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Excerpt
This topic describes how to configure caching in XperienCentral which is essential for websites that experience high traffic.
It eanbles the website to handle the load created by many page requests by using an intelligent mechanism that returns pages without having to regenerate them completely. The XperienCentral caching module is also tailored to not nterfere with visitor interaction and personalization.

In This Section

Table of Contents
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Architecture and Overview

Caching occurs in the front-end server processes and has links with JSP rendering [D] and the time stamps table [E], as you can see in the image below. A page request [A] from a website visitor goes through some filters [B] and arrives at the caching module [C].

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  1. [A] Retrieve the timestamp of the page (or SSI) by performing a query on the Timestamp database. The database is not always queried but instead the timestamps are also cached in the caching module. The timestamp is compared with the date of the file in the cache. If the timestamp is newer then the file is returned [D], otherwise the page has to be rendered.
  2. [B] The page must be regenerated. Therefore a request goes from the caching module to the backend servlet to render the page. This takes some time and it’s the slowest scenario. After the page has been rendered it is stored as a file in the cache directory [C] and the page is returned.

 

 

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Pages and Server Side Includes

In a very basic setting the caching module can save local cache files based on every page request, for example every URL. But in several cases this may not really speed up the page because parts of the page might change often. Dynamic Content Overviews are an example of page sections that can change often.

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This SSI tag will render a Content Overview element with the ID 68647. There are more parameters that describe the element’s context, for example a. Page ID, Content Item ID, web initiative ID, and so forth.

An SSI Example: the Poll Element

Polls are elements that can change quite often when a lot of people vote. Therefore it is better to use an SSI for the Poll Element. In a basic situation where you add a poll element to a page, the page.jsp is used as a starting point. The page.jsp will require the /pagepart/content.jspf, which will call the /element/pollElement.jspf. Before we look into this .jspf let’s examine the /element/pollElement.xml file:

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  1. First make sure you can login to your application server as an administrator. For Tomcat this involves editing the file /conf/tomcat-users.xml in the Tomcat directory. Example:

    Code Block
    themeEclipse
    <?xml version='1.0' encoding='utf-8'?>
<tomcat-users>
<role rolename="wmadmin"/>
<user username="wmadmin" password="123456" roles="wmadmin"/>
</tomcat-users>



  2. Restart Tomcat and go to the URL http://<hostname>:<port>/web/admin. Enter the username and password.
  3. Create a page in XperienCentral and add a Poll element. Enter some information in the poll element and publish the page.
  4. Open the page on the backend hostname: open a new tab/window in your browser and go to  http://<hostname>:<port>/web/show. This will show the homepage of your website without using the cache. Navigate to the page with the poll element.

  5. Add the following string to the URL of the page: /ssidebug=true and refresh the page. This should show the string we have seen in the previous paragraph, something like:


    Code Block
    themeEclipse
    <!--#include virtual="/web/show?id=26111&langid=43&cachetimeout=120&elementHolder=26114&ssiObjectClassName=nl.gx.webmanager.cms.element.PollElement&ssiObjectId=72418"-->


    It’s possible to paste the marked part after your backend hostname and port number and open it in a browser. You will then see the code of the poll element and nothing else. This exercise shows that individual SSIs can be rendered on their own by passing the right parameters (such as elementHolder and ssiObjectClassName to a /web/show command.

 

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Working with the Caching Module

Enabling Caching

  1. To enable caching go to /wiki/spaces/PD/pages/24721486  section of the General tab of Setup Tool - ensure that the allow_cache checkbox is selected.
  2. You can test if it works by requesting several pages on the front-end. Verify if there are subdirectories with numbers created in the cache directory (the default is /work/cache for local installations and /cache for production servers).
  3. If you want to make sure that most pages are generated (and therefore in the cache) before a website goes live you can run the XperienCentral search engine. 

 

Cache Configuration Settings

You can find most of the caching settings in the /wiki/spaces/PD/pages/24721486  section of the General tab of Setup Tool. The relevant cache options are:

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ParameterDescription

allow_cache

Enables/disables caching in the XperienCentral frontend.

application_filter_definition_url_base

Specifies the URL where the configuration for external application integration is located.

cache_cacheable_response_codes

A comma-separated list of cacheable response codes. The default is "200" (successful response from the server). Only codes that denote an immediate successful response should be entered.

cache_directory

The folder where the files containing cached content is stored.

cache_directory_depth

The maximum depth that the folder tree used for caching can reach. The recommended value is 3.

cache_max_stale_time

The number of seconds that the frontend will serve an old version of a page from the cache while the page is being regenerated by the backend. The recommended value is 0.

cache_number_of_directories

The maximum number of subfolders that will be created for the caching directory structure. The recommended value is 30.

cache_statement_timeout

Specifies the number of seconds between queries from the frontend to ensure the validity of cached content.

cache_timestamp_expire

The maximum number of seconds that a query to the Timestamp database is allowed to take. If there is no response from the database within this time period, the cached version of the page is returned. The recommended value is 2.

 

Caching Optimization in the Edit Environment

Some caching optimization can also be done in the edit environment of XperienCentral. Every page section can have a caching timeout value. This will prevent the rendering of the page section more than once in the time span specified by the caching timeout. Common page sections that can benefit from a caching timeout value are page sections that contain navigation such as menus.

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On the other hand be careful with very dynamic page sections. If you set a caching timeout for these types of page sections you might frustrate site editors because it takes too long for new content or content changes to show up.

Clearing the Cache

In a normal situation XperienCentral takes care of the required actions to clear the cache when content is changed, added or removed. When an editor adds an element to a page the timestamp for the page will be set to the current date and time. The caching mechanism will notice this when the page is requested and the page will be regenerated.

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When you launch a new website you can initialize the caching module by clicking on the [Update timestamps] button next to the "Initialize caching" label. This will create a timestamp entry for each page.

Timestamps in the Database

For debugging purposes it might be necessary to look at the timestamps more closely. Timestamps are stored in the XperienCentral external database in the following seven tables:

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TableDescription

Tsdatabaseentitytimestamp

 

Used for database detail pages. Timestamps are identified by the "dbid" parameter.

Tsdatabasetimestamp

 

Used for all databases. Timestamps are identified by the database ID.

Tsdiscussiontimestamp

 

Used for discussion timestamps. Timetamps are identified by the thread ID.

Tsjellycontenttimestamp

 

Used for Content Repository items. Timestamps are identified by media repository content ID.

Tsjellyfishtimestamp

 

Used for an Content Repository of a web initiative. Timestamps are identified by web initiative ID.

Tsobjecttimestamp

 

Used for various XperienCentral objects such as pages and page sections. Timestamps are identified by object ID. For pages this is also the ID in the URL of a page, for example
/web/show/id=26111 - 26111 is the object ID for this page.

tstermtimestamp

Used for Content Repository terms. When terms are changed they could influence content overviews so they have their own table. Timestamps are identified by term ID.

 

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Performance Checklist

The following checklist can be used to check the performance variables of a XperienCentral website. Performance involves more than XperienCentral and the caching module so other relevant settings are also taken into account.

Infrastructure

Application Server

  • Application Server (Tomcat or other) has sufficient memory.
    Recommendation: make sure the application server meets the system requirements for your version of XperienCentral and that the required amount of memory is available for the application server process.

  • The number of other applications (such as other application servers) is as low as possible
    Recommendation: for optimal performance run only one application server per server
    How to check: use a process list in UNIX/Windows and/or the netstat command to scan port usage

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    1. Pages with a high duration. Solution: investigate the page.
    2. A large number of requests from one IP address. Solution: block the IP address.
    3. Crawlers/search engines/robots (see the user agent string). Solution: add a robots.txt file or block the IP address.

Database Server

  • Make sure the transaction speed is fast enough
    Recommendation:  Websites with many database interactions can suffer severely from slow database servers and/or connections. Normal XperienCentral queries should take no longer than 1-2 seconds (maximum) with an average of tenths (1/10) of seconds. Queries to non-XperienCentral content should also be optimized.
    How to check:
    1. Monitor the log of the application server for database/query timeouts or JDBC errors
    2. Use the database manager in XperienCentral to run some test queries, for example:
    3. Use a database analysis tool to monitor the database speed and connection. This is beyond the scope of this document.

Application

Configuration

  • Make sure caching is enabled

  • Make sure there are no backend server names and server aliases listed under the frontend server names and server aliases
    How to check: Check the properties frontend_server_alias and frontend_hostname in the Setup Tool. These should not contain backend hostnames.
  • Consider using dumped static pages.
    Recommendation: When the normal caching mechanism fails or when one or more pages are for the larger part static you might consider dumping certain pages, such as the homepage.
    How to check: This can be set up in Configuration > Server configuration > [Dumped Content].

JSPs/programming

  • Make sure the URLs contain as little query string parameters as possible
    Recommendation: try to avoid using query string parameters to pass parameters to other pages or page sections. This will create more unique URLs and thus more pages have to be generated and not cached
    How to check: use http://<hostname>/web/admin/status to watch all incoming page requests.

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  • Avoid using hardcoded queries in JSPs
    Recommendation: hardcoded queries in JSPs don’t profit from the caching/timestamp mechanism and should therefore be avoided. Instead, use the XperienCentral query element or database pages.             

 

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FAQ

Q: Where can I find the cache directory?

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A: No timestamps will be found for any object or page so the cached file will be returned automatically. This happens until a requested object is changed and saved again.

 

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