Too many Redis connections: ERR max number of clients reached on Heroku's free tier

[albertkim]

Is your feature request related to a problem? Please describe.
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I use Heroku for Cube.js deployments. If I make 3+ concurrent queries to the server, the app instance will crash with the error ERR max number of clients reached. Heroku's free tier allows for 20 connections at once.

Describe the solution you'd like

As mentioned by Pavel on the Cube.js Slack channel, a connection poll would probably solve this issue to prevent Cube from using more than is available.

Describe alternatives you've considered

The only alternative I can think of is to pay more for Heroku. I've had to go up to Premium 2 to not crash, but I'm worried about what happens when more users are generating reports at the same time.

Additional context
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[paveltiunov]

@albertkim Hey Albert! Thanks for posting this. So sounds like it's Redis connections not database ones?

[albertkim]

@paveltiunov correct.

[paveltiunov]

So the solution is to create redis connection pool here or just reuse non-blocking redis connections. Total count of Redis connections is equal to count of waiting concurrent users + some constant connections count used to retrieve cache. Redis itself is capable of handling thousands of concurrent connections. For Heroku it's merely a pay wall. You can consider using Redis services without connection limit like https://www.compose.com/pricing#redis.

If there's only single instance of Cube.js server then you can consider running Cube.js without Redis at all: https://cube.dev/docs/deployment#production-mode-running-without-redis

[0x62]

Getting this issue with the latest version. Looks like Redis polling has been merged, has it made it to live release yet?

[paveltiunov]

@0x62 Hey Ben! Yep. It's live. However by default there're 1000 max connections for backward compatibility. Please see: https://cube.dev/docs/deployment#production-mode-redis-pool