details: http://hg.nginx.org/nginx/rev/426828549afc
branches:
changeset: 6873:426828549afc
user: Maxim Dounin <mdounin@mdounin.ru>
date: Fri Jan 20 14:03:20 2017 +0300
description:
Improved connection draining with small number of connections.

Closing up to 32 connections might be too aggressive if worker_connections
is set to a comparable number (and/or there are only a small number of
reusable connections). If an occasional connection shorage happens in
such a configuration, it leads to closing all reusable connections instead
of gradually reducing keepalive timeout to a smaller value. To improve
granularity in such configurations we now close no more than 1/8 of all
reusable connections at once.

Suggested by Joel Cunningham.

diffstat:

src/core/ngx_connection.c | 8 ++++++--
src/core/ngx_cycle.h | 1 +
2 files changed, 7 insertions(+), 2 deletions(-)

diffs (46 lines):

diff --git a/src/core/ngx_connection.c b/src/core/ngx_connection.c
--- a/src/core/ngx_connection.c
+++ b/src/core/ngx_connection.c
@@ -1204,6 +1204,7 @@ ngx_reusable_connection(ngx_connection_t

if (c->reusable) {
ngx_queue_remove(&c->queue);
+ ngx_cycle->reusable_connections_n--;

#if (NGX_STAT_STUB)
(void) ngx_atomic_fetch_add(ngx_stat_waiting, -1);
@@ -1217,6 +1218,7 @@ ngx_reusable_connection(ngx_connection_t

ngx_queue_insert_head(
(ngx_queue_t *) &ngx_cycle->reusable_connections_queue, &c->queue);
+ ngx_cycle->reusable_connections_n++;

#if (NGX_STAT_STUB)
(void) ngx_atomic_fetch_add(ngx_stat_waiting, 1);
@@ -1228,11 +1230,13 @@ ngx_reusable_connection(ngx_connection_t
static void
ngx_drain_connections(ngx_cycle_t *cycle)
{
- ngx_int_t i;
+ ngx_uint_t i, n;
ngx_queue_t *q;
ngx_connection_t *c;

- for (i = 0; i < 32; i++) {
+ n = ngx_max(ngx_min(32, cycle->reusable_connections_n / 8), 1);
+
+ for (i = 0; i < n; i++) {
if (ngx_queue_empty(&cycle->reusable_connections_queue)) {
break;
}
diff --git a/src/core/ngx_cycle.h b/src/core/ngx_cycle.h
--- a/src/core/ngx_cycle.h
+++ b/src/core/ngx_cycle.h
@@ -53,6 +53,7 @@ struct ngx_cycle_s {
ngx_uint_t modules_used; /* unsigned modules_used:1; */

ngx_queue_t reusable_connections_queue;
+ ngx_uint_t reusable_connections_n;

ngx_array_t listening;
ngx_array_t paths;
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