MEDIUM: backend: Allow redispatch on retry intervals
For backend load balancing it sometimes makes sense to redispatch rather
than retrying against the same server. For example, when machines or routers
fail you may not want to waste time retrying against a dead server and
would instead prefer to immediately redispatch against other servers.
This patch allows backend sections to specify that they want to
redispatch on a particular interval. If the interval N is positive the
redispatch occurs on every Nth retry, and if the interval N is negative then
the redispatch occurs on the Nth retry prior to the last retry (-1 is the
default and maintains backwards compatibility). In low latency environments
tuning this setting can save a few hundred milliseconds when backends fail.
diff --git a/src/stream.c b/src/stream.c
index 23f7f51..4d62c71 100644
--- a/src/stream.c
+++ b/src/stream.c
@@ -624,7 +624,9 @@
}
/* If the "redispatch" option is set on the backend, we are allowed to
- * retry on another server for the last retry. In order to achieve this,
+ * retry on another server. By default this redispatch occurs on the
+ * last retry, but if configured we allow redispatches to occur on
+ * configurable intervals, e.g. on every retry. In order to achieve this,
* we must mark the stream unassigned, and eventually clear the DIRECT
* bit to ignore any persistence cookie. We won't count a retry nor a
* redispatch yet, because this will depend on what server is selected.
@@ -634,10 +636,15 @@
* we don't care about this particular server.
*/
if (objt_server(s->target) &&
- (si->conn_retries == 0 ||
+ (s->be->options & PR_O_REDISP) && !(s->flags & SF_FORCE_PRST) &&
+ ((((s->be->redispatch_after > 0) &&
+ ((s->be->conn_retries - si->conn_retries) %
+ s->be->redispatch_after == 0)) ||
+ ((s->be->redispatch_after < 0) &&
+ ((s->be->conn_retries - si->conn_retries) %
+ (s->be->conn_retries + 1 + s->be->redispatch_after) == 0))) ||
(!(s->flags & SF_DIRECT) && s->be->srv_act > 1 &&
- ((s->be->lbprm.algo & BE_LB_KIND) == BE_LB_KIND_RR))) &&
- s->be->options & PR_O_REDISP && !(s->flags & SF_FORCE_PRST)) {
+ ((s->be->lbprm.algo & BE_LB_KIND) == BE_LB_KIND_RR)))) {
sess_change_server(s, NULL);
if (may_dequeue_tasks(objt_server(s->target), s->be))
process_srv_queue(objt_server(s->target));