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Caching


  1. Overview
  2. Caching pages shared by multiple users
  3. cookie.ignore.regex parameter
  4. Cache scope
  5. Expiry time
  6. Cache scope and expiry time settings
  7. Default cache scope and expiry time settings
  8. Factors affecting cache scope and expiry time
  9. Limitations
  10. Security Issues
  11. Troubleshooting


After you have reviewed this content, you should also review the WebSphere Portal and Web Content Manager Performance Tuning Guide.


Caching pages shared by multiple users

If we use a proxy server such as WebSphere Edge Server, and your system has content that can be shared among multiple users, we can improve performance by caching this shared content.

The cache scope and cache expiry time are configured by page, portlet, and theme. WebSphere Portal combines this information to produce a final cache scope and expiry time for each page it serves. Configure these cache settings in one of the following two ways:


cookie.ignore.regex parameter

Add the cookie.ignore.regex parameter to the portal resource environment provider:

  1. Start the WebSphere_Portal server.

  2. Log in to the WAS admin console and go to...

      Resources | Resource Environment | Resource Environment Providers | WP ConfigService | Additional Properties | Custom Properties | New

  3. Name of the required property and set the value of the property to the appropriate value as required.

    To specify cookies that are NOT included in the digest computation, specify...

      cookie.ignore.regex = digest\\.ignore.*|Item1|Item2|Item3|Item4,

    ...where Item1, Item2, Item3, Item4 are the items to exclude from getting cachedDefault is...

      digest\\.ignore.*|LtpaToken|LtpaToken2|JSESSIONID

    Any cookie set or modified by any component causes the digests in the URL to change, directly affecting the cache of those resources. If a particular cookie is required for some custom code or feature to work but it is not designed to invalidate the caches that cookie name should be included in the cookie.ignore.regex list or at least matched successfully by the regular expression is that property. This process ensures that changes to the cookie value do not have any adverse impact on performance by prematurely invalidating cache entries.

  4. Click Apply and save the changes.

  5. Log out of the WAS admin console.

  6. Restart the WebSphere_Portal server.


Cache scope

The cache scope determines where the content will be cached. There are two types of caching:

Shared cache across users This type of caching provides the biggest performance improvement. A proxy server caches content and serves requests for the content. This caching eases the load on the server because requests that are served by the proxy do not reach WebSphere Portal. If most requests are for customized content, this type of caching provides no performance improvement. The following default values exist for portlet definitions and themes if nothing is provided:

This type of caching should be used only for pages containing public content that is not personalized.

  • Remote cache scope is non-shared
  • Remote cache expiry is 0 seconds
Non-shared cache for a single user (Web browser cache) This type of caching provides a much smaller performance improvement. The cache is typically located in each user's Web browser. This type of caching can be used for all content, including content that is personalized. If the computer is shared among multiple users, a user may see personalized content from other users if served from the browser cache. To prevent this from happening, do not enable private caching, even for personalize content.


Expiry time

The expiry time determines how long the page is stored in a cache. WebSphere Portal allows three options for specifying expiry time:

Cache always expires The content will never be cached in either a shared or a private cache; set the remote cache expiry to 0
Cache never expires The content can be stored indefinitely in either a shared or a private cache; set the remote cache expiry to -1
Cache expires after this many seconds The content will be stored for the number of seconds specified in either a shared or a private cache; set the remote cache expiry to a positive integer up to 2^31 -1


Cache scope and expiry time settings

Remote cache information on a Page

Contributes Key Possible Values Set Via XML Access Set Via UI
remote cache scope com.ibm.portal.remote-cache-scope SHARED, NON_SHARED yes yes
remote cache expiry com.ibm.portal.remote-cache-expiry Time in seconds, given as an integer between -1 and the value ((2 to the power of 31)-1)

Use the value -1 if you never want the cache to expire.

yes yes
Ignore Access Control in Caches com.ibm.portal.IgnoreAccessControlInCaches True, False yes yes

Example for XML access: 

 <parameter update="set" name="com.ibm.portal.remote-cache-scope" type="string">SHARED</parameter>
 <parameter update="set" name="com.ibm.portal.remote-cache-expiry" type="string">3000</parameter>
 <parameter update="set" name="com.ibm.portal.IgnoreAccessControlInCaches" type="string">true</parameter>


Remote cache information for Themes

Contributes Key Possible Values Set Via XML Access Set Via UI
remote cache scope com.ibm.portal.remote-cache-scope SHARED, NON_SHARED yes no
remote cache expiry com.ibm.portal.remote-cache-expiry Time in seconds, given as an integer between -1 and the value ((2 to the power of 31)-1)

Use the value -1 if you never want the cache to expire.

yes no

Example for XML access: 

 <parameter update="set" name="com.ibm.portal.remote-cache-scope" type="string">SHARED</parameter>
 <parameter update="set" name="com.ibm.portal.remote-cache-expiry" type="string">3000</parameter>


Remote cache information on a Portlet Definition

Contributes Key Possible Values Set Via deployment descriptors or an extension to it Set Via UI
remote cache scope remote-cache-scope SHARED, NON_SHARED yes no
expiration cache EXPIRATION_CACHE Time in seconds, given as an integer between -1 and the value ((2 to the power of 31)-1)

Use the value -1 if you never want the cache to expire.

yes yes
remote cache dynamic remote-cache-dynamic True, False yes no

The Standard Portlet API specification defines the meaning of the EXPIRATION_CACHE value. WebSphere Portal uses this value to determine the lifetime of the portlet's output in a remote cache, just like the remote cache expiry for themes. The remote cache dynamic setting is an optimization to notify the container whether a portlet window can publish remote cache information at render time. The deployment descriptors specification shows how to deal with these settings.

Overall remote cache information on a Portlet Window:

Contributes Key Possible Values Set Via deployment descriptors or an extension to it Set Via UI
remote cache scope remote-cache-scope SHARED, NON_SHARED no, only published during render time no
expiration cache EXPIRATION_CACHE Time in seconds, given as an integer between -1 and the value ((2 to the power of 31)-1)

Use the value -1 if you never want the cache to expire.

no, only published during render time no

The portlet definition describes the portlet at a deployment time level given in the portlet deployment descriptors. Thus, attributes specified in the deployment descriptors are valid on all occurrences on all pages of this portlet. The portlet window describes the runtime entity for a portlet. While in the rendering phase of a portlet, the portlet can publish values or attributes via an API. Thus, attributes specified while rendering the portlet is portlet instance specific.

Example code snippet for publishing the information at render time: 

 String paramExpiry = "3000";
 String paramScope = "SHARED";
 renderResponse.setProperty( "portlet.remote-cache-scope", paramScope );
 renderResponse.setProperty( RenderResponse.EXPIRATION_CACHE, paramExpiry );


Remote cache information on Portlet Wide Settings

that contribute to the overall remote cache information on portlet
Contributes Key Possible Values Set Via XML Access Set Via UI
remote cache expiration remote.cache.expiration Time in seconds, given as an integer between -1 and the value ((2 to the power of 31)-1)

Use the value -1 if you never want the cache to expire.

no, property in WP NavigatorService no
vary vary List of HTTP header fields that can be put into the vary response header no, property in WP NavigatorService no


Default cache scope and expiry time settings

WP NavigatorService settings:

Key Meaning Default value
public.session Whether an anonymous user always has a public session. Useful when a portlet requires a session for anonymous users. To enable public sessions for pages that anonymous users can view without logging in, set this parameter to true. Setting public.session influences the remote cache scope for public pages. If public.session is set to true, then the cache scope is set to non-shared (private). If public.session is set to false, then the cache scope is set to shared (public).

Setting public.session to true might reduce performance.

false
public.expires Cache expiration time (in seconds) for caches outside of WebSphere Portal and for unauthenticated pages only. These caches must adhere to the HTTP 1.1 specification (RFC 2616). The public.expires key specifies the time after which HTTP caches should drop the response. This can be further restricted by the remote.cache.expiration key. This value is used as a maximum value for the cache expiration time and as a global default value for unauthenticated pages. If the setting remote.cache.expiration is also set to a value greater than or equal to 0, the smaller one of the two values is used.

WebSphere Portal calculates and aggregates the remote cache informatione that is the scope and expiration time, by a number of parameters contributed by themes, pages, and portlets besides the settings described here. Therefore WebSphere Portal can do any of the following internally while processing a request:

  • Reduce the cache lifetime
  • Reduce the cache scope, for example, from public (shared) to private (non-shared)
  • Switch off the overall cachability of pages.

Therefore this value might not be static for all responses resulting from requests to unauthenticated pages. The response of WebSphere Portal sets the following header fields:

  • The Expires header with the expiration time added to the system date and time.
  • The Cache-Control : max-age = header with the expiration time as its parameter.

The default setting specified in this file is 60 seconds. If no value is specified, WebSphere Portal defaults the value to 60 seconds.

60 (sec)
remote.cache.expiration Maximum cache lifetime (in seconds) of a page, both public and private. Use this setting to specify a global value for the expiration of pages in remote caches. Setting this value to 0 switches caching off in remote caches. If the legacy setting is not available, this setting is used for authenticated and unauthenticated pages. If the legacy setting is available, then the smaller of the two values is used for unauthenticated pages only. In this case the remote.cache.expiration setting is used for authenticated pages in general. If theme, composition, and portlets contribute remote cache information, then the global settings also contribute to the information. In this case the lowest of the values of all contributors is used, including the global settings. The default setting specified in this file is 60 seconds. If no value is specified, WebSphere Portal defaults the value to zero (0 seconds). 0 (sec)
remoteCacheInfo.response.header.vary HTTP headers that force a proxy to cache different variants of the same URL. Use this setting to specify a comma separated list of HTTP header fields to which WebSphere Portal should refer in its vary field of the generated HTTP response. This is required to ensure that proxy caches can invalidate entries in their cache if the specified header fields do not match from request to request. User-Agent
public.cache-control Value set for the cache-control HTTP header field when the portal generates a response in request for public pages. This header field controls the behavior of all caching mechanisms along the request/response chain. no-cache
private.cache-control Value set for the cache-control HTTP header field when the portal generates a response in request for private pages. This header field controls the behavior of all caching mechanisms along the request/response chain. no-cache


Factors affecting cache scope and expiry time

Multiple factors can affect the cache scope and expiry time for a page. The remote-cache-scope and remote-cache-expiration of a rendered page view is calculated as the minimum of the following factors:


Limitations

With the previous settings, it is possible to generate an HTTP response header like Cache-Control: max-age=-1, which indicates an unlimited cache expiration when a page is rendered. This is beyond the HTTP 1.1 specification but if a proxy cache does not support an unlimited cache expiration, WebSphere Portal supports it. If the cache infrastructure does not properly work with this response header, set the remote.cache.expiration value in the WP NavigatorService to a large value. To set an unlimited cache expiration is not possible if the cache infrastructure does not support it.


Security Issues

Storing authenticated pages in a shared cache introduces security holes. If a malicious user discovered the URL for an authenticated pages that user could read pages containing private information. By default, WebSphere Portal does not permit shared caching for authenticated pages. We can use the Properties portlet or xmlaccess.sh to override these default settings using the parameter...

...but in most cases this is not recommended.

In some rare circumstances, it might be useful to store authenticated pages in a shared cache.

For example, if all authenticated users receive identical content, then storing authenticated pages in a shared cache might be acceptable.


Troubleshooting

In general, you should monitor the cache hit rate on the proxy server and adjust the cache size appropriately. If the hit rate is not what you expected, increase the cache size. We can also check the following item:


Parent: Configure portal behavior


Related:
Set service configuration properties
Portal configuration services
Portal farm considerations