How does twitter work?

How do hashtags work on Facebook and Twitter ?

• Hashtags are awesome. But I want to know that how they work on Facebook and Twitter ? In what priority do we get the results ? How do hashtags search ? What are the privacy settings used ?

• Answer:

  Hash tag working internalsHashtags is a cool feature of twitter and recently introduced in Facebook.   It can be considered as a mechanism to view all those posts/ tweets which share common hashtag. A post/tweet can contain more than one hash tag. Before we go into details as how the hash tags work lets get a simple idea of how the tweets/posts are represented in these Web services (Twitter/Facebook) For eg I make a post in Facebook with say a hash tag #IPL   "Indian cricket is doing well because of #IPL"   (say user id = 1001, post id = 2001)   Now the post is represented as <user-id> - <post-id> -<hash-tags> 1001 - 2001 - #IPL So now it simplifies to retrieving all the posts with post-id that is part of a given hash-tag list. So the key happens to be the hash tag while the posts which contains the particular hash tag is the value that corresponds to a hash tag <hash tag> - <list of posts with that hash tag> #IPL - Append 2001 to list To understand the big picture of the working of such hash tag search in Facebook like web services see the following conceptual architecture. There is a distributed cache layer which is the real performance booster for these services. The distributed cache is responsible of keeping track of the recent activities in the in-memory database rather than performing slow data base access. By in-memory database it refers to main memory database (MMDB) which is much faster as it relies on the RAM for the data storage (cache).     Not to mention the actual architecture is lot more complicated, the figure shows only abstract layers. Facebook uses a distributed cache service called Memcache in the distributed cache layer. This distributed cache is a hot. Microsoft, Facebook, Amazon all have their own framework of distributed cache supporting their cloud services. Microsoft has a distributed cache called Velocity which is bonded to many services such as Azure and other cloud services.