When NetCache checks for new articles

About checking for new articles

NetCache uses the cached group information to determine when to check the news server for new articles in a newsgroup.

When NetCache receives a request for a newsgroup, it first determines whether it has any information about the newsgroup. If NetCache has recent information about the newsgroup, NetCache provides that information to the client. Then, when the client requests an article in the newsgroup, NetCache provides the article from its cache or, if the object is not in the cache, retrieves the article from the news server.

However, if NetCache does not have recent information about the newsgroup, NetCache queries the news server to obtain this information. The frequency with which NetCache queries the news server for recent information about a newsgroup is set in the NNTP Refresh Rate option in the Appliance Manager (Setup tab > NNTP > Caching Behavior).

When NetCache checks for new articles

NetCache checks for new articles on the news server only when the following conditions are met:

NetCache has had newsgroup information in its cache for a time period equal to or greater than the NNTP Refresh Rate setting (the default setting is 10 minutes).
A NetCache client requests information about that newsgroup.

NetCache does not proactively check the news server for every newsgroup to determine whether new articles have been posted. Rather, NetCache waits until a client requests the newsgroup, then determines whether it has current information about that newsgroup. If it has current information about the news group, NetCache serves the information to the client. If it does not have current information about the news group, NetCache queries the news server for the information, caches a copy of the reply, and sends the information to the client.

How often NetCache should check for new articles

How often you want NetCache to check the news server for new articles depends on how consistent you want the NetCache information to be with the news server. The default NNTP Refresh Rate value is 10 minutes. This means that NetCache will request information about new articles posted to the news server when it receives the first client request for information about that newsgroup after the 10-minute time period has expired.

For many organizations, the default value of 10 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 NNTP Refresh Rate 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 NNTP Refresh Rate option to a very low value.
High hit rate and bandwidth savings	Set the NNTP Refresh Rate option to a high value.

The NNTP Refresh Rate option also directly impacts how NetCache updates the newsgroup list obtained from the NNTP LIST command. The list of newsgroups NetCache receives from the news server is a cacheable object. NetCache requests a new list of newsgroups if its object's cached time has exceeded the value specified in the NNTP Refresh Rate option. This also means that users will see whether new newsgroups have been created or old newsgroups deleted no later than the setting in the NNTP Refresh Rate option.