This Happy Eyeballs (RFC 8305) tuning directive specifies the
minimum delay between opening spare to-server connections (to any
server; i.e. across all concurrent master transactions in a Squid
instance). Each SMP worker currently multiplies the configured gap
by the total number of workers so that the combined spare connection
opening rate of a Squid instance obeys the configured limit. The
workers do not coordinate connection openings yet; a micro burst
of spare connection openings may violate the configured gap.
This directive has similar trade-offs as
happy_eyeballs_connect_timeout, but its focus is on limiting traffic
amplification effects for Squid as a whole, while
happy_eyeballs_connect_timeout works on an individual master
transaction level.
The following Happy Eyeballs directives place additional connection
opening restrictions: happy_eyeballs_connect_timeout and
happy_eyeballs_connect_limit. See the former for related terminology.