During the benchmark test of ehttpc, we found the gproc's random pool or round-robin pool doesn't scale well.
This PR makes emqx prefer to use the hash pool.
changed:
retainer pool: from random to hash
connector : from random to hash (default)
bridge : from random to hash (default)
authn_http : from random to hash (example)
unchanged:
worker pool type: hash
broker pool type: hash
resource type: hash
exproto type: hash
dashboard type: hash