Relational Databases

An experience by a young startup aficionado

"The primary online data store for an application is the worst place to take a risk with new technology."  

Adam D' Angelo

(Quora CEO)

CAP Theorem

"Of three properties of shared-data systems-data Consistency, system Availability and tolerance to network Partitions - only two can be achieved at any given moment in time."

2000 Prof. Eric Brewer, PoDC Conference Keynote

2002 Seth Gilbert and Nancy Lynch, ACM SIGACT News 33(2)

How do I choose the right database?

It's all about Trade-offs 


But is it really just about the trade-offs?

Trade-offs and theories are confusing!!!

Allow me to share some

Hands-on experience...

Kuai List Headquarters: The most improvised white-board ever!

Requirement #1:

What do we know already?

Requirement #2:

What is trending?


That was easy!!!

Requirement #3:

What about Complex Queries?

AHA!!! Relationships do matter right?

Requirement #4:

What about Transactions?

  • It ensures that you atomically make changes to your database.

Requirement #5:

What about Consistency?

  • It ensures that clients have the same view of the data
  • Achieved through ACID transactions

Requirement #6:

How about Scaling?

  • Option 1: I assume we can scale as we go
  • Option 2: How about implementing Layers (Memecaches) on top of Relational DBs. (Facebook, Twitter and Airbnb)



  • Option 3: If scaling is urgent, how about partitioning at the application level. (FriendFeed)

Use Case: Kuai List

  • We use PostgreSQL for writing and updating listings.
  • For retrieving in desirable speeds we use memecache on top of our core relational database.
  • How about data that never changes?

Challenge #1: Host in the Cloud

  • Our host (Heroku) offered limited records (10,000 rows).
  • We migrated to Amazon RDS: with zero downtime
    • Amazon RDS makes it easy to use replication to enhance availability and reliability for production workloads

Synchronous replication

Data-center B

Data-center C

Data-center A

Data-center D


If scaling is needed, How about partitioning at the application level.

Layers are very important (MemedCached server and Amazon S3). they can sit on top of a MYSQL database (only in charge of writes)


How far can I go with using Relational Databases like MySQL and PostgreSQL


How far can I go with using Relational Databases like MySQL and PostgreSQL?




By Omar Sar

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