Defines the number of milliseconds before an ajax request is issued. Delayed
requests are only queued after the delay intervall, so another non-delayed
request that is triggered after the delayed request can be queued before the
delayed request. Still, delayed requests block queue space.
- the queue size is set to x,
- n requests are already queued and
- m requests are already delayed
then we have got x-n-m free queue slots.
If a request comes in and the queue is full (x-n-m==0) then one delayed request
is cancelled to make room for the new request. If no request is delayed (m==0)
then one queued request is cancelled to make room for the new request. If
several requests were delayed (m>1) the request to cancel is chosen