CODEWITHSUNDEEP
pythonredis
SangminKim
SangminKim

Reputation: 9136

How does redis publish work?

Suppose that there is one redis-client which is subscribing to channel c1 and another redis-client publishes "data" to channel c1.

At this point, does the data published is pending in a redis-server by when the client subscribing to "c1" get the data(by calling pubsub.listen() or pubsub.get_message()) or go directly to the client subscribing to the channel c1 through a redis-server?

In other words, When a redis-client call pubsub.getMessage() or pubsub.listen(), does redis-client send a request to redis-server to get data or just get data from the local socket buffer?

When I read some documents it is saying that pubsub.get_message() use select module for a socket internally.

It seems to mean that the data subscribed already is in the client local buffer, not server.

Could you give me any suggestion?

Upvotes: 0

Views: 771

Answers (2)

Matías Fidemraizer
Matías Fidemraizer

Reputation: 64923

Redis pubsub is fire and forget.

In other words, when a publish command is sent, the message is received by online subscribers, and who wasn't subscribed/listening for messages when the publish command was sent, won't never get these messages.

Upvotes: 1

Sergio Tulentsev
Sergio Tulentsev

Reputation: 230346

When a client does PUBLISH, this command immediately pushes the message into all sockets that are interested in it. The message is not stored in redis. If a client wasn't subscribed at the time of publishing, he will never see the message.

I'm not familiar with python driver for redis, but judging from the names, I'd guess that listen sends a SUBSCRIBE command and get_message takes a message from the local buffer.

Upvotes: 3

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