Dynamic cache service settings

Use this page to configure and manage the dynamic cache service settings.

To view this administrative console page, click Servers > Server Types > WebSphere® application servers > server_name > Container services > Dynamic cache service.

Enable servlet caching

The dynamic servlet cache service starts when servlet caching is enabled in Web Container panel.

Enable portlet caching

Start the dynamic portlet cache service by enabling servlet caching, then, enabling portlet fragment caching under Portlet Container panel.

Cache provider

Specifies whether to configure the server to use the dynamic cache or a stack product cache provider.

Avoid trouble: You can configure an alternate cache provider, if one is available. gotcha

Cache size

Specifies a positive integer as the value for the maximum number of entries that the cache holds.

Enter a cache size value in this field that is between the range of 100 through 200,000.

Default priority

Specifies the default priority for cache entries, determining how long an entry stays in a full cache.

Default 1
Range 1 to 255

Limit memory cache size

Specifies the size of the memory cache.

Use this feature to provide an ability to constrain the cache in terms of the JVM heap. In addition to specifying the cache size in MB, dynamic cache will also enable you to set a high watermark and low watermark for the cache heap that is consumed. When the cache heap memory reaches the high watermark, dynamic cache will either discard or be evicted from the disk using the least recently used (LRU) algorithm, until the cache is brought down to the low watermark. This functionality of limiting the cache in terms of the JVM heap is only available if the objects that are put into the cache implement the sizeable interface. This interface has one method that returns the size of the object in bytes put into the cache. Dynamic cache will use the sizeable interface to estimate the heap size of the cache.

Default -1 to disable limiting the memory cache size
Range 1 to maximum integer

Memory cache size

Specifies a value for the maximum memory cache size in megabytes (MB).

High threshold

Specifies a high watermark when the memory cache eviction policy starts. The threshold is expressed in terms of the percentage of the memory cache size in megabytes (MB). The default value is 95%

Values 1 to 100

Low threshold

Specifies a low watermark when the memory cache eviction policy ends. The threshold is expressed in terms of the percentage of the memory cache size in megabytes (MB). The default value is 80%.

Values 1 to 100

Enable disk offload

Specifies whether disk offload is enabled.

By default, the dynamic cache maintains the number of entries that are configured in memory. If new entries are created while the cache is full, the priorities that are configured for each cache entry, and a least recently used algorithm, are used to remove entries from the cache. In addition to having a cache entry removed from memory when the cache is full, you can enable disk offload to have a cache entry copied to the file system (the location is configurable). Later, if that cache entry is needed, it is moved back to memory from the file system.

Before you enable disk offload, consider the following:

Offload location

Specifies the location on the disk to save cache entries when disk offload is enabled.

If disk offload location is not specified, the default location, ${WAS_TEMP_DIR}/node/server name/_dynacache/cache JNDI name is used. If disk offload location is specified, the node, server name, and cache instance name are appended. For example, ${USER_INSTALL_ROOT}/diskoffload generates the location as ${USER_INSTALL_ROOT}/diskoffload/node/server name/cache JNDI name. This value is ignored if disk offload is not enabled.

The default value of the ${WAS_TEMP_DIR} property is ${USER_INSTALL_ROOT}/temp. If you change the value of the ${WAS_TEMP_DIR} property after starting WebSphere Application Server, but do not move the disk cache contents to the new location:
When you are specifying a directory, consider the following:

Flush to disk

Specifies if in-memory cached objects are saved to disk when the server is stopped. This value is ignored if Enable disk offload is not selected.

Default false

Limit disk cache size in GB

Specifies a value for the maximum disk cache size in GB. When you select this option, you can specify a positive integer value. Leaving this option blank indicates an unlimited size. This setting applies only if enable disk offload is specified for the cache.

Value 3 and above.

Limit disk cache size in entries

Specifies a value for the maximum disk cache size in number of entries. When you select this option, you can specify a positive integer value. Leaving this option blank indicates an unlimited size. This setting applies only if enable disk offload is specified for the cache.

Value 0 to MAXINT. A value of 0 indicates unlimited size.

Limit disk cache entry size

Specifies a value for the maximum size of an individual cache entry in MB. Any cache entry larger than this, when evicted from memory, will not be offloaded to disk. When you select this option, you can specify a positive integer value. Leaving this option blank indicates an unlimited size. This setting applies only if enable disk offload is specified for the cache.

Value 0 to MAXINT. A value of 0 indicates unlimited size.

Disk cache performance settings

Specifies the level of performance that is required by the disk cache. This setting applies only if enableDiskOffload is specified for the cache. Performance levels determine how memory resources should be used on background activity such as cache cleanup, expiration, garbage collection, and so on. This setting applies only if enable disk offload is specified for the cache.

High performance and high memory usage Indicates that all metadata will be kept in memory.
Balanced performance and balanced memory usage Indicates some metadata will be kept in memory. This is the default performance setting and will provide an optimal balance of performance and memory usage for most users.
Low performance and low memory usage Indicates that limited metadata will be kept in memory.
Custom performance Indicates that the administrator will explicitly configure the memory settings that will be used to support the above background activity. The administrator sets these values using the DiskCacheCustomPerformanceSettings object.

Disk cache cleanup frequency

Specifies a value for the disk cache cleanup frequency, in minutes. If this value is set to 0, the cleanup runs only at midnight. This setting applies only when the Disk Offload Performance Level is low, balanced, or custom. The high performance level does not require disk cleanup, and this value is ignored.

Value 0 to 1440

Maximum buffer for cache identifiers per metaentry

Specifies a value for the maximum number of cache identifiers that are stored for an individual dependency ID or template in the disk cache metadata in memory. If this limit is exceeded the information is offloaded to the disk. This setting applies only when the disk offload performance level is CUSTOM.

Value 100 to MAXINT

Maximum buffer for dependency identifiers

Specifies a value for the maximum number of dependency identifier buckets in the disk cache metadata in memory. If this limit is exceeded the information is offloaded to the disk. This setting applies only when the disk cache performance level is custom.

Value 100 to MAXINT

Maximum buffer for templates

Specifies a value for the maximum number of template buckets that are in the disk cache metadata in memory. If this limit is exceeded the information is offloaded to the disk. This setting applies only when the disk cache performance level is custom.

Value 10 to MAXINT

Disk cache eviction algorithm

Specifies the eviction algorithm that the disk cache will use to evict entries once the high threshold is reached. This setting applies only if enable disk offload is specified for the cache. This setting does not apply when the disk cache eviction policy is set to none.

None No eviction policy, so the disk cache can grow until it reaches its limit at which time the dynamic cache service stops writing to disk
Random When the disk size reaches a high threshold limit, the disk cache garbage collector wakes up and randomly picks entries on the disk and evicts them until the size reaches a low threshold limit.
Size When the disk size reaches a high threshold limit, the disk cache garbge collector wakes up and picks the largest entries on the disk and evicts them until the disk size reaches a low threshold limit.

High threshold

Specifies when the eviction policy runs. The threshold is expressed in terms of the percentage of the disk cache size in GB or entries. The lower value is used when limit disk cache size in GB and limit disk cache size in entries are specified. This setting does not apply when the disk cache eviction policy is set to none.

Values 1 to 100

Low threshold

Specifies when the eviction policy will end. The threshold is expressed in terms of the percentage of the disk cache size in GB or entries. The lower value is used limit disk cache size in GB and limit disk cache size in entries are specified. This setting does not apply when the disk cache eviction policy is set to none.

Values 1 to 100



Related concepts
Introduction: Dynamic cache
Related tasks
Task overview: Using the dynamic cache service to improve performance
[Fix Pack 5 or later] Configuring dynamic cache (DynaCache) to use the WebSphere eXtreme Scale dynamic cache provider
Related reference
cachespec.xml file
Reference topic    

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Last updated: Oct 20, 2010 11:50:58 PM CDT
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