Macro Process: when play a music on a web page

Remote request - Local prepare - Remote reply - Local process

  • Step 0, Browser prepare
  • DNS
    • Step 1, Browser Send DNS request
    • Step 2, Prepare DNS reply
    • Step 3, Send DNS reply
    • Step 4, Browser Process DNS reply
  • Web Server
    • Step 5, Browser Send webpage request
    • Step 6, Prepare webpage reply
    • Step 7, Send webpage reply
    • Step 8, Browser Process webpage
  • Music player
    • Step 9, Browser Request music player
    • Step 10, Prepare music palyer
    • Step 11, Send music player
    • Step 12, Browser process music player
  • File Server
    • Step 13, Browser request MP3 file
    • Step 14, Prepare MP3 file
    • Step 15, Send MP3 file
    • Step 16, Browser Play MP3 file

How to Collect failure log

  • when user access webpage, server log it
  • when user can play music, user send a log to server
    • without user send, server cannot determine whether music is successfully palyed

Failure sub problems: music cannot be played

  • Local Client can bypass DNS Server part

  • DNS Server part

    • Step1, Check local Hosts file
      • HOSTS hijack, someone modify hosts file, point website to somewhere
      • Solution: hosts file analysis by our software
    • Step2, DNS server analysis by ISP (Internaet Service Provider)
      • some ISP fails to update the latest DNS after changing server address
      • Solution: talk to ISP
    • Check itself or ask others (poison form others)
    • Send IP address back (hijacked by middleman)
    • Blocked by some companies' networking

  • Web Server part

    • Peak time: reverse proxy with more servers, nigix

      • do the similar job to load balancer

      • receptionist, dispatch request, reduce thread change,

      • More than load balancer: cache, group request

    • Reduce the size of webpage: simplify content, compress/merge images, lazy load

    • More cacheable pages: change dynamic webpage into static webpage

      • server side caching

      • client side caching

    • User may just close....webpage, failure cannot rule out

  • Music Player

    • Step 13, network error: repair / remove failure server.

    • Step 14, failing to find MP3 file: URL may expired. Server need sync clock routinely

    • Step 15, connection timeout: Optimize CDN(COntent Delivery Network), Compress MP3 with lower bitrate, Pre-loading

    • Step 16, play MP3 failure: maybe a bug in audio transcoding, re-transcoding the bad files

    • Other: user just close, versions of flash platers, iOS device may not support, develop HTML5 player

Validate Improvement

  • daily active users? No, it depends on too many factors
  • one day retention rate? Yes, how many user re-enter or come back to the webpage. more is valuable.

Rate Limit - limit Query Per Second

  • algorithm of gap: limit the gap between two request

    • bad case: maybe overhead. Change to time-bucket, 1second 1bucket
    • Time Example: 1.1, 1.5, 1.6, 1.7, 1.8, 1.9 -> 6 request in 1s

  • How to limit requests in every one second?

    • Save space without Database: reuse one time-bucket. When found current time != previous time, clean current bucket
    • Database? : use 1 second as the key. when new comes, check current 1 second

  • How to limit requests in any one second? 1.2, 1.3, 1.5, 1.7, 1.9, 2.1 -> 6 request in 0.9s

    • use requestList, every request will check previous 5th time, >1s OK, <1s drop
    • reuse requestList

Follow up

  • How to save space with 10^9 query per hour?
    • Counter: simple one
    • Batch queries: group request, 10^3 request one group
  • How to support multiple threads?
    • lock
  • How to limiter on users?
    • <uid, requestList>
  • How to support query with different quotas?
    • acquire(quota) -> Token Bucket

Algorithm of Token Bucket - Space complexity O(1)

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