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changeset 6366:2e5c027f2a98

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Resolver: per-request DNS server balancer. Previously, a global server balancer was used to assign the next DNS server to send a query to. That could lead to a non-uniform distribution of servers per request. A request could be assigned to the same dead server several times in a row and wait longer for a valid server or even time out without being processed. Now each query is sent to all servers sequentially in a circle until a response is received or timeout expires. Initial server for each request is still globally balanced.
author Roman Arutyunyan <arut@nginx.com>
date Thu, 28 Jan 2016 15:28:20 +0300
parents d35b4d590b2d
children 5a16d40c63de
files src/core/ngx_resolver.c src/core/ngx_resolver.h
diffstat 2 files changed, 17 insertions(+), 5 deletions(-) [+]
line wrap: on
line diff
--- a/src/core/ngx_resolver.c
+++ b/src/core/ngx_resolver.c
@@ -685,6 +685,11 @@ ngx_resolve_name_locked(ngx_resolver_t *
         return NGX_OK;
     }
 
+    rn->last_connection = r->last_connection++;
+    if (r->last_connection == r->connections.nelts) {
+        r->last_connection = 0;
+    }
+
     rn->naddrs = (u_short) -1;
 #if (NGX_HAVE_INET6)
     rn->naddrs6 = r->ipv6 ? (u_short) -1 : 0;
@@ -897,6 +902,11 @@ ngx_resolve_addr(ngx_resolver_ctx_t *ctx
         goto failed;
     }
 
+    rn->last_connection = r->last_connection++;
+    if (r->last_connection == r->connections.nelts) {
+        r->last_connection = 0;
+    }
+
     rn->naddrs = (u_short) -1;
 #if (NGX_HAVE_INET6)
     rn->naddrs6 = (u_short) -1;
@@ -1098,11 +1108,7 @@ ngx_resolver_send_query(ngx_resolver_t *
     ngx_resolver_connection_t  *rec;
 
     rec = r->connections.elts;
-
-    rec = &rec[r->last_connection++];
-    if (r->last_connection == r->connections.nelts) {
-        r->last_connection = 0;
-    }
+    rec = &rec[rn->last_connection];
 
     if (rec->udp == NULL) {
 
@@ -1244,6 +1250,10 @@ ngx_resolver_resend(ngx_resolver_t *r, n
 
         if (rn->waiting) {
 
+            if (++rn->last_connection == r->connections.nelts) {
+                rn->last_connection = 0;
+            }
+
             (void) ngx_resolver_send_query(r, rn);
 
             rn->expire = now + r->resend_timeout;
--- a/src/core/ngx_resolver.h
+++ b/src/core/ngx_resolver.h
@@ -93,6 +93,8 @@ typedef struct {
     time_t                    valid;
     uint32_t                  ttl;
 
+    ngx_uint_t                last_connection;
+
     ngx_resolver_ctx_t       *waiting;
 } ngx_resolver_node_t;