For invalidating

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For example, if you are using Oracle Web Cache Manager provides an easy-to-use interface for invalidating cached objects.

The advantage of using this interface is that the administrator is isolated from the intricacies of the HTTP and XML formats, and consequently, there is less chance for error.

As described in Section 6.7, you create expiration policies and associate them with caching rules to refresh content from the origin server.

Even with expiration policies, it is often difficult to predict when exactly content becomes stale.

This is a circumstance in which ESI inline invalidation does not work; Oracle Web Cache can only use ESI invalidation tags in conjunction with a response body that contains HTML.

With response header invalidation, origin servers can send invalidation directives in a proprietary invalidation response header.

Oracle Web Cache supports the following forms of invalidation: and provides a useful way for origin servers to "piggyback" invalidation messages on HTTP responses sent to Oracle Web Cache.

If fewer objects than the number specified meet the invalidation criteria, Oracle Web Cache lists only the URLs for those objects that meet the criteria.

When objects are marked as invalid and a client requests them, they are removed and then refreshed with new content from the origin servers.

You can choose to remove and refresh invalid objects immediately, or base the removal and refresh on the current load of the origin servers.

In addition to its greater flexibility in terms of response body content returned, response header invalidation requires less coding effort on the part of the Web applications since building an invalidation header is a fairly lightweight task.

Response header invalidation functions similarly to inline invalidation; origin servers "piggyback" invalidation directives on responses sent to Oracle Web Cache.

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