Selecting a database on re-connect - discussion

[cloudhead]

I'd like to have an opinion on this issue:

I use different clients for different databases, and so I select the database I want when the client is first created. Sometimes, connections get dropped, and so the selected database is no longer selected on reconnect. Of course, I could call select before each command, but that seems like a huge waste. So ideally, the command would be run every time the client connects.

Because of the way node_redis works though, commands sent from the "connect" event listener will be sent after commands which were sent while offline, this is because of the offline_queue, and the fact that ready is set after "connect" is emitted, so commands in the listener are queued!

The "ready" event is then emitted after all this, but at that point the offline commands are already sent, with the wrong database selected.

The solution I'm currently using, which seems to work is:

  client.on('connect', function () {
      client.send_anyway = true;
      client.select(DB);
      client.send_anyway = false;
  });

This makes it so the select skips the ready-check, and sends the command before the offline_queue is sent.

Here's where this is all happening:

https://github.com/mranney/node_redis/blob/master/index.js#L187

A nice solution would be to emit "connect" after ready = true. Another solution would be to have another event there, like "connected", which gets emitted after we're ready, but before the queue is sent.

Thoughts?

[tisba]

In fact, currently you need to select the db on the error event. Otherwise you risk that your select command get's queued behind other commands in the offline_queue which is reseted while handling error (see e.g. https://github.com/mranney/node_redis/blob/master/index.js#L108). It took me a while to figure out what's the best way to ensure that you only write to a specific db.

I think there should be way to insert a command into the offline queue, before all other events.

[ciaranj]

Hmm, this has also just bitten me. Are there any other stateful-persistent commands that can be sent to a redis server? .. I, like you @cloudhead use the same pattern of 1 client per DB .. and it took me an age to work out why my data wasn't coming back! :)

[mranney]

Hey guys, we still need to fix this for subscribe events, but I think the db re-selection issue is fixed in v0.7.0.

@cloudhead, can you see if this fixes your issue?

[maritz]

It's fixed for me. (ran into the same issue and thought I was already using v0.7.1, turns out I didn't)

Now, the other question is why I'm constantly losing my redis connection?! :/