Oracle Coherence: In-place and Parallel Processing

In many situations, you can improve performance enormously if you perform the processing where the data is stored, instead of retrieving the data that needs to be processed. For example, while working with a relational database, you can use bulk update or a stored procedure to update many records without moving any data across the network.

Coherence allows you to achieve the same thing. Instead of retrieving the whole dataset that needs to be processed and iterating over it on a single machine, you can create an entry processor—a class that encapsulates the logic you want to execute for each object in a target dataset. You can then submit an instance of the processor into the cluster, and it will be executed locally on each node. By doing so, you eliminate the need to move a large amount of data across the network. The entry processor itself is typically very small and allows processing to occur in parallel.

The performance benefit of this approach is tremendous. Entry processors, just like distributed queries, execute in parallel across grid nodes. This allows you to improve performance by simply spreading your data across more nodes.

Coherence also provides a grid-enabled implementation of CommonJ Work Manager, which is the basis for JSR-237. This allows you to submit a collection of work items that Coherence will execute "in parallel" across the grid. Again, the more nodes you have in the grid, the more work items can be executed in parallel, thereby improving the overall performance.

Cache events

In many applications, it is useful to know when a particular piece of data changes. For example, you might need to update a stock price on the screen as it changes, or alert the user if a new workflow task is assigned to them.

The easiest and the most common solution is to periodically poll the server to see if the information on the client needs to be updated. This is essentially what Outlook does when it checks for new e-mail on the POP3 mail server, and you (the user) control how often the polling should happen.

The problem with polling is that the more frequently it occurs, the more load it puts on the server, decreasing its scalability, even if there is no new information to be retrieved.

On the other hand, if the server knows which information you are interested in, it can pus

h that information to you. This is how Outlook works with Exchange Server—when the new mail arrives, the Exchange Server notifies Outlook about this event, and Outlook displays the new message in your inbox. Coherence allows you to register interest in a specific cache, a specific item, or even a specific subset of the data within the cache using a query. You can specify if you are interested in cache insertions, updates or deletions only, as well as whether you would like to receive the old and the new cache value with the event.

As the events occur in the cluster, your application is notified and can take the appropriate action, without the need to poll the server.