Writing a Cache Provider

In this short article we are going to learn how to write a simple Cache Provider for ScrewTurn Wiki 3.0 (STW from now on). A Cache Provider is a type of plugin that handles data caching for the purpose of improving performance.

Introduction to Cache Providers¶

This brief section assumes you have already a general knowledge on STW providers.

The main tasks a Cache Provider performs are:

• caching page data, both "backend" data (i.e. PageInfo and PageContent instances) and formatted page content (up to Phase2)
• caching "meta" data, such as the header, footer, etc., up to Phase2
• handling runtime data such as the number of users that are online, what pages are being edited at a given time and page redirections.
  

Caching of Page Data¶

The following methods are called by the wiki application for managing page data caching:

• SetPageContent sets the content of a page (instance of PageContent)
• GetPageContent gets the content of a page (instance of PageContent), if any
• SetFormattedPageContent sets the Phase2-formatted content of a page (string)
• GetFormattedPageContent gets the Phase2-formatted content of a page (string), if any
• RemovePage removes a page from the page cache
• ClearPageContentCache empties the entire page cache
• CutCache removes the specified number of least-recently used page items (both PageContent and formatted content) from the cache
• PageCacheUsage (property) returns the number of pages in the page cache (PageContent)
• FormattedPageCacheUsage (property) returns the number of formatted pages in the cache (formatted content).
  

Caching of Meta Data¶

The following methods are used by the wiki application for managing "meta" data caching:

• GetMetaDataItem gets a meta data item (string) from the cache, if any
• SetMetaDataItem sets a meta data item (string) in the cache (remove the item if the value is null)
• ClearPseudoCache empties the meta data item cache.
  

Management of Runtime Data¶

The following methods are called by the wiki application for managing runtime data:

• OnlineUsers (property) gets or sets the number of users that are online
  

• RenewEditingSession is called when a page editing session for a page, user has been started renewed (this information is used to handle concurrent page editing - sessions have a timeout that should be handled by the provider and whose value is specified by the EditingSessionTimeout system configuration setting)
• CancelEditingSession is called when a page editing session for a page, user has been completed
• IsPageBeingEdited tells the wiki if a page is being currently edited
• WhosEditing tells the wiki who is editing a page
  

• AddRedirection sets the source, destination of a redirection path (used for handling page redirections)
• GetRedirectionDestination gets the destination of a redirection, if any
• RemovePageFromRedirections removes a page from the redirections data, both from sources and destinations
• ClearRedirections empties the redirections data.