Design and Implementation of High‑Performance Scheduling, CDN, and IP Database Systems

The article introduces a network‑based scheduling system that routes user requests to backend servers based on rules, providing load balancing, fault isolation, health checks, logging, and permission management, making high availability and throughput essential as it becomes a single point of failure.

It describes a video playback system that uses standard HTTP to stream MP4 videos, which can be played directly in most browsers and smartphones.

CDN (Content Delivery Network) is explained as a layer of intelligent virtual nodes that redirect user requests to the nearest server based on traffic, load, distance, and response time, improving speed and stability of content delivery.

DNS (Domain Name System) is covered as a distributed database that maps domain names to IP addresses, enabling users to access services without remembering numeric IPs.

The concept of a CDN‑based video playback system is presented, highlighting how different DNS resolutions can direct users to nearby nodes for better experience, while noting issues such as misconfiguration and lack of centralized control for removing undesirable content.

Shortcomings of commercial CDNs are listed: reliance on DNS which depends on user settings, cost‑driven placement of nodes that can cause quality fluctuations during peak times, and inability to know node capacity, leading to overload.

IP‑based scheduling problems are discussed, including inaccurate IP‑to‑region mapping and cross‑operator IP allocation that can mislead routing decisions.

The article proposes a high‑performance scheduling system that obtains the real user IP, aggregates IP statistics to assess node proximity, load, and legality, and then routes requests to appropriate CDN points to improve user experience.

Current IP database issues are outlined, emphasizing the need for frequent updates due to constantly changing IP allocations.

The "Pure IP" library (QQWry.dat) is introduced, describing its file structure: an 8‑byte header, a record area with variable‑length entries, and an index area, along with redirection modes (1 and 2) used to reuse country and region strings.

Detailed diagrams illustrate the file header, record formats, redirection mechanisms, and index entries, explaining how binary search can quickly locate IP ranges.

Third‑party IP lookup services (e.g., Taobao, Sina, Sohu, IP138, IP.cn, IPIP) are listed, noting their limitations for commercial use.

Implementation ideas are presented: representing each C‑segment (256 IPs) with a 2‑byte IPC code that encodes country/region, province, city, district, and carrier information, enabling constant‑time lookup and simple XOR‑based distance calculations.

Methods for evaluating and recording video playback quality are suggested, including reporting at playback completion and aggregating data using the IPC code to detect and correct issues in real time.

Finally, the article argues that using IPC codes mitigates errors caused by inaccurate IP databases, as aggregation occurs only within the same C‑segment, preventing cross‑segment contamination.