Question: reusing Redis bclient

[yulianovdey]

Hello!

In PATTERNS.md it says that bull requires 3 connections, and lists two types - client and server subscriber. I noticed that there's also a bclient type that gets passed to createClient. Can this connection be reused as well, or is that not advised?

Thanks in advance!

[ritter]

From my experience, bclient was not shareable. Bull degraded terribly when I tried to share that redis connection.

The 3 types I've seen are client, subscriber, and bclient ... I've never seen server.

[yulianovdey]

@ritter Good to know, thanks. Also you're right; I definitely meant subscriber.

[manast]

bclient cannot be shared because it is the client used for blocking calls, so if one instance for instance blocks it waiting for jobs to arrive to the queue, all the other instance sharing it will stall.

[yulianovdey]

@manast Makes sense, thanks for the super fast reply!

[ritter]

In regards to sharing redis connections, we are sharing client connections, and subscriber with other subscribers, but every bclient gets its own connection.

[joshuapaling]

Bit of extra info for future readers: the relevant source is at https://github.com/OptimalBits/bull/blob/develop/lib/queue.js#L1098

    return this.bclient
      .brpoplpush(this.keys.wait, this.keys.active, this.settings.drainDelay)

When a queue is empty, that queue opens a blocking connection to redis to wait for the next item to be added to the queue. That connection is then kept around as "the blocking connection to use next time this same queue is empty". Hence the need for one blocking connection per queue.

I've opened up a PR to make this more clear in the example code for re-using connections: #1714