CODEWITHSUNDEEP
javascriptsqlajaxchat
BillO
BillO

Reputation: 15

Refresh rate for AJAX chat application

I am developing a website which, among other things, allows users to chat in real time with one another (similar to Facebook chat). Messages are stored in MySQL table messages, which contains ID of the message, sender ID, receiver ID and time.

When user A is chatting with user B, I get all their messages by SQL statement SELECT * FROM messages WHERE (senderID='userA' AND receiverID='userB') OR (senderId='userB' AND receiverID='userA'). This statement retrieves all the messages between user A and user B.

When chat is opened, I send an AJAX request every second (should it be less/more?) to check if there are any new messages between these two users in the database.

My questions are:

Upvotes: 0

Views: 657

Answers (1)

nicholaswmin
nicholaswmin

Reputation: 22989

You should really use WebSockets for this but if you really want to go with polling this is how you could do it:

Your system should hold Conversations, Users or Participants and Messages.

  • When John starts a conversation for the 1st time with Mary, you create a new Conversation, with a unique conversation_id. The Participants to that conversation are Mary and John.

  • When a user first opens a past Conversation, you SELECT * FROM messages WHERE conversation_id = 'xyz'.

  • From then on when John sends a message to Mary you simply INSERT that message in your database.

  • When Mary sends the next polling signal she includes in her message the last message_id she received. This allows you to SELECT * FROM messages WHERE message_id > 115 AND conversation_id = xyz.

  • Mary then appends to her existing list of messages the new messages.

This assumes that message_id is an auto incremented column.

Other pointers:

  • Prefer WebSockets over long-polling. They are more efficient because communication between server/clients happens only when needed, i.e when a message is sent.
  • Prefer a non-blocking server technology, like NodeJS. Chat applications revolve around small data being sent extremely frequently back and forth. Traditional server technologies like PHP don't deal well with these circumstances.

Upvotes: 3

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