[nginx] Upstream hash: limited number of tries in consistent case.

[Maxim Dounin]

details:   http://hg.nginx.org/nginx/rev/6c52b24fcf8e
branches:  
changeset: 7123:6c52b24fcf8e
user:      Maxim Dounin <mdounin at mdounin.ru>
date:      Thu Oct 05 17:42:59 2017 +0300
description:
Upstream hash: limited number of tries in consistent case.

While this may result in non-ideal distribution of requests if nginx
won't be able to select a server in a reasonable number of attempts,
this still looks better than severe performance degradation observed
if there is no limit and there are many points configured (ticket #1030).
This is also in line with what we do for other hash balancing methods.

diffstat:

 src/http/modules/ngx_http_upstream_hash_module.c |  10 +++++++---
 src/stream/ngx_stream_upstream_hash_module.c     |  10 +++++++---
 2 files changed, 14 insertions(+), 6 deletions(-)

diffs (56 lines):

diff --git a/src/http/modules/ngx_http_upstream_hash_module.c b/src/http/modules/ngx_http_upstream_hash_module.c
--- a/src/http/modules/ngx_http_upstream_hash_module.c
+++ b/src/http/modules/ngx_http_upstream_hash_module.c
@@ -503,6 +503,11 @@ ngx_http_upstream_get_chash_peer(ngx_pee
 
     ngx_http_upstream_rr_peers_wlock(hp->rrp.peers);
 
+    if (hp->tries > 20 || hp->rrp.peers->single) {
+        ngx_http_upstream_rr_peers_unlock(hp->rrp.peers);
+        return hp->get_rr_peer(pc, &hp->rrp);
+    }
+
     pc->cached = 0;
     pc->connection = NULL;
 
@@ -577,10 +582,9 @@ ngx_http_upstream_get_chash_peer(ngx_pee
         hp->hash++;
         hp->tries++;
 
-        if (hp->tries >= points->number) {
-            pc->name = hp->rrp.peers->name;
+        if (hp->tries > 20) {
             ngx_http_upstream_rr_peers_unlock(hp->rrp.peers);
-            return NGX_BUSY;
+            return hp->get_rr_peer(pc, &hp->rrp);
         }
     }
 
diff --git a/src/stream/ngx_stream_upstream_hash_module.c b/src/stream/ngx_stream_upstream_hash_module.c
--- a/src/stream/ngx_stream_upstream_hash_module.c
+++ b/src/stream/ngx_stream_upstream_hash_module.c
@@ -505,6 +505,11 @@ ngx_stream_upstream_get_chash_peer(ngx_p
 
     ngx_stream_upstream_rr_peers_wlock(hp->rrp.peers);
 
+    if (hp->tries > 20 || hp->rrp.peers->single) {
+        ngx_stream_upstream_rr_peers_unlock(hp->rrp.peers);
+        return hp->get_rr_peer(pc, &hp->rrp);
+    }
+
     pc->connection = NULL;
 
     now = ngx_time();
@@ -578,10 +583,9 @@ ngx_stream_upstream_get_chash_peer(ngx_p
         hp->hash++;
         hp->tries++;
 
-        if (hp->tries >= points->number) {
-            pc->name = hp->rrp.peers->name;
+        if (hp->tries > 20) {
             ngx_stream_upstream_rr_peers_unlock(hp->rrp.peers);
-            return NGX_BUSY;
+            return hp->get_rr_peer(pc, &hp->rrp);
         }
     }