Function Introduction

Complete file origin fetching refers to CDN nodes fetching the complete file cache and responding to the client, regardless of whether the client request carries Range information or not. With complete file origin fetching enabled, CDN nodes can cache files for Range requests, thereby reducing the load on the origin server.

Note

Both complete file origin fetching and Range origin fetching achieve the effect of caching Range request content. If the origin server supports Range requests, it is recommended to prioritize configuring Range origin fetching to effectively improve file distribution efficiency, reduce initial packet delay, increase cache utilization, and reduce unnecessary origin fetching.

When enabling or disabling complete file origin fetching, the corresponding situations are as follows:

Disabling Complete File Origin Fetching

When the client initiates a Range request and the CDN node has no cache, it defaults to pass the client's Range request to the origin. Regardless of whether the origin server responds with a 206 or 200 status code, the CDN does not cache and passes the origin server's status code and content to the client.
When the client initiates a request for the complete file and the CDN node has no cache, it passes the client's request to the origin, the origin server responds with a 200 status code, the CDN caches the file, and responds with a 200 status code and content to the client.

Enabling Complete File Origin Fetching

When the client initiates a Range request and the CDN node has no cache, the CDN fetches the complete file in response to the complete file origin request. When the corresponding Range content is obtained, it begins to respond to the client with a 206 and the corresponding range data, while caching the complete file.
When the client initiates a request for the complete file and the CDN node has no cache, the CDN passes the client's request to the origin, the origin server responds with a 200 status code, the CDN caches the file, and responds with a 200 status code and content to the client.
When the client initiates a Range request and the CDN has cached the complete file, it directly responds with a 206 status code and corresponding range content to the client.

Complete file origin fetching is disabled by default, and the CDN fetches the origin based on the client's request method, whether with or without a Range request header.

Note

If the client has a Range request, the CDN cannot cache the corresponding file by default. You need to enable complete file origin fetching or Range origin fetching.

Applicable Scenarios

In general, when the origin server contains large files such as videos and apps, and the client may have Range requests, it is recommended to enable complete file origin fetching. This allows caching of files to fully utilize the CDN's capabilities.

Considerations

After this feature is enabled, if the client requests a Range towards the end of the file and the CDN node has a cache miss for the first visit, the client may need to wait for a long time to obtain the Range content, affecting the initial packet and first screen time. Additionally, if many clients only request part of the file and the origin server returns the complete file, it may result in wasteful origin traffic. For example, if a user requests Range: 5000-10000, and the complete file is 15MB, then the CDN fetches the complete file and starts responding with Range content at the 5000th byte, while caching the complete file. In this scenario, the user needs to wait for the origin's response time for bytes 0-5000; meanwhile, the origin responds with a 15MB file, but the user actually needs bytes 5000-10000, resulting in wasteful origin traffic.
If both Range origin fetching and complete file origin fetching are configured simultaneously, the former takes precedence.

Configuration Instructions

Complete file origin fetching is disabled by default, and this feature does not currently support self-service configuration by customers. If you need to use it, please contact our customer support team via hotline (852)31000000 or email global.noc@chinatelecomglobal.com for manual setup.

Content Delivery Network

Complete File Origin Fetching