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Comment by bontoJR | Hacker News Reader

Yes, with Postgres (which I am most confident to talk about), most precisely using PostGIS, you can do that in a matter of hours using it for geo-queries and indexing for getting important stuff (new, trending, etc...). Plus Postgres is supported basically everywhere in any tech stack. I still don't get one point, why people totally ignore SQL dbs by default with new products? I know MongoBD, RethinkDB, CouchDB, etc... are really fascinating solutions, but why not considering SQL eliminating it by default? I am just curios.

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That's only needed for the coordination... that said, it would be easy enough to segment channels based on a certain precision of geohash... messages sent target 9 channels, your current and neighboring channels... you subscribe to the channel you are in, and this updates every N seconds.

Channel position/calculation can happen client side, and subscribe/unsubscribe can happen server-side. Though that may leave room for unscrupulous behavior, it could be locked down a bit more by moving sub/unsub server-side.

The issue will be growth/routing/rerouting of channel data... even then, you can get pretty far with RabbitMQ backed socket.io ... you might need to custom create something before hitting 10M simultaneous users, which at current growth rate would be an issue anyway.

I think its because the only really viable scaling option for Postgres is vertical scaling. Even just setting up any sort of replication with automatic failover is still a pain (multimaster is not yet built in, master-slave also needs 3rd party failover program...)

So, how large would his application have to get before that became a problem?

Replication with automatic failover? I'd go for it immediately, unless you are okay with long downtime and some data loss in case the server goes down.

But if you can live with that, then yes, you're unlikely to have actual scaling problems - at least not for projects like the OP.

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