This topic describes the major performance indicators that are used to evaluate the performance of content delivery before and after a website is accelerated by Alibaba Cloud CDN.

Alibaba Cloud CDN can reduce loads on origin servers and accelerate content delivery. Performance indicators reflect the performance of content delivery before and after a website is accelerated by Alibaba Cloud CDN. You can use common and scenario-specific performance indicators to evaluate the content delivery performance. This helps you evaluate the performance of Alibaba Cloud CDN and make informed business decisions.

Common performance indicators

The following figures show some major performance indicators that can be used to evaluate the performance of content delivery before and after the website is accelerated by Alibaba Cloud CDN. The following table describes some common performance indicators of Alibaba Cloud CDN.
  • How content is delivered to a clientUpload content
  • How content is downloaded by a clientDownload content
Performance indicator Description
DNS time The time it takes for a client to initiate a request and to receive the IP address of the destination host.
TCP time The time it takes for a client to establish a TCP connection to the destination server.
SSL time The time it takes for a client to establish an SSL connection to a web server.
Delivery time The time it takes to complete sending a request after SSL shakes are completed.
Connection time If a CDN node uses HTTP to accelerate content delivery, the connection time consists of the DNS time and TCP time. If a CDN node uses HTTPS to accelerate content delivery, the connection time consists of the DNS time, TCP time, and SSL time. The connection time shows the number of available CDN nodes and their capabilities for content delivery.
Response time The time it takes for a web server to process an HTTP request and returns a response to a client.
Download time The time it takes for a client to receive and download the first packet returned from a web server.
Time to first packet The time it takes for a client to send a request and receive the first HTTP packet from a server. The time to first packet shows the overall performance of CDN nodes.
  • For content uploading, the time to first packet consists of the DNS time, TCP time, SSL time, request delivery time, and response time.
  • For content downloading, the time to first packet consists of the DNS time, TCP time, SSL time, request delivery time, and response time.
Note A newly purchased domain name may require a longer period of DNS resolution time than other domain names. This is irrelevant to the cache retrieval time.
Overall performance The time it takes to upload or download an entire file.
Packet loss rate The ratio of lost packets to total packets during transmission.
Back-to-origin rate The back-to-origin rate is classified into the back-to-origin request ratio and back-to-origin data transfer ratio.
  • Back-to-origin request ratio: the ratio of requests redirected to the origin server to total requests. Requests are redirected to the origin server when the requested content is not cached, has expired, or cannot be cached on edge nodes. The lower the ratio, the higher the performance.
  • Back-to-origin data transfer ratio: the ratio of the amount of data transfer from the origin server to the CDN node to the amount of outbound data transfer from the CDN node to the client. The following formula is used to calculate this ratio: Back-to-origin data transfer ratio = Amount of data transfer from the origin server to the CDN node/Amount of outbound data transfer from the CDN node to the client. The lower the ratio, the higher the performance.
Cache hit ratio The cache hit ratio of Alibaba Cloud CDN is classified into the byte cache hit ratio and request cache hit ratio. The cache hit ratio of Alibaba Cloud CDN is represented by the byte cache hit ratio. The higher the ratio, the higher the performance.
  • Byte cache hit ratio = Number of bytes returned for cache hits/Number of bytes returned for all requests
    Note A lower byte cache hit ratio indicates a higher amount of back-to-origin network traffic. A higher amount of outbound traffic from the origin server indicates a higher bandwidth value and more loads on the origin server. Therefore, back-to-origin network traffic represents the amount of loads on the origin server, and the byte cache hit ratio is the major concern in actual business scenarios.
  • Request cache hit ratio = Number of cache hits/Number of all requests
Note The back-to-origin rate and cache hit ratio described in the preceding table are used to evaluate the performance of content delivery for a website after it is accelerated by Alibaba Cloud CDN. If your website is not accelerated by Alibaba Cloud CDN, the back-to-origin rate is 100%, and the cache hit ratio is 0.

After a website is accelerated by Alibaba Cloud CDN, the network latency, packet loss rate, and back-to-origin rate are typically reduced, and the cache hit ratio is increased. However, the actual performance may vary based on the business scenario and workload type. The performance indicators described in this topic are based on pure statistics.

Alibaba Cloud CDN also provides scenario-specific indicators for you to evaluate performance in specific scenarios.

Performance indicators for small file distribution

Small files refer to HTML, JavaScript, JPG, and CSS files. The delivery of these types of file is latency-sensitive. The latency is determined by the connection time, time to first packet, and download time. Among these factors, the time to first packet is the core indicator. A website may lose its visits if it has a long page load time.

Alibaba Cloud CDN provides a configuration guide for accelerating the delivery of small files. For more information, see Image and small file distribution.

Performance indicators for large file distribution

Large files refer to files that are larger than 20 MB. The core indicators for large file distribution are the download rate and download time.

Alibaba Cloud CDN provides a configuration guide for accelerating the delivery of large files. For more information, see Large file distribution.

Performance indicators for on-demand video and audio streaming

On-demand audio and video streaming mainly uses FLV, MP4, WMV, and MKV files. The core indicators for on-demand video and audio streaming are the initial load time and stalling rate.
  • Initial load time

    The initial load time refers to the total amount of time that it takes to complete loading the first frame of a stream. The initial load time is determined by the DNS time, connection time, and time to first packet.

  • Stalling rate

    Stalling events may occur when a video or audio stream is played or a resource is loaded. The stalling rate refers to the rate of viewers that have stalling events among every 100 viewers. The lower the stalling rate, the higher the performance.

Alibaba Cloud CDN provides a configuration guide for accelerating on-demand video and audio streaming. For more information, see On-demand audio and video streaming.