Welcome!

Weblogic Authors: Yeshim Deniz, Elizabeth White, Michael Meiner, Michael Bushong, Avi Rosenthal

Related Topics: Weblogic

Weblogic: Article

Implementing a Cluster-Aware Cache Using WebLogic

A lazily reconstructable cache system that notifies cluster members of deletes

Caching information on the WebLogic tier can significantly increase performance and reduce the number of external system calls needed for data retrieval. This is especially true when an application wants to store bits of information that rarely change, such as a list of countries or catalog entries. Nowadays, memory is so cheap that application architectures can benefit from caching data on the Web/EJB tiers.

This is not a new concept; most developers already do this. Whether it's accessing data from a simple java.util.Hashtable or java.util.Hashmap, or using a sophisticated LRU cache mechanism (a derivative of LinkedList), there is minimal overhead in accessing information. The real question isn't how the data is cached or what mechanism is used for storage, but how to preserve the data's integrity and notify cluster members of changes in a highly available, clustered environment.

For example, suppose you're building an e-commerce storefront application that sells clothing. The product information such as the item name, description, SKU, price, and image can be stored in memory on the application tier. The benefit of storing the data in memory is faster page loading and a reduction in database calls.

Now, what happens when your business user wants to change the price or description of the catalog item? How would you notify all of the members of the cluster of this "delta" change? Remember, you probably still want the data to be stored in memory if possible for performance reasons. Also, you probably want the information to be updated in close real-time and don't want to reload all of the data if it hasn't changed.

This article illustrates a simple technique for implementing a "lazily reconstructable" cache system that notifies cluster members of invalidations (deletes).

For example, look at the following code:


static Hashtable cache = new Hashtable();

public Product getProduct(String productID) {
Product product = (Product) cache.get(productID);
if (product == null) {
// get the product from the database
product = ProductDAO.getProduct(productID);
cache.put(productID, product);
}
return product;
}
A simple java.util.Hashtable stores the list of products indexed by the product identifier in a static cache. Products are retrieved from the database and added to the cache lazily if they don't already exist. This code snippet demonstrates how to retrieve a product by looking into cache and grabbing it if it doesn't exist.

What happens if a product description changes for a specific product? Look at this code:


public void changeDescription(String productID, String newDescription)
throws ProductNotFoundException {

ProductDAO.changeDescription(productID, newDescription);

Command command = new InvalidateCacheCommand(productID);
ClusterNotifier.notify(command);
}
The code behind the ProductDAO.changeDescription method updates the product ID in the database with the new description. The ClusterNotifier.notify method (see Listing 2) will delete the product from the local cache and send an invalidation event to the cluster members to delete the product from its local cache. Once this is done, all of the members in the cluster will have the product removed from memory. If a user requests this product on any node, it becomes lazily initialized with the new description that was set. See the snippet below from getProduct() example:

if (product == null) {
// get the product from the database
product = ProductDAO.getProduct(productID);
cache.put(productID, product);
}
This will reinitialize the product from the database and insert the information back into cache.

How does this work? Well, let's take a look.

Deep Dive into the Classes
Note: This article uses unpublished private APIs from WebLogic. They work with WebLogic 7.x and 8.x, but there's no guarantee they'll be supported in future versions. Many of the underlying details were "introspected" by putting the WebLogic.jar in the classpath of the IDE.

Command Interface (Generic)
First, let's take a look at the Command interface. It's simple. It defines a single method called "execute."


public interface Command extends Serializable {
public void execute();
}
The Command interface is used to do the work that needs to be done in the cluster. Notice that it is Serializable. It contains the logic to do a task when it reaches each cluster member. This interface is generic enough to do any operation. This article discusses how this interface can be used to invalidate keys in a cache across the cluster.

InvalidateCacheCommand Concrete Implementation (Specific)
The class in Listing 1 is a concrete implementation of the Command interface to invalidate the keys in a cache. Notice that the execute method clears the entry of a statically bound cache. How does this work?

More Stories By Bahar Limaye

Bahar Limaye is a system architect at The College Board. He has extensive experience building distributed object-oriented systems.

Comments (1)

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


IoT & Smart Cities Stories
Nicolas Fierro is CEO of MIMIR Blockchain Solutions. He is a programmer, technologist, and operations dev who has worked with Ethereum and blockchain since 2014. His knowledge in blockchain dates to when he performed dev ops services to the Ethereum Foundation as one the privileged few developers to work with the original core team in Switzerland.
In his general session at 19th Cloud Expo, Manish Dixit, VP of Product and Engineering at Dice, discussed how Dice leverages data insights and tools to help both tech professionals and recruiters better understand how skills relate to each other and which skills are in high demand using interactive visualizations and salary indicator tools to maximize earning potential. Manish Dixit is VP of Product and Engineering at Dice. As the leader of the Product, Engineering and Data Sciences team at D...
Dynatrace is an application performance management software company with products for the information technology departments and digital business owners of medium and large businesses. Building the Future of Monitoring with Artificial Intelligence. Today we can collect lots and lots of performance data. We build beautiful dashboards and even have fancy query languages to access and transform the data. Still performance data is a secret language only a couple of people understand. The more busine...
Bill Schmarzo, author of "Big Data: Understanding How Data Powers Big Business" and "Big Data MBA: Driving Business Strategies with Data Science," is responsible for setting the strategy and defining the Big Data service offerings and capabilities for EMC Global Services Big Data Practice. As the CTO for the Big Data Practice, he is responsible for working with organizations to help them identify where and how to start their big data journeys. He's written several white papers, is an avid blogge...
René Bostic is the Technical VP of the IBM Cloud Unit in North America. Enjoying her career with IBM during the modern millennial technological era, she is an expert in cloud computing, DevOps and emerging cloud technologies such as Blockchain. Her strengths and core competencies include a proven record of accomplishments in consensus building at all levels to assess, plan, and implement enterprise and cloud computing solutions. René is a member of the Society of Women Engineers (SWE) and a m...
Andrew Keys is Co-Founder of ConsenSys Enterprise. He comes to ConsenSys Enterprise with capital markets, technology and entrepreneurial experience. Previously, he worked for UBS investment bank in equities analysis. Later, he was responsible for the creation and distribution of life settlement products to hedge funds and investment banks. After, he co-founded a revenue cycle management company where he learned about Bitcoin and eventually Ethereal. Andrew's role at ConsenSys Enterprise is a mul...
Whenever a new technology hits the high points of hype, everyone starts talking about it like it will solve all their business problems. Blockchain is one of those technologies. According to Gartner's latest report on the hype cycle of emerging technologies, blockchain has just passed the peak of their hype cycle curve. If you read the news articles about it, one would think it has taken over the technology world. No disruptive technology is without its challenges and potential impediments t...
If a machine can invent, does this mean the end of the patent system as we know it? The patent system, both in the US and Europe, allows companies to protect their inventions and helps foster innovation. However, Artificial Intelligence (AI) could be set to disrupt the patent system as we know it. This talk will examine how AI may change the patent landscape in the years to come. Furthermore, ways in which companies can best protect their AI related inventions will be examined from both a US and...
Bill Schmarzo, Tech Chair of "Big Data | Analytics" of upcoming CloudEXPO | DXWorldEXPO New York (November 12-13, 2018, New York City) today announced the outline and schedule of the track. "The track has been designed in experience/degree order," said Schmarzo. "So, that folks who attend the entire track can leave the conference with some of the skills necessary to get their work done when they get back to their offices. It actually ties back to some work that I'm doing at the University of San...
When talking IoT we often focus on the devices, the sensors, the hardware itself. The new smart appliances, the new smart or self-driving cars (which are amalgamations of many ‘things'). When we are looking at the world of IoT, we should take a step back, look at the big picture. What value are these devices providing. IoT is not about the devices, its about the data consumed and generated. The devices are tools, mechanisms, conduits. This paper discusses the considerations when dealing with the...