Request flows

sequenceDiagram

title User Login

autonumber

Client->>LoadBalancer: LoginRequest

LoadBalancer->>UserApi: LoginRequest

UserApi->>UserService: LoginRequest

UserService->>UserCache: Lookup user

UserService->>UserDB: If not found from cache, lookup from DB

UserService->>UserCache: Update cache if user is found from DB

UserService->>UserApi: If user not found, return "unknown user"

UserApi->>Client: Return "unknown user"

UserService->>UserService: If user found, compute hash of password plus salt, compare the computed hash with the saltedHash

UserService->>UserApi: If the two hashes not match, return failure

UserApi->>Client: Return failure

UserService->>UserService: If the two hashes match, generate encrypted token

UserService->>UserApi: return encrypted token

UserApi->>Client: Return encrypted token

Client->>LoadBalancer: CreateWSConnectionRequest

LoadBalancer->>ServiceDiscovery: Pick a ConnectionServer, and route the CreateWSConnectionRequest to it

ConnectionServer->>Client: Verify the encrypted token, and accept the connection

ConnectionServer->>ConnectionManager: put the client/connectionserver info

sequenceDiagram

title Post a tweet

autonumber

Client->>LoadBalancer: PostTweetRequest

LoadBalancer->>TweetApi: PostTweetRequest

TweetApi->>TweetService: PostTweetRequest

TweetService->>UniqueIdGen: generate tweetId

TweetService->>PostTweetMessageQueue: add PostTweetRequest along with tweetId into queue

TweetService->>TweetApi: return success

TweetApi->>Client: return success

loop

TweetWorker->>PostTweetMessageQueue: retrieve message which contains tweetId and PostTweetRequest.

TweetWorker->>ObjDB: if the tweet contains media, use tweetId_m as objId, and insert new row into ObjDB for the contained media.

TweetWorker->>TweetDB: add new row to TweetDB.

TweetWorker->>PostDB: Add new row of uid/tweetId to PostDB

TweetWorker->>FanoutMessageQueue: put uid/tweetid

TweetWorker->>PostTweetMessageQueue: ack message

end

loop

FanoutWorker->>FanoutMessageQueue: retrieve message of uid/tweetid

FanoutWorker->>FolloweeCache: lookup uid to get followers

FanoutWorker->>FolloweeDB: if not found in cache, lookup uid in DB

FanoutWorker->>FollweeCache: update cache if found in DB

FanoutWorker->>CelebrityCache: if uid is a celebrity, add the tweetid to CelebrityCache

FanoutWorker->>FollowerCache: if uid is not a celebrity, add the tweetid to FollowerCache of each follower.

FanoutWorker->>ConnectionManager: for each follower, find the ConnectionServer where the follower is connected

FanoutWorker->>ConnectionServer: send RPC about "new tweets available"

ConnectionServer->>Client: push "new tweets available" to client

FanoutWorker->>FanoutMessageQueue: ack message

end

sequenceDiagram

title User retrieve timeline

autonumber

loop until no timeline data is retrieved

Client->>LoadBalancer: RetrieveTimelineRequest

LoadBalancer->>TweetApi: RetrieveTimelineRequest

TweetApi->>TweetService: RetrieveTimelineRequest

TweetService->>TimelineCache: get the first N tweetIds

TweetService->>TweetCache: for each tweetId, find tweet content

TweetService->>TweetDB: if not found in cache, lookup from DB

TweetService->>TweetCache: update cache if found from DB

TweetService->>TweetApi: compose all the tweet contents along with other necessary info, send them as response

TweetApi->>Client: send the response

end

Submissions

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Submissions

Displaying Solutions with Scores Ranging from 1 to 10