When threads are enabled and running on a machine with multiple CCX
or multiple nodes, thread groups are now enabled since 3.3-dev2, causing
load-balancing algorithms to randomly fail due to incoming connections
spreading over multiple groups and using different load balancing indexes.
Let's just force "thread-groups 1" into all configs when threads are
enabled to avoid this.
This test brought by commit 8ed1e91efd ("MEDIUM: lb-chash: add directive
hash-preserve-affinity") seems to have hit a limitation of what can be
expressed in vtc, as it would be desirable to have one server response
release two clients at once but the various attempts using barriers
have failed so far. The test seems to work fine locally but still fails
almost 100% of the time on the CI, so it remains timing dependent in
some ways. Tests have been done with nbthread 1, pool-idle-shared off,
http-reuse never (since always fails locally) etc but to no avail. Let's
just mark it broken in case we later figure another way to fix it. It's
still usable locally most of the time, though.
When using hash-based load balancing, requests are always assigned to
the server corresponding to the hash bucket for the balancing key,
without taking maxconn or maxqueue into account, unlike in other load
balancing methods like 'first'. This adds a new backend directive that
can be used to take maxconn and possibly maxqueue in that context. This
can be used when hashing is desired to achieve cache locality, but
sending requests to a different server is preferable to queuing for a
long time or failing requests when the initial server is saturated.
By default, affinity is preserved as was the case previously. When
'hash-preserve-affinity' is set to 'maxqueue', servers are considered
successively in the order of the hash ring until a server that does not
have a full queue is found.
When 'maxconn' is set on a server, queueing cannot be disabled, as
'maxqueue=0' means unlimited. To support picking a different server
when a server is at 'maxconn' irrespective of the queue,
'hash-preserve-affinity' can be set to 'maxconn'.
