4. Size Cache Overview

To implement the Size Cache, you must:

1. implement the Cache interface
2. implement a class to carry out the logic of "size-based invalidation"

4.1. Implementing the Cache interface

The following code implements some methods in the Cache API.

PluginCache

Class Name	oracle.reports.plugin.cache.size.PluginCache
Description	This is the implementation of the Cache interface
implements	oracle.reports.cache.Cache

1. newItem(job, instanceKey)

This method creates a new item in cache system for the given job.

2. deleteItem(item)

This method deletes the cache item referred to by the parameter item.

3. findItem(jobProps)

This method gets the job properties and matches them with earlier job request. It returns the matching report output from cache. It returns null if a matching item is not found.

4.2. Implement the class for size-based invalidation

The following code handles the implementation ofthe SizeCache class. This class ensures that the limit sizeCache is respected by deleting files from cache directory. You can reuse this class to implement your custom logic for maintaining the Cache size within specified limits.

SizeCache

The default cache logic used in Oracle Reports is FIFO (first-in first-out). As an example, when the cache hits the maximum size limit, the oldest file in the cache directory is identified and deleted. This step is repeated until size of the cache reaches the specified limit, or until there are no more files in the cache (whichever condition occurs earlier). This logic is useful in situations where you do not need to keep cached copies of your old reports. For example, if you are using Oracle Reports to generate monthly reports of rented out books in your library, and you are not interested in keeping the cached copies of your old reports, you can use the default FIFO logic to manage the cache size.

On the other hand, the SizeCache class implements the "delete biggest 5 files" logic to maintain the Cache size limit. As an example, suppose the cache hits the maximum size limit when the 10th file is written to the cache directory. At this time, this class will identify the biggest 5 files in the cache, and delete them.

The SizeCache logic has less overhead than the default logic. Once the biggest 5 files are deleted, chances are that files will not need to be deleted for a while. However, this logic comes with a compromise - in this logic, it is possible that the cached copy of the latest report is deleted because it is a large report. Note that the "delete biggest 5 files" logic has been chosen only to show a sample implementation of Cache class. You have to implement the logic that suits your particular situation.

1. start(props, trace)

This method Starts the Oracle9i Reports caching service. You can use this method to set all static information that you can load from the Reports Server configuration file. (server.conf file in the $ORACLE_HOME/reports/config directory). This method receives the properties object as a parameter, which contains the list of values in the configuration file. The following information is loaded from the properties object:

• maximum size of the cache
• maximum number of files in the cache
• cache directory

If the cache directory does not exist, it creates the directory.

2. manage()

This method deletes top 5 items from the cache directory based on the "biggest file size" logic. The logic is implemented as:

First check if either of the parameters - cache size or the maximum number of files allowed in cache - has been exceeded. If yes, iterate through the files in the cache directory, identify the biggest 5 files and delete them. Repeat this step until the size of the cache reaches the specified limit, or until there are no more files in the cache (whichever condition occurs earlier).

It is the manage() method that you will need to override to implement your own cache-maintenance logic.

3. empty()

It invokes the method deleteItem repetitively to delete all items in the cache.