Tune dynamic cache with the cache monitor

Operating Systems: i5/OS
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Tune dynamic cache with the cache monitor

Use this task to interpret cache monitor statistics to improve the performance of the dynamic cache service. Verify that dynamic cache is enabled and that the cache monitor application is installed on your application server.

Overview

See Displaying cache information to configure the cache monitor application. Use the cache monitor to watch cache hits versus misses. By comparing these two values, you can determine how much dynamic cache is helping your application, and if you can take any additional steps to further improve performance and decrease the cost of processing for your application server.

Procedure

Start cache monitor and click on Cache Statistics. You can view the following cache statistics:

Cache statistic Description
Cache Size The maximum number of entries that the cache can hold.
Used Entries The number of cache entries used.
Cache Hits The number of request responses that are served from the cache.
Cache Misses The number of request responses that are cacheable but cannot be served from the cache.
LRU Evictions The number of cache entries removed to make room for new cache entries.
Explicit Removals The number of cache entries removed or invalidated from the cache based on cache policies or were deleted from the cache through the cache monitor.

Cache statistic	Description
Cache Size	The maximum number of entries that the cache can hold.
Used Entries	The number of cache entries used.
Cache Hits	The number of request responses that are served from the cache.
Cache Misses	The number of request responses that are cacheable but cannot be served from the cache.
LRU Evictions	The number of cache entries removed to make room for new cache entries.
Explicit Removals	The number of cache entries removed or invalidated from the cache based on cache policies or were deleted from the cache through the cache monitor.

You can also view the following cache configuration values:

Cache configuration value Description
Default priority Specifies the default priority for all cache entries. Lower priority entries are moved from the cache before higher priority entries when the cache is full. You can specify the priority for individual cache entries in the cache policy.
Servlet Caching Enabled If servlet caching is enabled, results from servlets and JavaServer Pages files are cached. See Configuring servlet caching for more information.
Disk Offload Enabled Specifies if entries that are being removed from the cache are saved to disk. See Configuring dynamic cache disk offload for more information.

Wait for the application server to add data to the cache. You want the number of used cache entries in the cache monitor to be as high as it can go. When the number of used entries is at its highest, the cache can serve responses to as many requests as possible.
When the cache has a high number of used entries, reset the statistics. Watch the number of cache hits versus cache misses. If the number of hits is far greater than the number of misses, your cache configuration is optimal. You do not need to take any further actions. If you find a higher number of misses with a lower number of hits, the application server is working hard to generate responses instead of serving the request using a cached value. The application server might be making database queries, or running logic to respond to the requests.
If you have a large number of cache misses, increase the number of cache hits by improving the probability that a request can be served from the cache.
To improve the number of cache hits, you can increase the cache size or configure additional cache policies. See Dynamic cache service settings to increase the cache size and Configuring cacheable objects with the cachespec.xml file for information about configuring cache policies.

Cache configuration value	Description
Default priority	Specifies the default priority for all cache entries. Lower priority entries are moved from the cache before higher priority entries when the cache is full. You can specify the priority for individual cache entries in the cache policy.
Servlet Caching Enabled	If servlet caching is enabled, results from servlets and JavaServer Pages files are cached. See Configuring servlet caching for more information.
Disk Offload Enabled	Specifies if entries that are being removed from the cache are saved to disk. See Configuring dynamic cache disk offload for more information.

Results

By using the cache monitor application, you optimized the performance of the dynamic cache service.

What to do next

See Task overview: Using the dynamic cache service to improve performance for more information about the dynamic cache.

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Related concepts

Cache monitor