[nginx] Core: reusing connections in advance.

[Maxim Dounin]

details:   https://hg.nginx.org/nginx/rev/5440ff4ac6fc
branches:  
changeset: 7698:5440ff4ac6fc
user:      Maxim Dounin <mdounin at mdounin.ru>
date:      Mon Aug 10 18:53:07 2020 +0300
description:
Core: reusing connections in advance.

Reworked connections reuse, so closing connections is attempted in
advance, as long as number of free connections is less than 1/16 of
worker connections configured.  This ensures that new connections can
be handled even if closing a reusable connection requires some time,
for example, for a lingering close (ticket #2017).

The 1/16 ratio is selected to be smaller than 1/8 used for disabling
accept when working with accept mutex, so nginx will try to balance
new connections to different workers first, and will start reusing
connections only if this won't help.

diffstat:

 src/core/ngx_connection.c |  11 +++++------
 1 files changed, 5 insertions(+), 6 deletions(-)

diffs (29 lines):

diff -r b9071b875194 -r 5440ff4ac6fc src/core/ngx_connection.c
--- a/src/core/ngx_connection.c	Mon Aug 10 18:52:59 2020 +0300
+++ b/src/core/ngx_connection.c	Mon Aug 10 18:53:07 2020 +0300
@@ -1107,12 +1107,9 @@ ngx_get_connection(ngx_socket_t s, ngx_l
         return NULL;
     }
 
-    c = ngx_cycle->free_connections;
+    ngx_drain_connections((ngx_cycle_t *) ngx_cycle);
 
-    if (c == NULL) {
-        ngx_drain_connections((ngx_cycle_t *) ngx_cycle);
-        c = ngx_cycle->free_connections;
-    }
+    c = ngx_cycle->free_connections;
 
     if (c == NULL) {
         ngx_log_error(NGX_LOG_ALERT, log, 0,
@@ -1298,7 +1295,9 @@ ngx_drain_connections(ngx_cycle_t *cycle
     ngx_queue_t       *q;
     ngx_connection_t  *c;
 
-    if (cycle->reusable_connections_n == 0) {
+    if (cycle->free_connection_n > cycle->connection_n / 16
+        || cycle->reusable_connections_n == 0)
+    {
         return;
     }