cachespec.xml


 

+

Search Tips   |   Advanced Search

 

The dynamic cache service parses cachespec.xml when the server starts, and extracts a set of configuration parameters from each cache-entry element.

The cache-entry elements can be...

Cache entries in the root element are cached with the default cache instance. Cache entries in the <cache-instance> element are cached in that particular cache instance. Different cacheable objects have different class elements. We can define the specific object that a cache policy refers to using the name element.

 

Location

Place the cachespec.xml file with the deployment module.

We can also place a global cachespec.xml file in...

APP_ROOT/properties

The file...

appserver_root/properties/cachespec.dtd

...defines the legal structure and the elements that can be in the cachespec.xml file.

 

Usage notes

 

cache

The root element of cachespec.xml is cache and contains cache-instance and cache-entry elements. The cache-entry elements can also be placed inside of cache-instance elements to make that cache entry part of a cache instance that is different from the default.

 

cache-instance

<cache-instance name="cache_instance_name"></cache-instance>

The name attribute is the JNDI name of the cache instance that is set in the admin console.

Each cache-instance element must contain at least one cache-entry element. A cache entry that is matched within a cache-instance element is cached in the servlet cache instance specified by the name attribute. If identical cache-entry elements exist across cache-instance elements, the first cache-entry element that is matched is used.

 

cache-entry

Each cache entry must specify certain basic information that the dynamic cache uses to process that entry. This section explains the function of each cache entry element of the cachespec.xml file including:

With the current version of WAS, we can define multiple cache policies for a single servlet. For example, if we define multiple mappings for a servlet in web.xml, we can create a cache entry for each one of the mappings.

 

class

<class>command | servlet | webservice | JAXRPCClient | static | portlet </class>

This element is required and specifies how the appserver interprets the remaining cache policy definition. The value servlet refers to servlets and JSPs that are deployed in the WAS servlet engine. The webservice class extends the servlet with special component types for Web services requests. The JAXRPCClient is used to define a cache entry for the Web services client cache. The value, command, refers to classes using the WAS command model. The value, static, refers to files that contain static content.

The following examples illustrate the class element: 

<class>command</class>
<class>servlet</class>
<class>webservice</class>
<class>JAXRPCClient</class>
<class>static</class>
<class>portlet</class>

 

name

<name>name</name>

Use the following guidelines for the name element to specify a cacheable object:

Tip: The preferred location of the cachespec.xml file is in the Web app, not the properties directory.

We can specify multiple name elements within a cache-entry if we have different mappings that refer to the same servlet.

The following examples illustrate the name element: 

<name>com.mycompany.MyCommand.class</name>
<name>default_host:/servlet/snoop</name>
<name>com.mycompany.beans.MyJava Bean</name>  
<name>mywebapp/myjsp.jsp</name>
<name>/soap/servlet/soaprouter</name>
<name>http://remotecompany.com:9082/service/getquote</name>
<name>mywebapp/myLogo.gif</name>

 

sharing-policy

<sharing-policy> not-shared | shared-push | shared-pull | shared-push-pull</sharing-policy>

When working within a cluster with a distributed cache, these values determine the sharing characteristics of entries that are created from this object. If this element is not present, a not-shared value is assumed. In single server environments, not-shared is the only valid value. When enabling a replication, the default value is not-shared . This property does not affect distribution to Edge Side Include processors through the Edge fragment caching property.

Value

Description

not-shared Cache entries for this object are not shared among different appservers. These entries can contain non-serializable data. For example, a cached servlet can place non-serializable objects into the request attributes, if the <class> type supports it.
shared-push Cache entries for this object are automatically distributed to the dynamic caches in other appservers or cooperating JVMs. Each cache has a copy of the entry at the time it is created. These entries cannot store non-serializable data.
shared-pull Cache entries for this object are shared between appservers on demand. If an appserver gets a cache miss for this object, it queries the cooperating appservers to see if they have the object. If no appserver has a cached copy of the object, the original appserver runs the request and generates the object. These entries cannot store non-serializable data. This mode of sharing is not recommended.
shared-push-pull Cache entries for this object are shared between appservers on demand. When an appserver generates a cache entry, it broadcasts the cache ID of the created entry to all cooperating appservers. Each server then knows whether an entry exists for any given cache ID. On a given request for that entry, the appserver knows whether to generate the entry or pull it from somewhere else. These entries cannot store non-serializable data.

The following example shows a sharing policy:

<sharing-policy>not-shared</sharing-policy>

 

skip-cache

Takes the name of a request attribute, which if present in the request context, dictates that the response cannot be retrieved from the cache instance specified. Is useful for previewing content in production systems and verifying that the application is working and performing as expected. 

<cache>
    <!-- Applies only to the base cache -->
    <skip-cache-attribute>att1</skip-cache-attribute>    

    ...

    <cache-instance name="instance1">
       <!-- Applies only to this instance -->
       <skip-cache-attribute>att2</skip-cache-attribute> 
       ...
    </cache-instance>

</cache>

 

property

<property name="key">value</property>

...where key is the name of the property for this cache entry element, and value is the corresponding value.

We can set optional properties on a cacheable object, such as a description of the configured servlet. The class determines valid properties of the cache entry. At this time, the following properties are defined:

Property

Valid classes

Value

ApplicationName All Overrides the J2EEName application ID so that multiple applications can share a common cache ID namespace.
EdgeCacheable Servlet True or false. The default is false.

If true, then the given servlet or JSP file is externally requested from an Edge Side Include processor. Whether or not the servlet or JSP file is cacheable depends on the rest of the cache specification.

The permissible components for general edgecacheable cache entries are...

  • PARAMETER
  • HEADER
  • COOKIE
  • PATH_INFOSERVLET_PATH
ExternalCache Servlet
Portlet 		External cache name. The external cache name needs to match the external cache group name.
consume-subfragments Servlet
Web service
Portlet 		True or false. The default is false.

When a servlet is cached, only the content of that servlet is stored, and includes placeholders for any other fragments to which it includes or forwards. Consume-subfragments (CSF) tells the cache not to stop saving content when it includes a child servlet. The parent entry, the one marked CSF, includes all the content from all fragments in its cache entry, resulting in one big cache entry that has no includes or forwards, but the content from the whole tree of entries. Consume-subfragments can save a significant amount of appserver processing, but is typically only useful when the external HTTP request contains all the information needed to determine the entire tree of included fragments.

Use the <exclude> element to tell the cache to stop consuming for the excluded fragment and instead, create a placeholder for the include or forward.

For example, exclude A.jsp from the consume-subfragment, as follows: 

<property name="consume-subfragments">true
<exclude>/A.jsp<exclude>
</property>
do-not-consume Servlet
Web service
Portlet 		True or false. The default is false.

When a fragment parent has the consume-subfragment property set to true the child fragment content is saved in the cache entry of the parent. Do-not-consume (DNC) tells the cache to stop saving the content for this fragment in the parent cache-entry and create a placeholder instead for the include or forward.

alternate_url Servlet Alternate URL used to invoke the servlet or JSP file. The property is valid only if the EdgeCacheable property also is set for the cache entry.
persist-to-disk All True or false. The default is true.

When false, the cache entry is not written to the disk when overflow or server stopping occurs.

save-attributes Servlet
Portlet 		True or false. The default is true.

When false, the request attributes are not saved with the cache entry.Use the <exclude> element to specify the request attributes that do not apply to the save-attributes property. For example, to save only the attr1 attribute with the cache entry: 

<property name=
  "save-attributes">false
<exclude>attr1</exclude>
</property>

To save all attributes except the attr1 attribute in the cache entry, set the property to true in the preceding sample. If we do not use the <exclude> element, either all or no request attributes are saved with the cache entry.

delay-invalidations Command True or false.

When true, the commands that are invalidating cached objects based on the invalidation rules in this cache entry invalidate the cache entries after running. By default, the invalidation occurs before the command runs.

store-cookies Servlet
Portlet 		Takes one or more cookie name as its argument which is saved along with the cache object and restored by the servlet cache in the response with a set-cookie header. Save all cookies except cookie1 as part of the cache-entry as follows: 

<property name="store-cookies">true
<exclude>cookie</exclude>
</property>

Save only cookie1 as part of the cache-entry, as follows: 

<property name="store-cookies">false
<exclude><cookie1</exclude>
</property>
ignore-get-post Servlet
Portlet 		True or false. The default is false.

When true the request type is not appended to the cache-id for GET and POST requests unless the requestType component requestType component subelement is defined. By default the request type is automatically appended to the cache-id for GET and POST requests.

ignore-char-encoding Servlet
Portlet 		True or false. The default value is false.

When true, UTF-8 character encoding is not appended to the cache ID. Appending UTF-8 character encoding to the cache ID might lead to multiple copies of fragments, which unnecessarily increases the size of the cache.

do-not-cache Servlet
Portlet 		Defines a fragment that is neither cached nor consumed by its parent. 

<cache-entry>
...
<property name="do-not-cache">true</property>
or 

<cache-id>
<property name="do-not-cache">true</property>
</cache-id>
</cache-entry>

 

cache-id

To cache an object, the appserver must know how to generate a unique ID for different invocations of that object. These IDs are built either from user-written custom Java code or from rules defined in the cache policy of each cache entry. Each cache entry can have multiple cache ID rules that run in order until either:

If none of the cache ID generation rules produce a valid cache ID, the object is not cached.

Each cache-id element defines a rule for caching an object and is composed of the sub-elements component, timeout, inactivity, priority, property, idgenerator, and metadatagenerator.

The following example illustrates a cache-id element: 

<cache-id>
   component*| timeout? | inactivity? | priority? | property* | idgenerator? | metadatagenerator?
</cache-id>

 

component subelement

Use the component subelement to generate a portion of the cache ID. The component subelement consists of the attributes id, type, and ignore-value, and the elements index, method, field, required, value, and not-value.

Use the id attribute to identify the component.

Use the type attribute to identify the type of component.

The following table lists the values for the type.

Type Valid classes Meaning
method Command Calls the indicated method on the command or object
field Command Retrieves the named field in the command or object
parameter Servlet
Portlet 		Retrieves the named parameter value from the request object
parameter-list Servlet
Portlet 		Retrieves a list of values for the named parameter
session Servlet
Portlet 		Retrieves the named value from the HTTP session
cookie Servlet Retrieves the named cookie value
attribute Servlet
Portlet 		Retrieves the named request attribute
header Servlet
Web service
Portlet 		Retrieves the named request header
pathInfo Servlet Retrieves the pathInfo element from the request
servletpath Servlet Retrieves the servlet path
locale Servlet
Portlet 		Retrieves the request locale

The locale component is permissible for edgecacheable entries only, when using RRD. The locale component is not valid for all other ESI versions.

requestType Servlet
Portlet 		Retrieves the HTTP request method from the request.

The requestType component is permissible for edgecacheable entries only, when using RRD. The requestType component is not valid for all other ESI versions.

tiles_attribute Servlet
Portlet 		Retrieves the value of an attribute from a tile.
SOAPEnvelope Web service
Web services client cache 		Retrieves the SOAPEnvelope element from a Web services request. An ID attribute of Hash uses a Hash of the SOAPEnvelope element, while Literal uses the SOAPEnvelope element as received.
SOAPAction Web service Retrieves the SOAPAction header, if available, for a Web services request.
serviceOperation Web service Retrieves the service operation for a Web services request
serviceOperationParameter Web service Retrieves the specified parameter from a Web services request
operation Web services client cache Indicates an operation type in the WSDL file. The id attribute is ignored and the value is the operation or method name. If the namespace of the operation is specified, format the value as namespaceOfOperation:nameOfOperation
part Web services client cache Indicates an input message part in the WSDL file or a request parameter. Its id attribute is the part or parameter name, and the value is the part or parameter value.
SOAPHeaderEntry Web services client cache Retrieves special information in the SOAP header of the Web services request. The id attribute specifies the name of the entry. In addition, the entry of the SOAP header in the SOAP request must have the actor attribute, which contains com.ibm.websphere.cache. For example: 

<soapenv:Header>
    <getQuote soapenv:actor="com.ibm.websphere.cache">IBM</getQuote>
</soapenv:Header>
portletSession Portlet Retrieves the named value from the portlet session
portletWindowId Portlet Retrieves the portlet window ID from the portlet request object
portletMode Portlet Retrieves the portlet mode from the portlet request object
portletWindowsState Portlet Retrieves the portlet window state from the portlet request object
sessionID Servlet
Portlet 		Retrieves the HTTP session ID

Use the ignore-value attribute to specify whether or not to use the value that is returned by this component in cache ID formation. This attribute is optional with a default value of false. If the value is true, only the ID of the component is used when creating a cache ID, or no output is used when creating a dependency or invalidation ID.

Use the method element to call a void method on a returned object. You can infinitely nest method and field objects in any combination. The method must be public and is not valid for edge-cacheable components. For example: 

<component id="getUser" 
           type="method">

    <method>getUserInfo
        <method>getName</method>
    </method>

</component>

This method is equivalent to getUser().getUserInfo().getName()

For component types attribute, method, or field that can return an object, when the object returned is a collection or array, the ID is created with a comma separated list of the elements in the collection or array. For example, if the request attribute users returns an array [a, b] and the cache entry is defined like the following example: 

<cache-entry>
    <class>servlet</class>
    <name>xxx.jsp</name>
    <cache-id>
        .
        .
        <component id="users" type="attribute">
            <required>true</required>
        </component>
        .
        .
    </cache-id>
    <dependency-id>dep
        <component id="users" type="attribute">
            <required>true</required>
        </component>
    </dependency-id>
</cache-entry>
The cache id contains the string users: a,b.

The dependency id is dep: a,b.

Use the multipleIDs attribute with the component types to specify and generate multiple dependency IDs (or invalidation IDs), based on the items in the collection or array. For example: 

<cache-entry>
    <class>servlet</class>
    <name>xxx.jsp</name>
    <cache-id>
        .
        .
            <component id="users" type="attribute">
                <required>true</required>
            </component>
        .
        .
    </cache-id>
    <dependency-id>dep
        <component id="users" type="attribute" multipleIDs="true">
            <required>true</required>
        </component>
    </dependency-id>
</cache-entry>
The cache policy will generates the following dependency IDs:

Use the index element with the prvious component type to add only the value of the element at the specified index position in the collection or array, to the ID that is being created. 

<cache-entry>
    <class>servlet</class>
    <name>xxx.jsp</name>
    <cache-id>
        .
        .
            <component id="users" type="attribute">
                <required>true</required>
                <index>1</index>
            </component>
        .
        .
    </cache-id>
    <dependency-id>dep
        <component id="users" type="attribute" multipleIDs="true">
            <required>true</required>
        </component>
    </dependency-id>
</cache-entry>
The previous cache policy generates the following component to use in the cache ID: users: b. Use the <method> element to call a void method on a returned object.

Use the field element to access a field in a returned object. We can infinitely nest method and field objects in any combination. The field must be public. This field is not valid for edge-cacheable components. For example: 

<component id="getUser" type="method"><method>getUserInfo
<field>name</field></method></component>

This method is equivalent to the getUser().getUserInfo().name method.

Use the required element to specify whether or not this component must return a non-null value for this cache ID to represent a valid cache. If set to true, this component must return a non-null value for this cache ID to represent a valid cache ID. If set to false, the default, a non-null value is used in the formation of the cache ID and a null value means that this component is not used at all in the ID formation. For example: 

<required>true</required>

Use the value element to specify values that must match to use this component in cache ID formation. For example: 

<component id="getUser" type="method"><value>blue</value> 
<value>red</value> </component>

Use the not-value element to specify values that must not match to use this component in cache ID formation. This method is similar to value element, but instead prescribes the defined values from caching. Use multiple not-value elements when more than one value not valid exists. For example: 

<component id="getUser" type="method">
<required>true</required>
<not-value>blue</not-value>
<not-value>red</not-value></component>

The component subelement can have either a method and a field element, a value element, or a not-value element. The method and field elements apply to commands only.

The following example illustrates the attributes of a component sub-element: 

<component id="isValid" type="method" ignore-value="true"><component>

 

timeout subelement

The timeout subelement is used to specify an absolute time-to-live (TTL) value for the cache entry. For example, 

<timeout>value</timeout>

where value is the amount of time, in seconds, to keep the cache entry. Cache entries that are in memory are kept indefinitely, as long as the entries remain in memory. Cache entries that are stored on disk are evicted if they are not accessed for 24 hours.

 

inactivity subelement

The inactivity subelement is used to specify a time-to-live (TTL) value for the cache entry based on the last time that the cache entry was accessed. It is a subelement of the cache-id element. 

<inactivity>value</inactivity>
where value is the amount of time, in seconds, to keep the cache entry in the cache after the last cache hit.

 

priority subelement

Use the priority subelement to specify the priority of a cache entry in a cache. The priority weighting is used by the least recently used (LRU) algorithm of the cache to decide which entries to remove from the cache if the cache runs out of storage space. For example, 

<priority>value</priority>

where value is a positive integer between 1 and 16 inclusive.

 

Samples

The following sample keeps the cache entry in the cache for a minimum of 35 seconds and a maximum of 180 seconds. If the cache entry is accessed within each 35 second inactivity period, the inactivity period is extended for another 35 seconds. However, because the timeout element is also configured, the cache entry is always invalidated after 180 seconds. If the cache entry is not accessed within the 35 second period, the entry is removed from the cache. 

<cache-id>
    <component id="timeout" type="parameter">
        <required>true</required>
    </component>
    <timeout>180</timeout>
    <inactivity>35</inactivity>
    <priority>1</priority>
</cache-id>

The following sample keeps the cache entry in the cache for a minimum of 600 seconds. If the cache entry is accessed within each 600 second period, the inactivity period is extended for another 600 seconds. If the cache entry is not accessed within the 600 second period, the cache entry is removed from the cache. 

<cache-id>
    <component id="timeout" type="parameter">
        <required>true</required>
    </component>
    <inactivity>600</inactivity>
    <priority>1</priority>
</cache-id>

In the following sample, the value for inactivity has no meaning because the timeout period is less than the inactivity period. The cache entry is always invalidated after 180 seconds, no matter how often the cache entry is accessed. 

<cache-id>
    <component id="timeout" type="parameter">
        <required>true</required>
    </component>
    <timeout>180</timeout>
    <inactivity>600</inactivity>
    <priority>1</priority>
</cache-id>

 

property subelement

Use the property subelement to specify generic properties for the cache entry. For example, 

<property name="key">value</property>

where key is the name of the property to define, and value is the corresponding value.

For example: 

<property name="description">The Snoop Servlet</property>

Property

Valid classes

Meaning

sharing-policy/timeout/priority All Overrides the settings for the containing cache entry when the request matches this cache ID.
EdgeCacheable Servlet Overrides the settings for the containing cache entry when the request matches this cache ID.

 

idgenerator and metadatagenerator sub-elements

Use the idgenerator element to specify the class name that is loaded for the generation of the cache ID. The IdGenerator element must implement the com.ibm.websphere.servlet.cache.IdGenerator interface for a servlet or the com.ibm.websphere.webservices.IdGenerator interface for the Web services client cache. An example of the idgenerator element follows: 

<idgenerator> class name </idgenerator>

Where class name is the fully-qualified name of the class to use. Define this generator class in a shared library.

Use the metadatagenerator element inside the cache-id element to specify the class name loaded for the metadata generation. The MetadataGenerator class must implement the com.ibm.websphere.servlet.cache.MetaDataGenerator interface for a servlet or the com.ibm.websphere.cache.webservices.MetaDataGenerator interface for Web services client cache. The MetadataGenerator class defines properties like timeout, inactivity, external caching properties or dependencies. An example of the metadatagenerator element follows: 

<metadatagenerator> classname </metadatagenerator>
In this example, class name is the fully-qualified name of the class to use. Define this generator class in a shared library.

 

dependency-id element

Use the dependency-id element to specify additional cache identifiers that associate multiple cache entries to the same group identifier.

The value of the dependency-id element is generated by concatenating the dependency ID base string with the values that are returned by its component elements. If a required component returns a null value, the entire dependency does not generate and is not used. Validate the dependency IDs explicitly through the dynamic cache API, or use the invalidation element. Multiple dependency ID rules can exist in one cache-entry element. All dependency rules run separately.

 

invalidation element

To invalidate cached objects, the appserver must generate unique invalidation IDs. Build invalidation IDs by writing custom Java code or through rules defined in the cache policy of each cache entry.

The following example illustrates an invalidation in the cache policy: 

<invalidation>component* | invalidationgenerator? </invalidation>

 

invalidationgenerator subelement

The invalidationgenerator element is used with the Web Services client cache only. Use the invalidationgenerator element to specify the class name to load for generating invalidation IDs. The InvalidationGenerator class must implement the com.ibm.websphere.cache.webservices.InvalidationGenerator interface. An example of the invalidationgenerator element follows: 

<invalidationgenerator>class name</invalidationgenerator>
In this example, classname is the fully qualified name of the class that implements the com.ibm.websphere.cache.webservices.InvalidationGenerator interface. Define this generator class in a shared library.


 

Related tasks

Set cacheable objects with the cachespec.xml file

 

Related

Example: Set the dynamic cache service