在长时间运行过程中使用NHibernate更新状态表

Question

I have inherited a project that implements multiple long running processes. Each of those processes update a status table that is then reflected on the UI via ajax polling. These process are running in a background application that uses Rhino Service Bus (with MSMQ), and the process is triggered by sending an "execute long process" message.

The process itself is doing all kinds of data manipulation, validation, updates, inserts deletes etc. on numerous tables.

It seems like it is really abusing the NHibernate session with multiple sessions and nested TransactionScopes all over the place.

My question to the NHibernate / RSB experts out there, is how would you update a status table during the execution of a long running process?

I have thought about:

• sending an "update status message" during the execution of the process (will need to workout the NHibernate / RSB session management issues).
• using a saga with database persister and have the ajax polling functions query it instead of a status table

Answer 1

The problem with status updates within a RSB process is that typically, the message processing happens inside a transaction scope itself. This means that any changes to the database, or messages you send, will only (typically) be visible to other applications once the transaction is committed (which happens when processing the message is complete).

There are 3 approaches I typically take:

1. wrap the updates in a TransactionScope that suppresses the ambient transaction (I suspect that this is what is currently happening)
2. break the process down into smaller messages (this could reduce contention on the database, but at the cost of having more messages flying around)
3. notify external clients by means of some other process (eg. have some kind of remoting service / WCF / rest service that other processes can query, or send out notifications via some kind of transaction ignorant process)