2009 February | Solution Hacker

Archive | February, 2009

Hibernate vs iBatis

by admin on February 26, 2009 in Design, Site Building

Hibernate is great. However, I don’t see it fits all the data access requirements. At its core, it is an ORM tool that helps you to map your object model to relational model. If you have full control of your relational model and perform lots of CRUD operations, it is certainly a great tool for you. Its transparent persistence, 2 level caching, dirty checking, lazy/ eager data retrieval and sql generation indeed can save us lots of development time. However, one tool doesn’t fit all !! Why not?

In my current company, I have created a reporting tool that interfaces with dimensional model in data warehouse. In this setting, you will deal with star schema with denormalized dimensions. Often time, I need to tune the query performance via looking into explain plan. Without full control of SQL, my job will be hard to achieve. Apart from that, reporting tool often issues read-only set based queries to the data warehouse. The resultset returned doesn’t fit into my OO model at all. Again, Hibernate just doesn’t fit in. People in my company argue that I should use named query in Hibernate for the sake of sticking with the standard. I am like ok, whatever… I have known a tool called iBatis that I can achieve my job cleanly. Why the hell I would have motivation to try named query that basically a way to by-pass the ORM model to query database. What benefit I will get from this? The cache? We are using ETL to update our fact and dimension in the data warehouse, not by my reporting app. Unless the ETL throws me an event when the update cycle is finished so I can flush my cache, I simply don’t think it gives me lots of help.

Anyway, it is just my own little perspective. You don’t have to agree with me. The point here is not that I don’t like Hibernate but I don’t like to be pushed to use it only because it is “standard” to someone. If Hibernate could help me to construct my sql based on user input, stream my result directly to my presentation layer, populate my model automatically based on mapping I provided, detect data warehouse changes and take care my cache, then I am more happy to adopt it in my reporting app. Otherwise, I would not be eager to dump my iBatis DAO layer unless I get no choice under the political game.

Reference

Leave a comment • Continue Reading →

Concurrent Programming

by admin on February 17, 2009 in 6. Uncategorized

Blocking Queue

Behavior

Quite often in threaded applications we have a producer-consumer situation where some threads want to add jobs onto a queue, and some other worker threads want to remove jobs from the queue and then execute them. It is quite useful in such circumstances to write a queue which blocks on pop when there is nothing on the queue. Otherwise the consumers would have to poll, and polling is not very good because it wastes CPU cycles. When clients attempt to retrieve elements but none are available, a BlockingQueue encapsulates code that waits until an element becomes available.

Usage

The server runs infinitely, accepting requests from a client. Clients can send requests asynchronously and rapidly—the server only adds a client request to the server’s queue (ie. blocking queue), then returns immediately to the client. A separate server thread loops indefinitely, asking the BlockingQueue to return when a new request becomes available. Once a request is available, it’s removed from the queue. The server then handles the request.

Reference

Java Specialist – Blocking Queue

ReentrantLock

Behavior

ReentrantLock supports all of the lock-acquisition modes defined by Lock, providing more flexibility for dealing with lock unavailability than does synchronized. Intrinsic locking (ie. synchronized) works fine in most situations but has some functional limitations: It is not possible to interrupt a thread waiting to acquire a lock. If you want the lock, you need to prepare to wait for it forever. Using ReentrantLock, you have more flexibility and scalability:

Timed and Polled lock acquisition – Use tryLock(). One form of this method returns immediately if the lock is already held and the other can wait for some period of time for the lock to become available before giving up. In both cases, we could effectively loop and retry the tryLock() until it succeeds.
Interruptable lock acquisition – Use lockInterruptabily() allows locking to be used within cancellable activities
Non-block structured locking