improve the first selection of SWRR algorithm

[陈洁 Cjhust Chen]

Hi:
     We improve the Smooth Weighted Round-Robin（SWRR） algorithm to successfully resolve the problem in the following situations.

Situation 1：
upstream backend-server {
     server 1.1.1.1:8000  weight=100;
     server 2.2.2.2:8000  weight=101;
     server 3.3.3.3:8000  weight=100;
}

1. When each machine in the cluster mode executes "-s reload" at the same time , the first selection of each machine is the machine 2.2.2.2:8000 having higher weight , which will lead to 300%+ increase of 2.2.2.2:8000 traffic.
2. More and more companies are implementing service discovery based on nginx. Adding or removing machine will also lead to 300%+ increase of 2.2.2.2:8000 traffic.



Situation 2：
upstream backend-server {
     server 1.1.1.1:8000  weight=100;
     server 2.2.2.2:8000  weight=100;
     server 3.3.3.3:8000  weight=100;
}

1. When each machine in the cluster mode executes "-s reload" at the same time , the first selection of each machine is the first machine 1.1.1.1:8000, which will lead to 300%+ increase of 1.1.1.1:8000 traffic.
2. More and more companies are implementing service discovery based on nginx. Adding or removing machine will also lead to 300%+ increase of 1.1.1.1:8000 traffic.





# HG changeset patch
# User Jie Chen <cherrychenjie at didiglobal.com<mailto:cherrychenjie at didiglobal.com>>
# Date 1599813602 -28800
#      Fri Sep 11 16:40:02 2020 +0800
# Node ID 931b0c055626657d68f886781c193ffb09245a2e
# Parent  da5e3f5b16733167142b599b6af3ce9469a07d52
improve the first selection of SWRR algorithm

diff -r da5e3f5b1673 -r 931b0c055626 src/http/ngx_http_upstream_round_robin.c
--- a/src/http/ngx_http_upstream_round_robin.c  Wed Sep 02 23:13:36 2020 +0300
+++ b/src/http/ngx_http_upstream_round_robin.c  Fri Sep 11 16:40:02 2020 +0800
@@ -91,7 +91,7 @@
                 peer[n].name = server[i].addrs[j].name;
                 peer[n].weight = server[i].weight;
                 peer[n].effective_weight = server[i].weight;
-                peer[n].current_weight = 0;
+                peer[n].current_weight = 0 - ngx_random() % peers->total_weight;
                 peer[n].max_conns = server[i].max_conns;
                 peer[n].max_fails = server[i].max_fails;
                 peer[n].fail_timeout = server[i].fail_timeout;
@@ -155,7 +155,7 @@
                 peer[n].name = server[i].addrs[j].name;
                 peer[n].weight = server[i].weight;
                 peer[n].effective_weight = server[i].weight;
-                peer[n].current_weight = 0;
+                peer[n].current_weight = 0 - ngx_random() % peers->total_weight;
                 peer[n].max_conns = server[i].max_conns;
                 peer[n].max_fails = server[i].max_fails;
                 peer[n].fail_timeout = server[i].fail_timeout;





Thanks~
cherrychenjie at didiglobal.com<mailto:cherrychenjie at didiglobal.com>






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