This change adds 2 new parameters to enable and control concurrent GETs
in swift, these are 'concurrent_gets' and 'concurrency_timeout'.
'concurrent_gets' allows you to turn on or off concurrent GETs, when
on it will set the GET/HEAD concurrency to replica count. And in the
case of EC HEADs it will set it to ndata.
The proxy will then serve only the first valid source to respond.
This applies to all account, container and object GETs except
for EC. For EC only HEAD requests are effected.
It achieves this by changing the request sending mechanism to using
GreenAsyncPile and green threads with a time out between each
request.
'concurrency_timeout' is related to concurrent_gets. And is the
amount of time to wait before firing the next thread. A value of 0
will fire at the same time (fully concurrent), setting another value
will stagger the firing allowing you the ability to give a node a
shorter chance to respond before firing the next. This value is a float
and should be somewhere between 0 and node_timeout. The default is
conn_timeout. Meaning by default it will stagger the firing.
DocImpact
Implements: blueprint concurrent-reads
Change-Id: I789d39472ec48b22415ff9d9821b1eefab7da867
f595a7e704