Revalidating HTTP objects

Web Proxy Caching > Ensuring cached object freshness > HTTP object freshness > Revalidating HTTP objects

When a client requests an HTTP object that is stale in the cache, Content Gateway revalidates the object, querying the origin server to check if the object is unchanged. Revalidation results in one of the following:

If the object is still fresh, the proxy resets its freshness limit and serves the object.

If a new copy of the object is available, the proxy caches the new object, replacing the stale copy, and serves the object to the user simultaneously.

If the object no longer exists on the origin server, the proxy does not serve the cached copy.

If the origin server does not respond to the revalidation query, the proxy does not perform any validation; it serves the stale object from the cache.

By default, the proxy revalidates a requested HTTP object in the cache if it considers the object to be stale. The proxy evaluates object freshness as described in HTTP object freshness. You can configure how often you want the proxy to revalidate an HTTP object.

1.	Navigate to the Configure > Protocols > HTTP > Cacheability tab.

2.	In the When to Revalidate area of the Behavior section, select:

Never Revalidate to never verify the freshness of a requested HTTP object with the origin server.

Always Revalidate to always verify the freshness of a requested HTTP object with the origin server.

Revalidate if Heuristic Expiration to verify the freshness of a requested HTTP object with the origin server if the object contains no Expires or Cache-Control headers. Content Gateway considers all HTTP objects without Expires or Cache-Control headers to be stale.

Use Cache Directive or Heuristic to verify the freshness of a requested HTTP object with the origin server when Content Gateway considers the object in the cache to be stale. This is the default.