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Cache Policy Interaction—Maximum Age and Maximum Staleness

To help ensure that the freshest content is returned to the client application, the interaction of client cache policy and server revalidation requirements always results in the most conservative cache policy. All the examples in this topic illustrate the cache policy for a resource that is cached on January 1 and expires on January 4.

In the following examples, the maximum staleness value (maxStale) is used in conjunction with a maximum age (maxAge):

  • If the cache policy sets maxAge = 5 days and does not specify a maxStale value, according to the maxAge value, the content is usable until January 6. However, according to the server's revalidation requirements, the content expires on January 4. Because the content expiration date is more conservative (sooner), it takes precedence over the maxAge policy. Therefore, the content expires on January 4 and must be revalidated even though its maximum age has not been reached.

  • If the cache policy sets maxAge = 5 days and maxStale = 3 days, according to the maxAge value, the content is usable until January 6. According to the maxStale value, the content is usable until January 7. Therefore, the content gets revalidated on January 6.

  • If the cache policy sets maxAge = 5 days and maxStale = 1 day, according to the maxAge value, the content is usable until January 6. According to the maxStale value, the content is usable until January 5. Therefore, the content gets revalidated on January 5.

When the maximum age is less than the content expiration date, the more conservative caching behavior always prevails and the maximum staleness value has no effect. The following examples illustrate the effect of setting a maximum staleness (maxStale) value when the maximum age (maxAge) is reached before the content expires:

  • If the cache policy sets maxAge = 1 day and does not specify a value for maxStale value, the content is revalidated on January 2 even though it has not expired.

  • If the cache policy sets maxAge = 1 day and maxStale = 3 days, the content is revalidated on January 2 to enforce the more conservative policy setting.

  • If the cache policy sets maxAge = 1 day and maxStale = 1 day, the content is revalidated on January 2.

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