Hello, I’ve recently developed a module that creates distributed user counters, based on what’s described in this post Basically, locally I use ETS table to atomically know how many people there is in a channel, then I aggregate all counters of all nodes using Phoenix Tracker. In summary, users s…

Your remarks make it sound like there’s no real reason for the number 70 exactly, so I’d suggest not going with a fixed cutoff point, but rather evalute a solution using low and high watermarks. Start creating new channels at a low watermark, but also make it so only the high watermark makes that nu…

Is there a reason you’re using ETS instead of Redis? You can use Phoenix Presence and push joins/leaves to Redis directly. Here’s an example of using Redis to track users and user counts. SADD/SREM handle adding/removing users to a set, while INCRBY/DECRBY update the count. def handle_metas(topi…

Hello Is there a reason you’re using ETS instead of Redis? I use ETS because it’s really fast in atomic operations. I’m able to spread hundreds of thousands of users connecting at the same time within seconds among those topics. if you want to assign users to room* topics, you could also use …

If you want to use ETS that’s fine, I was just pointing out that Redis is designed to handle what you’re trying to do in a way that ETS and Genservers are not. Your trying to add cross node functionality to tools that are for local use, rather than use a tool that will work cross node by default. …

If you were using a sorted set you wouldn’t be making this post because it solves the exact issue your post is about with regards to counting and distributing users to rooms atomically. So you saying that if I use redis I could get the current count for a channel across all nodes, while hundreds …

[image] Phxie: I should also add, one of the reasons I’m pushing Redis so hard is that I was desgning something with ETS/Genservers a year or so ago for a couple of week before I hit a wall and finally tried Redis. Redis made everything 10x easier for me. The big change here is not GenServer …

Yes that’s what I think, and I don’t see how I could have a performant algorithm if I have to get the updated global counter value from redis ? I think what you said early makes sense. I need to make some compromise regarding that max value, and probably accept that at certain moments, the counter…

[image] jaybe78: So you saying that if I use redis I could get the current count for a channel across all nodes, while hundreds of thousands of users are joining ? Yes. Redis can give you an atomic, cross‑node count while users join and leave in real time. It won’t match ETS’s raw speed, but…

Don’t take it personal dude. :smiley: I haven’t said what you say is wrong. I’m just asking questions. :slight_smile: Concerning Redis I thought about using it. I use AWS, so I could use it but it’s really expensive. I could deploy my own redis, but at this point I don’t feel like managing my o…

Implementing distributed user counters

Questions & Help Questions

LostKobrakai June 13, 2025, 1:31pm 9

The big change here is not GenServer vs. Redis though. It’s centralized storage of data (CP) vs. distributed storage of data (eventual consistency / AP)