Design Lesson 1

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Design

• Database Design

• System Design

• Object Oriented Design

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What is design?

give a higher level architecture and design an entire system rather than some individual components

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What can we tell?

• an entire system
• a higher level architecture
• some individual components

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What should we do?

• Ask about details that you care 
• Give yourself one minute, do not hurry
• Begin with the blueprint (whole architecture)
• fulfill each individual part but not minor details

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What are the most important things for a system?

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Accuracy?

Should we pursue 100% accuracy?

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Example: 

Billing Information,

Bank Transaction,

Google Search Results

Performance?

Could we let users wait too long to get what they want?

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Trade off: Accuracy

Robustness?

How to deal with edge case?

How to deal with attacks and scrapers?

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Accuracy

• Database Read and Write: race condition
• Throw Exception at proper time: good exception supress
• Conditional check: prevent NPE

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Performace

• What database? Cache layer?
• Scalability & Distributed System
• Site speed: TTFB, Async call, make effort alap

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make effort as little as possible? Generic

Robustness

• Scalability & High QPS
• Backup System
• Network Security

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Knowledge pieces

• Database
• Network,Server,TCP/IP
• Security, Encryption/Decryption
• Distributed System
• Backup System
• *Hadoop

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Design pieces

• Accuracy
• Performance
• Robustness
• Scalability
• Test

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Google Calendar

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Google Calendar

Design a simple google calendar. It has following requests:

1. The user could register himself using email address

2. The user could have some personal profiles

3. The user can be an organizer and create events and add some detail information for the event

4. The user could add/remove some users to/from his events and send invitation via email

5. The user could know if the people they add is busy or free during the time he sets up for the event.

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Follow up questions

• How to tell if someone is busy or not during this time of the event?
• How to deal with so many emails sending? And what if some of them fails?
• How to evaluate the performance? How to improve it?

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