Understanding Transactions

Question

Reading the forum I read this post:
You need to configure transactions in your EnvironmentConfig and when you create/open your containers. E.g.:
envConf.setTransactional(true);
container = manager.openContainer(cname, new XmlContainerConfig.setTransactional(true));
Then you need to use explicit transactions in your application and be prepared to receive and handle deadlock exceptions (handle them via retrying the operation, after aborting the transaction).
So my question is what are the rules. By this I mean when I open my container I am using the flag DBXML_TRANSACTIONAL. However in some cases when i perform just a query I do not explicitly create a transaction, is that bad? I guess the question is what methods must I use explicit transactions?
Next when I do explicitly create a transaction if I do it in this order:
txn = DBManager->Manager->createTransaction();
container = DBManager->Manager->openContainer(path, flags);
container.putDocument(txn, doc, ctx);
Is this bad?, Some of the examples imply the order should be open the container, create the transaction, then put the document.
Thanks
Jim

Answer 1

Jim,
A few general rules:
1. open/create containers separately from operations on them. Usually an application will open a container when it starts up and close/delete it when it shuts down. Unless you are running in a CGI script where it's unavoidable that is what you should do too.
2. use the DBXML_TRANSACTIONAL flag or XmlContainerConfig.setTransactional(true) when opening containers. If you do this you do not need an explicit transaction for the open/create operation.
3. when using any container- or XmlManager-based operation for which there is a variant that takes an XmlTransaction parameter you should specify one and be prepared to handle a deadlock exception and abort and retry the operation. This applies to read (e.g. query) as well as update (e.g. putDocument) operations.
A few more rules:
4. always start your transactional application single-threaded and be sure to run recovery on your Environment before any other thread or process can access it.
5. always attempt to shut down cleanly -- closing (deleting) containers, managers, and environment (in that order). Again, this should be single-threaded with no other threads inside of the BDB XML or DB API.
Regards,
George