[Question] What's does `pool_max_idle_per_host` do?

[morrisonlevi]

The documentation for pool_max_idle_per_host on the builder says:

Sets the maximum idle connection per host allowed in the pool.

I'm still not sure what this actually does though. For instance, what if I set it to 0? What does that mean?

I'm asking because I recently hit cases where every 2nd request to the same host would have a broken pipe. Searching around suggested that pool_max_idle_per_host(0) could fix it, and it seems to do the trick. However, I'm not sure why. Does this mean connections aren't pooled at all when set to 0? How is this different from making a new client on every request? Are there any downsides you can think of to setting this?