more connections are created in the pool than configured

[akostadinov]

As far as I see the connection pool limit is not enforced precisely. With the attached test script, which runs 100 of concurrent async tasks and a pool limit of 10, I see like 19 connections actually established.

test_async_redis_pool.rb.gz

Script is a little weird for being AI generated but I fixed up the important parts. So for example I set a limit of 10 and the script actually generates 19 connections. Also I noticed this with redis so it is redis based.

Statistics:
  Total tasks created: 432
  Total operations: 432
  Total errors: 0
  Duration: 18.61 seconds
  Operations/sec: 23.21

Connection Pool Information:
  Max connections configured: 10
  Current pool size: 19

I pin the issue down to the default concurrency option of Async::Pool::Controller

It is limit || 1 which would almost certainly create more than the requested limit under high load.

I think that the solution to prevent user surprise can be one of the following:

• change the default concurrency to one, with such setting the limit is being properly enforced + document that a higher concurrency may result in more resources created than expected
• make sure concurrency is adjusted based on the existing number of resources such that it never exceeds the specified max number

Of course the the latter solution would be much preferable.

P.S. Also I see an old issue socketry/async-redis#20 where op observed more and more resources being created when there is no limit. I'm not sure why this happens but I also observed something similar. Maybe that should be a separate issue but not sure whether it might be addressed here or in async-redis.