Portal Caching

 

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

See also: Tuning Guide

 

Cache pages shared by multiple users

We can configure...

  • cache scope
  • cache expiry time

...for...

  • pages
  • portlets
  • themes

...using...

When caching JSR portlets, the cache scope is only for proxy server caching policies and requires the use of an edge server cache. Local display caching policies are not affected by this setting. The cache expiration setting is used for both local and remote caching policies.

 

Cache scope

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

  • Public or shared cache

    This type of caching provides the biggest performance improvement. A proxy server caches portal content and serves requests for the content. This caching eases the load on the portal server because requests that served by the proxy do not reach the portal. If most requests are for customized content, this type of caching provides no performance improvement. This type of caching should be used only for pages that contain public content that is not personalized. The following default values exist for portlet definitions, themes, and compositions if nothing is provided:

    • Remote cache scope is non-shared
    • Remote cache expiry is 0 seconds

  • Private cache (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

The following table lists the portal resources that contribute to the overall remote cache information on a page.

Resource Contributes Key Possible Values Set Via XML Access Set Via UI
Page 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 IgnoreAccessControlInCaches True, False yes yes

Example for XML access:

    <parameter name"com.ibm.portal.remote-cache-scope">SHARED</parameter>
    <parameter name"com.ibm.portal.remote-cache-expiry">3000</parameter>
    <parameter name"IgnoreAccessControlInCaches">true</parameter>

Resource Contributes Key Possible Values Set Via XML Access Set Via UI
Themes 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 name"com.ibm.portal.remote-cache-scope">SHARED</parameter>
    <parameter name"com.ibm.portal.remote-cache-expiry">3000</parameter>

Resource Contributes Key Possible Values Set Via deployment descriptor or an extension to it Set Via UI
Portlet Definition 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 descriptor specification shows how to deal with these settings.

Resource Contributes Key Possible Values Set Via deployment descriptor or an extension to it Set Via UI
Portlet Window 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 descriptor. Thus, attributes specified in the deployment descriptor 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( RemoteCacheInfo.KEY_SCOPE, paramScope );
    renderResponse.setProperty( RenderResponse.EXPIRATION_CACHE, paramExpiry );

Resource Contributes Key Possible Values Set Via XML Access Set Via UI
Portal Wide Settings 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

The following table shows possible WP NavigatorService settings:

Key Meaning Default value
public.session Specifies whether an anonymous user always has a session, which may be useful when a portlet requires a session for anonymous users.

Setting public.session to true reduces portal performance.

false
public.expires Specifies the cache expiration time (in seconds) for the unpersonalized portal page. 60 sec
public.reload Specifies the time (in seconds) that unauthenticated pages reload. 60 sec
remote.cache.expiration Specifies the maximum cache lifetime of any page (both public and private). 60 sec
vary Specifies the HTTP headers that force a proxy to cache different variants of the same URL. Accept-Language user-Agent

 

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:

  • Cache scope and expiry time specified for the page

  • Cache scope and expiry time of the portlets on the page

    If any of the portlets on a page can only be cached in a private cache, then the entire page can only be cached in a private cache. A page cannot be stored in a shared cache unless all portlets on the page can also be stored in a shared cache. Make sure cache settings for portlets and pages are consistent.

  • Cache scope and expiry time of the theme

  • Global values as defined in the Navigator Service in the IBM WAS Administrative Console. For details about how to set these values refer to Setting configuration properties.

 

Limitations

  • For best results, use WAS Edge Components version 6.0.0.1 (or later), v5.1.0.7 (or later), v5.0.2.30 (or later) for the proxy server. Previous versions do not serve multiple markup types from the same cache. If there are multiple requests for the same page, but with different markup, the cache is not used. These versions of WebSphere Application Server Edge Components correct this problem.

  • If the portal serves only one markup, make sure the vary is set appropriately. If the portal serves multiple markups, set the vary appropriately and use a larger cache size. Use remoteCacheInfo.response.header.vary = space separated list of other http header fields to appropriately set the vary.

    Enter any HTTP header field names; use the HTTP 1.1 specification. The two most common http headers to specify here are vary = accept-language user-agent.

    The Vary value indicates the set of request-header fields that force a proxy to cache different variants of the same URL.

  • If the portal serves only one language, make sure the vary is set appropriately. If the portal serves multiple languages, set the vary appropriately and use a larger cache size. Use remoteCacheInfo.response.header.vary = accept-language to appropriately set the vary.

  • Only JSR portlets can override the cache lifetime setting at runtime.

With the above 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 as described in Setting configuration properties. 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 page, that user could read pages containing private information. By default, WebSphere Portal does not permit shared caching for authenticated pages. Use the Properties portlet or the XML configuration interface to override these default settings using the IgnoreAccessControlInCaches 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.

 

Troubleshoot

In general, you should monitor the cache hit rate on the proxy server and adjust the cache size appropriately. If the hit rate is lower than expected, increase the cache size. We can also check the following item:

  • Ensure that the cache settings for all portlets on the page are consistent with the cache settings for the page. For example, if one portlet on a page is set to only be cached in a private browser cache, then the entire page can only be cached in a private browser cache, and performance will not be optimal.

 

Related information

 

Parent topic:

Tuning