What database facebook is using to store clients information,contents etc. ?

Facebook is using various different technologies to manage its differennt functionality. Let us see them one by one.

1.  MySQL :  It is used to store user Information,  Wall Post, Timeline.

2.  MEMCACHED: It makes heavy use of MEMCACHED to reduce overhead from server and reduce reading time.

3.  HAYSTACK: It is used for every newly uploaded images. Facebook creates four copy of different size and generate unique id for each of them. The current growth rate of Photo Uploading in Facebook is220 million/Week.

4.  CASSANDRA: It is Apache Cassandra database used for high performance & Scalability. Facebook use it for Inbox Search. 

5.  SCRIBE: It is use for multitude of purposes internally. It is use to handling new logging Category

6. VARNISH: It is http accelerator which is use to serve photos and profile pictures, handling billions of request every day.

I hope this info would help you to meet what you were looking for. 

Kind Regards:

MD Danish

I read some where they are using Modified version of MySQl on some parts of there site but cant say exactly ,

DB size not matter that much this kind of projects use Split Tables on multiple server whith DB and Web Server cluster deploy seprately and heavly depands on programs like memcache to to seprate read request from write and use even that use reverse proxies to  reduce number of connection to DB server 

With that much resources in hand these are very small things