Parallel Transactions in distinct Session in NHibernate / SQL Server

Question

we are building a WinForms desktop application which talks to an SQL Server through NHibernate. After extensive research we settled on the Session / Form strategy using Ninject to inject a new ISession into each Form (or the backing controller to be precise). So far it is working decently.

Unfortunately the main Form holds a lot of data (mostly read-only) which gets stale after some time. To prevent this we implemented a background service (really just a seperate class) which polls the DB for changes and issues an event which lets the main form selectively update the changed rows.

This background service also gets a separate session to minimize interference with the other forms. Our understanding was that it is possible to open a transaction per session in parallel as long as they are not nested.

Sadly this doesn't seem to be the case and we either get an ObjectDisposedException in one of the forms or the service (because the service session used an existing transaction from on of the forms and committed it, which fails the commit in the form or the other way round) or we get an InvalidOperationException stating that "Parallel transactions are not supported by SQL Server".

Is there really no way to open more than one transaction in parallel (across separate sessions)? And alternatively is there a better way to update stale data in a long running form?

Thanks in advance!

Answer 1

I'm pretty sure you have messed something up, and are sharing either session or connection instances in ways you did not intend.

It can depend a bit on which sort of transactions you use:

• If you use only NHibernate transactions (session.BeginTransaction()), each session acts independently. Unless you do something special to insert your own underlying database connections (and made an error there), each session will have their own connection and transaction.
• If you use TransactionScope from System.Transactions in addition to the NHibernate transactions, you need to be careful about thread handling and the TransactionScopeOption. Otherwise different parts of your code may unexpectedly share the same transaction if a single thread runs through both parts and you haven't used TransactionScopeOption.RequiresNew.

Perhaps you are not properly disposing your transactions (and sessions)?