen after the processing of the result? In other words what happens if the transaction is committed before the while loop?
Second question, in another section of the code I am doing similar to the above the difference is the query result is a list of documents to be deleted so the while loop is more like this:
while( res.next(on) )
container->deleteDocument(txn, on.asString(), context);
If I am deleting several thousand documents (in this case 2300) will there be an issue with the transaction being able to hold that many deletes?

Answer 1

Hello,
2 good questions.
1. It depends. If you have returned constructed content (e.g. return <foo>{...}</foo>) where the values will not refer to the container nodes then you can safely commit right after the query unless you are using lazy evaluation, in which case you cannot commit until you are done iterating. If any results may point into the container you cannot commit until you've processed them all or can otherwise guarantee that you won't touch the container outside the transactions.
If you violate the rule you'll get an exception saying so.
2. 2300 results isn't that large. The issues related to deleting so much content in a single transaction include:
a. a lot of data written to the log at commit time
b. using a fair bit of resource in terms of locks, etc
c. concurrency -- holding off other operations. document deletion is at least as time-consuming as insertion
If any of these are real problems for you, you could copy the document names somewhere and delete them in bite-size chunks in separate transactions.
Regards,
George