From: Marek Vavrusa <marek@vavrusa.com>
Date: Mon, 18 Apr 2016 00:29:41 +0000 (-0700)
Subject: engine: throttle outbound queries only when busy
X-Git-Tag: v1.0.0~30
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=0b02bf5fe9dc02378d719b491984b72b12cac6a4;p=thirdparty%2Fknot-resolver.git

engine: throttle outbound queries only when busy

resolver will always attempt to contact upstreams
known to be bad if it's not busy.
this fixes a problem on low-volume resolvers
where a short connection outage could make
resolvers deny resolving queries even after the
connection is restored
---

diff --git a/daemon/engine.h b/daemon/engine.h
index 5e8e12e95..7c9379939 100644
--- a/daemon/engine.h
+++ b/daemon/engine.h
@@ -29,6 +29,9 @@
 #ifndef RECVMMSG_BATCH
 #define RECVMMSG_BATCH 4
 #endif
+#ifndef QUERY_RATE_THRESHOLD
+#define QUERY_RATE_THRESHOLD (2 * MP_FREELIST_SIZE) /**< Nr of parallel queries considered as high rate */
+#endif
 
 /*
  * @internal These are forward decls to allow building modules with engine but without Lua.
diff --git a/daemon/worker.c b/daemon/worker.c
index 736338d56..5bdd7c2a6 100644
--- a/daemon/worker.c
+++ b/daemon/worker.c
@@ -287,6 +287,10 @@ static struct qr_task *qr_task_create(struct worker_ctx *worker, uv_handle_t *ha
 	kr_resolve_begin(&task->req, &engine->resolver, answer);
 	worker->stats.concurrent += 1;
 	worker->stats.queries += 1;
+	/* Throttle outbound queries only when high pressure */
+	if (worker->stats.concurrent < QUERY_RATE_THRESHOLD) {
+		task->req.options |= QUERY_NO_THROTTLE;
+	}
 	return task;
 }