When NetCache checks for canceled articles

What is a canceled article?

A canceled article is one that was posted to a news server but subsequently withdrawn by either the posting user or an administrator.

The posting user might cancel an article if, for example, the user made a mistake while creating the article. An administrator might cancel an article if, for example, the administrator is attempting to control abuses of the news service, such as advertisements posted to a newsgroup inappropriately.

About checking for canceled articles

NetCache uses the setting in the Canceled Article Time-To-Live option (Setup tab > NNTP > Caching Behavior) to determine when to check to determine whether an article has been canceled. The default is 3600 seconds (60 minutes). The Canceled Article Time-To-Live time period should be longer than the NNTP Refresh Rate (Setup tab > NNTP > General) time period.

When NetCache receives a request for an article, it first determines whether the article is in its cache. If the article is in the cache, NetCache then determines whether the article has been in the cache for a period equal to or greater than the Canceled Article Time-To-Live setting. If the article has been in the cache less than the Canceled Article Time-To-Live setting, NetCache serves the article to the client.

NetCache does not contact the news server (or other news cache) to find out about canceled articles until it receives a client request for an object whose Time-To-Live has expired.

If the article has been in the cache longer than the Canceled Article Time-To-Live setting, NetCache queries the host specified in the NNTP Server option to determine whether the article has been canceled. If the article has not been canceled, NetCache serves the article to the client from its cache. If the article has been canceled, NetCache sends a message to the client stating that the article has been canceled.

If this news cache points to another news cache, the Canceled Article Time-To-Live time period is the sum of the Canceled Article Time-To-Live time period that is set on this news cache and the Canceled Article Time-To-Live time period that is set on the other news cache.

How often NetCache should check for canceled articles

How often you want NetCache to check the news server for canceled articles depends on how consistent you want the NetCache information to be with the news server. The default Canceled Article Time-To-Live value is 60 minutes. This means that NetCache will request information about an article when it receives the first client request for the article after the article has been in the cache for 60 minutes.

For many organizations, the default value of 3600 seconds (60 minutes) provides a good balance between consistency with the news server and maximal hit rate and bandwidth savings. However, your organization might require a different setting in order to meet its goals.

Use the guidelines in the following table when changing the Canceled Article Time-To-Live setting.

If your organization's priority is...	Then do this...
High degree of consistency between the information that NetCache has and the information on the news server	Set the Canceled Article Time-To-Live option to a very low value.
High hit rate and bandwidth savings	Set the Canceled Article Time-To-Live option to a high value.