This week’s system design refresher:

• CAP Theorem (Youtube video)

• How Git works

• Redis use cases

• Linux commands

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What is the CAP theorem? How useful is it to system design?

How does Git Work?

The diagram below shows the Git workflow.

Git is a distributed version control system. Every developer maintains a local copy of the main repository and edits and commits to the local copy. The commit is very fast because the operation doesn’t interact with the remote repository. If the remote repository crashes, the files can be recovered from the local repositories.

How can Redis be used?

There is more to Redis than just caching.
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Redis can be used in a variety of scenarios as shown in the diagram.

• Session
  We can use Redis to share user session data among different services.

• Cache
  We can use Redis to cache objects or pages, especially for hotspot data.

• Distributed lock
  We can use a Redis string to acquire locks among distributed services.

• Counter
  We can count how many likes or how many reads for articles.

• Rate limiter
  We can apply a rate limiter for certain user IPs.

• Global ID generator
  We can use Redis Int for global ID.

• Shopping cart
  We can use Redis Hash to represent key-value pairs in a shopping cart.

• Calculate user retention
  We can use Bitmap to represent the user login daily and calculate user retention.

• Message queue
  We can use List for a message queue.

• Ranking
  We can use ZSet to sort the articles.

Linux commands illustrated on one page!

Take a look at how many you know here :)

• Controlling processes: kill, killall, nice

• Scheduling jobs: sleep, watch, crontab

• Host location: host, whois, ping, traceroute

• Network connections: ssh, telnet, scp, ftp

• Screen output: echo, printf, seq, clear

• Viewing Processes: ps, uptime, top, free

• And many more

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