Skip to main content

OpenSessionInView Filter, Sessions, Transactions and Connections

By now, I have worked enough on OpenSessionInViewFilter, Hibernate and Spring in some projects.

Hibernate 3 uses Lazy Loading by default. So, We use for maintaining lazy loaded collections to display in view. But, lately, as I mentioned in earlier posts, we were having some issues with connections that were not returned to pool.

To understand where connections were held up we need to see how OSIVfilter, Session, HibernateTransactionManager and Spring work together - Where and when connections are picked and released. OSIVFilter guarentees that each request will have one and only one Hibernate Session. A Session is a lightweight abstraction of data in the database pulled into vm converted as objects. So for a session to fetch data from db, it needs connections. This connection is available from the datasource through a TransactionManager. In general, if you have one database, You would use Springs HibernateTransactionManager.

A Session generally contains one Transaction. However, In OSIV pattern, You keep the session for conversation. This means, You could have multiple transactions in a request. So What happens is, Session syncs with database on multiple transactions. However, Session *doesnot* need to hold the *same* connection throughout the request (it may happen that the pool returned the same connection int he second call, but it is not necessary)

But the TransactionManger will need the same connection all through the transaction. So IT is the one that borrows connection from the pool. When does it release the connection? Pre Hib 3, Session and Transaction was defacto considered the same - So the connections were released only at the end of the session. For Hib 3.1 and later, ConnectionReleaseMode was introduced, which defaults to on_transaction which releases after each transaction. So this way you could use OSIV pattern, scalably. You *can* (by all logical means should not) change it to on_session.

Popular posts from this blog

One page Stock

Alright.. That was a long absence. The whole last week I dint blog. I dint go away. I was "occupied". I was learning stock trading. Its very fascinating. I have a good weeeked blog for you all. Here is my experience. I can literally hyper-link every word from the following paragraphs, but I am writing it as simple as I can so you can look up the italicised words in wikipedia . I got a paper trading account from a brokerage firm . You need one brokerage account first. Then it can be an Equity account where all your money is yours or a Margin account , where some of the money is lent by the brokerage firm. Then I get Buying power , which is the dollor value of how much stocks you can buy. I can make profit by simple rules. Buy when Price is low. Sell when price is high. There is another more intersting way of earning money. Selling short . Thats when price is not high, per say, but when are confident that the price WILL go down. then buy back when its lowest. This is what

Powered By

As it goes, We ought to give thanks to people who power us. This page will be updated, like the version page , to show all the tools, and people this site is Powered By! Ubuntu GIMP Firebug Blogger Google [AppEngine, Ajax and other Apis] AddtoAny Project Fondue jQuery

classpath*: making your Modular Spring Resources

Spring gives multiple options to load XML resources for building contexts. the reference documentation does explain this feature quite well. However, I am taking my shot at explaining the different practical scenarios ( by order of growing modularisation) For Example, A simplest Spring based web Context Loader can be configured with resources like this <context-param> <param-name>contextConfigLocation</param-name> <param-value>applicationContext.xml</param-value> </context-param> <listener> <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class> </listener> You just need to put applicationContext.xml in WEB-INF/ folder of your webapp. However, Typically an application is n-tiered. You can also have multiple files setup and in relative paths. like <param-value> context-files/applicationContext.xml context-files/dao.xml context-files/service.xml </param-value>