Dynamic cache service settings

Dynamic cache service settings

To configure and manage the dynamic cache service settings...
Servers | Server Types | WebSphere application servers | server_name | Container services | Dynamic cache service

Enable service at server startup

The dynamic servlet cache service starts when the server starts.
This option displays on WebSphere Application Server V6.1 servers but is not available on WebSphere Application Server V7.0 servers.

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

Whether to configure the server to use the default dynamic cache provider or an alternate cache provider. If an alternate cache provider, such as WebSphere eXtreme Scale, is available, it appears in the list of available cache providers.

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

Default priority for cache entries, determining how long an entry stays in a full cache.

Information Value
Default 1
Range 1 to 255

Limit memory cache size

Size of the memory cache.
Use this feature to constrain the cache in terms of the JVM heap. In addition to specifying the cache size in MB, dynamic cache also enables 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 either discards or is 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 uses the sizeable interface to estimate the heap size of the cache.

Information Value
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%

Information Value
Values 1 to 100

Low threshold

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%.

Information Value
Values 1 to 100

Enable disk offload

Whether disk offload is enabled.
By default, the dynamic cache maintains the number of entries configured in memory. If new entries are created while the cache is full, the priorities 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, we 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:

We cannot specify the number of cache entries that are offloaded to disk.

We cannot specify the amount of disk space to use.

Offload location

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 we 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:

The application server creates a disk cache file at the new disk offload location.

If the Flush to disk setting is enabled, all of the disk cache content at the old location is lost when you restart the application server

When you are specifying a directory, consider the following:

(dist) If we expect to cache many objects or large objects that will be around for some time, consider using a separate disk drive if you are using Windows operating systems, or a separate file system if you are using UNIX platforms.

If we use the default directory and the disk fills up, WebSphere Application Server could possibly stall if it must write messages to log files, and there is no more space.

If we specify a directory such as /tmp on UNIX platforms and that directory fills up, we might have trouble logging on to the system.

Depending on the operating system, you might see disk full messages on the console.

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.

Information Value
Default false

Limit disk cache size in GB

Specifies a value for the maximum disk cache size in GB. When you select this option, we 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.

Information Value
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, we 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.

Information Value
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 value, when evicted from memory, is not offloaded to disk. When you select this option, we 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.

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

Disk cache performance settings

Level of performance 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.

Information Value
High performance and high memory usage Indicates that all metadata is kept in memory.
Balanced performance and balanced memory usage Indicates some metadata is kept in memory. This is the default performance setting and provides an optimal balance of performance and memory usage for most users.
Low performance and low memory usage Indicates that limited metadata is kept in memory.
Custom performance Indicates that the administrator explicitly configures the memory settings 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 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.

Information Value
Value 0 to 1440

Maximum buffer for cache identifiers per metaentry

Specifies a value for the maximum number of cache identifiers 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.

Information Value
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.

Information Value
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.

Information Value
Value 10 to MAXINT

Disk cache eviction algorithm

Eviction algorithm that the disk cache uses to evict entries when 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.

Information Value
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 garbage 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.

Information Value
Values 1 to 100

Low threshold

Specifies when the eviction policy ends. 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.

Information Value
Values 1 to 100

Enable cache replication

Use cache replication to have cache entries copied to multiple application servers configured in the same replication domain.

Full group replication domain

Specifies a replication domain from which the data is replicated.
Choose from any replication domains that have been defined. If there are no replication domains listed, create one during cluster creation or manually in the console by clicking...
Environment | Internal replication domains | New

The replication domain you choose to use with the dynamic cache service must be using a Full group replica. Do not share replication domains between replication consumers. Dynamic cache should use a different replication domain from session manager or stateful session beans.

Replication type

Specifies the global sharing policy for this application server.
The following settings are available:

Both push and pull sends the cache ID of newly updated content to other servers in the replication domain.
Then, if one of the other servers requests the content, and that server has the ID of the cache entry for the previously updated content, it retrieves the content from the publishing server. Alternatively, if a request is made for an ID which has not been previously published, the server assumes that it does not exist in the cluster and creates an entry.

Push only sends the cache ID and cache content of new content to all other servers in the replication domain.

When you use the Not Shared setting, as cache entries are created, neither the cache content nor the cache IDs are propagated to other servants or servers in the replication domain. However, invalidations are propagated to other servants or servers. We can set the sharing policy at different levels. A global sharing policy, which is the default policy for all caches, is defined when you configure the dynamic cache service. We can overwrite this sharing policy by modifying the cachespec.xml file. Additionally, we can overwrite the sharing policy at the API level when cache entries are being created.
The default is Not Shared.
When Not Shared is selected, you see none in the cachespec.xml file.

Push frequency

Time, in seconds, to wait before pushing new or modified cache entries to other servers.
If we set this property value to 1 (one) or greater, the application server pushes all cache entries created or modified during the time period to other servers. If we set the property to 0 (zero) or a negative value, the application server converts the property value to the default value, which is 1 (one).

Related concepts
Introduction: Dynamic cache
Task overview: Use the dynamic cache service to improve performance
cachespec.xml file

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

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

Information	Value
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 garbage collector wakes up and picks the largest entries on the disk and evicts them until the disk size reaches a low threshold limit.