Edge Security Acceleration:Refresh and prefetch resources

How purge and preferch work

Scenarios

Notes

• Notes on cache purge:

  • Submitting many purge tasks clears a significant amount of cache. This causes a sudden increase in back-to-origin bandwidth and requests, which increases the load on your origin server. We recommend that you perform this operation during off-peak hours.

  • A purge task takes about 5 to 6 minutes to take effect. If the cache time-to-live (TTL) for a file or directory is less than 5 minutes, you do not need to perform a purge. You can wait for the cache to expire and update automatically.

  • URL purge, directory purge, and regex-based purge all support shared cache. If a domain name is configured with a shared cache, you can submit a purge task using the primary domain name or any associated domain name to clear the cache.

• Notes on cache prefetch:

  • After a prefetch task is submitted and successfully executed, the DCDN nodes immediately retrieve the required resources from the origin server. Submitting many prefetch tasks at once generates many concurrent back-to-origin requests, which causes a sudden increase in back-to-origin bandwidth. We recommend that you perform this operation during off-peak hours.

  • By default, a prefetch request includes the Accept-Encoding:gzip header. If you need the prefetch request to include other headers or to implement multi-replica prefetching, you can call the Prefetch URLs API operation. Set the WithHeader request parameter to customize prefetch headers.

  • During prefetching, if the origin server returns a redirection status code, such as 307, the prefetch task does not follow the redirection to retrieve the resource. As a result, the prefetch task fails. However, if the origin server returns a 301 or 302 status code and you have enabled the 301/302 redirects for origin fetch feature in DCDN, the prefetch task is not affected.

• General notes:

  • If a domain name is configured with Rewrite Access URL, the DCDN node uses the rewritten URL to generate the CacheKey. Therefore, you must submit the rewritten URL for refresh and prefetch operations.

  • To use a Resource Access Management (RAM) user to refresh and prefetch resources, you must first grant the required permissions to the RAM user. For more information, see Grant permissions to a RAM user to refresh and prefetch resources.

  • You cannot abort a URL purge or cache prefetch task after it is submitted.

  • When you submit a cache purge or prefetch task, if the URI contains non-ASCII characters, such as spaces or Chinese characters, you must encode the URL. Otherwise, the content management system cannot recognize the task. Ensure that the submitted URI is in the encoded format.

Refresh resources

1. Log on to the DCDN console.

2. In the navigation pane on the left, choose Management Tools > Purge and Prefetch.

3. On the Purge Cache tab, configure the refresh rules.

   

   Parameter	Description
   Operation	Select Purge.
   Operation Method	You can refresh by URL, Directory, or Regular Expression.
   URL	By default, an Alibaba Cloud account can submit a maximum of 10,000 URL refresh tasks and 100 directory refresh tasks per day. A directory refresh task includes subdirectories. If the peak bandwidth of your Alibaba Cloud account is greater than 200 Mbps, you can apply for a quota increase in Quota Management. Alibaba Cloud evaluates your request as needed. By default, an Alibaba Cloud account can submit a maximum of 20 regex-based refresh tasks per day. If the peak bandwidth of your Alibaba Cloud account is greater than 10 Gbps, you can submit a ticket to apply for a quota increase. URL refresh The URL must start with http:// or https://. To refresh multiple URLs, enter one URL per line. Directory refresh The URL must start with http:// or https:// and end with a forward slash (/). To refresh all files in the root directory: http://example.com/. To refresh all files in the /path/test/ subdirectory: http://example.com/path/test/. To refresh multiple URLs, enter one URL per line. You can submit a maximum of 100 directory refresh tasks at a time. You can submit a maximum of 100 directory refresh tasks per minute for a single domain name. By default, directory refresh uses the "refresh changed resources" method. If a user request matches a resource in the directory, the DCDN POP retrieves the Last-Modified information of the resource from the origin server. If the information is the same as that of the currently cached resource, the POP directly returns the cached resource. If it is different, the POP pulls the new resource from the origin server, returns it to the user, and caches the new resource. Regex-based refresh For more information, see Regex-based refresh.

4. Click Submit.

5. View the refresh progress.

   After you submit a refresh task, you can view the details and progress of the task on the Records tab. The task may take a long time to complete if you refresh many resources.

   Note

   If you enable DCDN Cache Auto-Refresh in the OSS console, you cannot view the auto-refresh tasks that are triggered by OSS in the DCDN console.

Prefetch resources

1. Log on to the DCDN console.

2. In the navigation pane on the left, choose Management Tools > Purge and Prefetch.

3. On the Purge Cache tab, configure the prefetch rules.

   

   Parameter	Description
   Operation	Select Prefetch.
   Operation Method	Only URL prefetch is supported.
   URL	The URL must start with http:// or https://. The prefetch URL must be the exact path of a resource file. Directories ending with a forward slash (/) are not supported. To prefetch multiple URLs, enter one URL per line. URL prefetch quota (daily): An Alibaba Cloud account can submit a maximum of 1,000 URL prefetch tasks per day. You can submit a maximum of 100 URL prefetch tasks at a time. If the peak bandwidth of your account is greater than 500 Mbps, you can see Quota Management to apply for a quota increase. Alibaba Cloud evaluates your request as needed. Prefetch queue rule: The prefetch queue for each account can hold a maximum of 100,000 URLs. DCDN prefetches URLs in the order they are submitted. When the number of URLs to be prefetched in the queue reaches 100,000, DCDN rejects new prefetch tasks. Prefetch speed: The execution speed of a prefetch task is related to the average size of the files to be prefetched. The smaller the average file size, the faster the prefetch speed.

4. Click Submit.

5. View the prefetch progress.

   After you submit a prefetch task, you can view the details and progress of the task on the Records tab. The task may take a long time to complete if you prefetch many resources.

Related API operations