Servlet cache instance settings

Servlet cache instance settings

A servlet cache instance is a location, in addition to the default shared dynamic cache, where dynamic cache can store, distribute, and share data. By using servlet cache instances, the applications have greater flexibility and better tuning of the cache resources. The JNDI name specified for the cache instance is mapped to the name attribute in the <cache-instance> tag in the cachespec.xml configuration file.

From the admin console, click...
Resources > Cache instances > Servlet cache instances > cache_instance_name.

Name

Required display name for the resource.

JNDI name

JNDI name for the resource. Specify this name in the name attribute field in the <cache-instance> tag in the cachespec.xml configuration file. This tag is used to find the particular cache instance in which to store cache entries.

Description

Description for the resource. This field is optional.

Category

Category string to classify or group the resource. This field is optional.

Cache size

Positive integer for the maximum number of entries the cache holds. The cache size is usually in the thousands.

Information Value
Default 2000
Range 100 - no set maximum value

Default priority

Default priority for servlets that can be cached. This value determines how long an entry stays in a full cache.

The recommended value is one.

Enable disk offload

Specifies if disk offloading is enabled.

If we have disk offload disabled, when a new entry is created while the cache is full, the priorities are configured for each entry and the least recently used algorithm are used to remove the entry from the cache in memory. If we enable disk offload, the entry that would be removed from the cache is copied to the local file system. The location of the file is specified by the disk offload location.

To improve disk offload performance, use only one hard drive for each JVM.

Information Value
Default false

Offload location

Directory used for disk offload.

If disk offload location is not specified, the default location, ${WAS_TEMP_DIR}/node/server name/_dynacache/cache JNDI name will be 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 new disk cache file at the new disk offload location.
If the Flush to disk setting is enabled, all the disk cache content at the old location is lost when restarting the Application Server

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

Maximum disk cache size in GB. When selected, 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 size in entries

Maximum disk cache size in number of entries. When selected, 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

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 selected, 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.

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 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 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

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.

Information Value
Value 0 to 1440

Maximum buffer for cache identifiers per metaentry

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

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

Maximum number of template 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 10 to MAXINT

Eviction policy algorithm

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.

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 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 starts. The threshold is expressed in terms of the percentage of the disk cache size in GB or entries. The disk cache garbage collector is awaken when the disk size exceeds high threshold limit. The lower value limits disk cache size in GB and disk cache size in entries. 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 limits disk cache size in GB and disk cache size in entries. The disk cache garbage collector, when awaken, evicts entries until the disk size reaches the low threshold limit. 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 enable sharing of cache IDs, cache entries, and cache invalidations with other servers in the same replication domain.

This option might be unavailable for cache instances created with a previous version of WAS.

Full group replication domain

Replication domain from which the data is replicated.

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 administrative console by clicking Environment > Internal replication domains > New. The replication domain we 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

The global sharing policy for this cache instance.

In multiple-server environments, 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 will retrieve the content from the publishing server. If a request is made for an ID which has not been previously published, the server assumes it does not exist in the cluster and creates a new entry.
Pull only shares cache entries for this object between application servers on demand. If an application server gets a cache miss for this object, it queries the cooperating application servers to see if they have the object. If no application server has a cached copy of the object, the original application server runs the request and generates the object. These entries cannot store non-serializable data. This mode of sharing is not recommended.
Push only sends the cache ID and cache content of new content to all other servers in the replication domain.
The sharing policy of Not Shared results in the cache ID and cache content not being shared with other servers in the replication domain.

The default setting for a single-server environment without clustering is Not Shared.

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).

Use the DistributedMap and DistributedObjectCache interfaces for the dynamic cache
Object cache instance collection
Object cache instance settings
Servlet cache instance collection

Information	Value
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	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.

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