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.

You can make informed business decisions based on the performance indicators. Performance indicators include:

Common performance indicators

You can monitor the following performance indicators to evaluate the performance of content delivery before and after your website is accelerated by Alibaba Cloud CDN. Common performance indicators include but are not limited to the ones described in this topic.
Note
  • 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.
  • The back-to-origin rate and cache hit ratio described in the following 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.
  • How content is delivered to a clientHow content is delivered to a client
  • How content is downloaded by a clientHow content is downloaded by a client
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 handshakes are completed.
Connection time If a CDN edge node uses HTTP to accelerate content delivery, the connection time consists of the DNS time and TCP time. If a CDN edge 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 edge nodes and their capabilities for content delivery.
Response time The time it takes for a web server to process an HTTP request and return 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.
  • The back-to-origin request ratio refers to the ratio of requests to resources that are not cached, have expired, and cannot be cached on CDN edge nodes to total requests. Back-to-origin request ratio = Number of back-to-origin requests from CDN edge nodes/Total number of requests sent to CDN edge nodes. A lower back-to-origin request ratio indicates a higher performance. However, if the original user requests are fragmented after CDN edge nodes redirect them to the origin servers, the number of back-to-origin requests becomes greater than the total number of requests sent to CDN edge nodes.
  • The back-to-origin data transfer ratio refers to the ratio of data transfer returned by the origin servers to data transfer returned by CDN edge nodes to clients. Back-to-origin data transfer ratio = Number of bytes returned from the origin servers to CDN edge nodes/Number of bytes returned from CDN edge nodes to clients. A lower data transfer ratio indicates a higher 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 = (Total number of bytes returned from CDN edge nodes to clients - Total number of bytes returned from the origin servers to CDN edge nodes)/Total number of bytes returned from CDN edge nodes to clients.
    Note A lower byte cache hit ratio indicates a higher amount of back-to-origin traffic. A higher amount of outbound traffic from the origin server indicates a larger bandwidth value and heavier workloads of the origin server. Therefore, back-to-origin traffic represents the amount of workloads on the origin server, and the byte cache hit ratio is the major concern in actual business scenarios.
  • Request cache hit ratio = (Total number of requests to CDN edge nodes - Total number of back-to-origin requests)/Total number of requests to CDN edge nodes.

Performance indicators for small file distribution

Small files refer to HTML, JavaScript (JS), JPG, and CSS files. The delivery of these types of file is latency-sensitive. The lower the latency, the higher the performance. The latency is determined by the following factors:

  • Time to first packet (most critical factor)
  • Connection time
  • Download 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 key indicators for large file distribution include:
  • Download rate
  • 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 key indicators for on-demand video and audio streaming include
  • 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. The shorter the initial load time, the higher the performance.

  • 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.