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changeset 4667:d05ab8793a69 stable-1.2

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Merge of r4622, r4623: balancing changes. *) Upstream: smooth weighted round-robin balancing. For edge case weights like { 5, 1, 1 } we now produce { a, a, b, a, c, a, a } sequence instead of { c, b, a, a, a, a, a } produced previously. Algorithm is as follows: on each peer selection we increase current_weight of each eligible peer by its weight, select peer with greatest current_weight and reduce its current_weight by total number of weight points distributed among peers. In case of { 5, 1, 1 } weights this gives the following sequence of current_weight's: a b c 0 0 0 (initial state) 5 1 1 (a selected) -2 1 1 3 2 2 (a selected) -4 2 2 1 3 3 (b selected) 1 -4 3 6 -3 4 (a selected) -1 -3 4 4 -2 5 (c selected) 4 -2 -2 9 -1 -1 (a selected) 2 -1 -1 7 0 0 (a selected) 0 0 0 To preserve weight reduction in case of failures the effective_weight variable was introduced, which usually matches peer's weight, but is reduced temporarily on peer failures. This change also fixes loop with backup servers and proxy_next_upstream http_404 (ticket #47), and skipping alive upstreams in some cases if there are multiple dead ones (ticket #64). *) Upstream: fixed ip_hash rebalancing with the "down" flag. Due to weight being set to 0 for down peers, order of peers after sorting wasn't the same as without the "down" flag (with down peers at the end), resulting in client rebalancing for clients on other servers. The only rebalancing which should happen after adding "down" to a server is one for clients on the server. The problem was introduced in r1377 (which fixed endless loop by setting weight to 0 for down servers). The loop is no longer possible with new smooth algorithm, so preserving original weight is safe.
author Maxim Dounin <mdounin@mdounin.ru>
date Mon, 04 Jun 2012 11:21:58 +0000
parents 0bb016b1fd2d
children ba2c7463ce18
files src/http/ngx_http_upstream_round_robin.c src/http/ngx_http_upstream_round_robin.h
diffstat 2 files changed, 75 insertions(+), 172 deletions(-) [+]
line wrap: on
line diff
--- a/src/http/ngx_http_upstream_round_robin.c
+++ b/src/http/ngx_http_upstream_round_robin.c
@@ -12,8 +12,8 @@
 
 static ngx_int_t ngx_http_upstream_cmp_servers(const void *one,
     const void *two);
-static ngx_uint_t
-ngx_http_upstream_get_peer(ngx_http_upstream_rr_peers_t *peers);
+static ngx_http_upstream_rr_peer_t *ngx_http_upstream_get_peer(
+    ngx_http_upstream_rr_peer_data_t *rrp);
 
 #if (NGX_HTTP_SSL)
 
@@ -80,8 +80,9 @@ ngx_http_upstream_init_round_robin(ngx_c
                 peers->peer[n].max_fails = server[i].max_fails;
                 peers->peer[n].fail_timeout = server[i].fail_timeout;
                 peers->peer[n].down = server[i].down;
-                peers->peer[n].weight = server[i].down ? 0 : server[i].weight;
-                peers->peer[n].current_weight = peers->peer[n].weight;
+                peers->peer[n].weight = server[i].weight;
+                peers->peer[n].effective_weight = server[i].weight;
+                peers->peer[n].current_weight = 0;
                 n++;
             }
         }
@@ -131,7 +132,8 @@ ngx_http_upstream_init_round_robin(ngx_c
                 backup->peer[n].socklen = server[i].addrs[j].socklen;
                 backup->peer[n].name = server[i].addrs[j].name;
                 backup->peer[n].weight = server[i].weight;
-                backup->peer[n].current_weight = server[i].weight;
+                backup->peer[n].effective_weight = server[i].weight;
+                backup->peer[n].current_weight = 0;
                 backup->peer[n].max_fails = server[i].max_fails;
                 backup->peer[n].fail_timeout = server[i].fail_timeout;
                 backup->peer[n].down = server[i].down;
@@ -190,7 +192,8 @@ ngx_http_upstream_init_round_robin(ngx_c
         peers->peer[i].socklen = u.addrs[i].socklen;
         peers->peer[i].name = u.addrs[i].name;
         peers->peer[i].weight = 1;
-        peers->peer[i].current_weight = 1;
+        peers->peer[i].effective_weight = 1;
+        peers->peer[i].current_weight = 0;
         peers->peer[i].max_fails = 1;
         peers->peer[i].fail_timeout = 10;
     }
@@ -306,7 +309,8 @@ ngx_http_upstream_create_round_robin_pee
         peers->peer[0].socklen = ur->socklen;
         peers->peer[0].name = ur->host;
         peers->peer[0].weight = 1;
-        peers->peer[0].current_weight = 1;
+        peers->peer[0].effective_weight = 1;
+        peers->peer[0].current_weight = 0;
         peers->peer[0].max_fails = 1;
         peers->peer[0].fail_timeout = 10;
 
@@ -338,7 +342,8 @@ ngx_http_upstream_create_round_robin_pee
             peers->peer[i].name.len = len;
             peers->peer[i].name.data = p;
             peers->peer[i].weight = 1;
-            peers->peer[i].current_weight = 1;
+            peers->peer[i].effective_weight = 1;
+            peers->peer[i].current_weight = 0;
             peers->peer[i].max_fails = 1;
             peers->peer[i].fail_timeout = 10;
         }
@@ -378,8 +383,6 @@ ngx_http_upstream_get_round_robin_peer(n
 {
     ngx_http_upstream_rr_peer_data_t  *rrp = data;
 
-    time_t                         now;
-    uintptr_t                      m;
     ngx_int_t                      rc;
     ngx_uint_t                     i, n;
     ngx_connection_t              *c;
@@ -389,8 +392,6 @@ ngx_http_upstream_get_round_robin_peer(n
     ngx_log_debug1(NGX_LOG_DEBUG_HTTP, pc->log, 0,
                    "get rr peer, try: %ui", pc->tries);
 
-    now = ngx_time();
-
     /* ngx_lock_mutex(rrp->peers->mutex); */
 
     if (rrp->peers->last_cached) {
@@ -423,118 +424,15 @@ ngx_http_upstream_get_round_robin_peer(n
 
         /* there are several peers */
 
-        if (pc->tries == rrp->peers->number) {
-
-            /* it's a first try - get a current peer */
-
-            i = pc->tries;
-
-            for ( ;; ) {
-                rrp->current = ngx_http_upstream_get_peer(rrp->peers);
-
-                ngx_log_debug2(NGX_LOG_DEBUG_HTTP, pc->log, 0,
-                               "get rr peer, current: %ui %i",
-                               rrp->current,
-                               rrp->peers->peer[rrp->current].current_weight);
-
-                n = rrp->current / (8 * sizeof(uintptr_t));
-                m = (uintptr_t) 1 << rrp->current % (8 * sizeof(uintptr_t));
-
-                if (!(rrp->tried[n] & m)) {
-                    peer = &rrp->peers->peer[rrp->current];
-
-                    if (!peer->down) {
-
-                        if (peer->max_fails == 0
-                            || peer->fails < peer->max_fails)
-                        {
-                            break;
-                        }
-
-                        if (now - peer->checked > peer->fail_timeout) {
-                            peer->checked = now;
-                            break;
-                        }
-
-                        peer->current_weight = 0;
-
-                    } else {
-                        rrp->tried[n] |= m;
-                    }
-
-                    pc->tries--;
-                }
-
-                if (pc->tries == 0) {
-                    goto failed;
-                }
-
-                if (--i == 0) {
-                    ngx_log_error(NGX_LOG_ALERT, pc->log, 0,
-                                  "round robin upstream stuck on %ui tries",
-                                  pc->tries);
-                    goto failed;
-                }
-            }
+        peer = ngx_http_upstream_get_peer(rrp);
 
-            peer->current_weight--;
-
-        } else {
-
-            i = pc->tries;
-
-            for ( ;; ) {
-                n = rrp->current / (8 * sizeof(uintptr_t));
-                m = (uintptr_t) 1 << rrp->current % (8 * sizeof(uintptr_t));
-
-                if (!(rrp->tried[n] & m)) {
-
-                    peer = &rrp->peers->peer[rrp->current];
-
-                    if (!peer->down) {
-
-                        if (peer->max_fails == 0
-                            || peer->fails < peer->max_fails)
-                        {
-                            break;
-                        }
-
-                        if (now - peer->checked > peer->fail_timeout) {
-                            peer->checked = now;
-                            break;
-                        }
-
-                        peer->current_weight = 0;
-
-                    } else {
-                        rrp->tried[n] |= m;
-                    }
-
-                    pc->tries--;
-                }
-
-                rrp->current++;
-
-                if (rrp->current >= rrp->peers->number) {
-                    rrp->current = 0;
-                }
-
-                if (pc->tries == 0) {
-                    goto failed;
-                }
-
-                if (--i == 0) {
-                    ngx_log_error(NGX_LOG_ALERT, pc->log, 0,
-                                  "round robin upstream stuck on %ui tries",
-                                  pc->tries);
-                    goto failed;
-                }
-            }
-
-            peer->current_weight--;
+        if (peer == NULL) {
+            goto failed;
         }
 
-        rrp->tried[n] |= m;
+        ngx_log_debug2(NGX_LOG_DEBUG_HTTP, pc->log, 0,
+                       "get rr peer, current: %ui %i",
+                       rrp->current, peer->current_weight);
     }
 
     pc->sockaddr = peer->sockaddr;
@@ -545,11 +443,6 @@ ngx_http_upstream_get_round_robin_peer(n
 
     if (pc->tries == 1 && rrp->peers->next) {
         pc->tries += rrp->peers->next->number;
-
-        n = rrp->peers->next->number / (8 * sizeof(uintptr_t)) + 1;
-        for (i = 0; i < n; i++) {
-             rrp->tried[i] = 0;
-        }
     }
 
     return NGX_OK;
@@ -595,56 +488,71 @@ failed:
 }
 
 
-static ngx_uint_t
-ngx_http_upstream_get_peer(ngx_http_upstream_rr_peers_t *peers)
+static ngx_http_upstream_rr_peer_t *
+ngx_http_upstream_get_peer(ngx_http_upstream_rr_peer_data_t *rrp)
 {
-    ngx_uint_t                    i, n, reset = 0;
-    ngx_http_upstream_rr_peer_t  *peer;
-
-    peer = &peers->peer[0];
-
-    for ( ;; ) {
+    time_t                        now;
+    uintptr_t                     m;
+    ngx_int_t                     total;
+    ngx_uint_t                    i, n;
+    ngx_http_upstream_rr_peer_t  *peer, *best;
 
-        for (i = 0; i < peers->number; i++) {
+    now = ngx_time();
 
-            if (peer[i].current_weight <= 0) {
-                continue;
-            }
-
-            n = i;
-
-            while (i < peers->number - 1) {
+    best = NULL;
+    total = 0;
 
-                i++;
+    for (i = 0; i < rrp->peers->number; i++) {
 
-                if (peer[i].current_weight <= 0) {
-                    continue;
-                }
+        n = i / (8 * sizeof(uintptr_t));
+        m = (uintptr_t) 1 << i % (8 * sizeof(uintptr_t));
 
-                if (peer[n].current_weight * 1000 / peer[i].current_weight
-                    > peer[n].weight * 1000 / peer[i].weight)
-                {
-                    return n;
-                }
+        if (rrp->tried[n] & m) {
+            continue;
+        }
 
-                n = i;
-            }
+        peer = &rrp->peers->peer[i];
 
-            if (peer[i].current_weight > 0) {
-                n = i;
-            }
-
-            return n;
+        if (peer->down) {
+            continue;
         }
 
-        if (reset++) {
-            return 0;
+        if (peer->max_fails
+            && peer->fails >= peer->max_fails
+            && now - peer->checked <= peer->fail_timeout)
+        {
+            continue;
+        }
+
+        peer->current_weight += peer->effective_weight;
+        total += peer->effective_weight;
+
+        if (peer->effective_weight < peer->weight) {
+            peer->effective_weight++;
         }
 
-        for (i = 0; i < peers->number; i++) {
-            peer[i].current_weight = peer[i].weight;
+        if (best == NULL || peer->current_weight > best->current_weight) {
+            best = peer;
         }
     }
+
+    if (best == NULL) {
+        return NULL;
+    }
+
+    i = best - &rrp->peers->peer[0];
+
+    rrp->current = i;
+
+    n = i / (8 * sizeof(uintptr_t));
+    m = (uintptr_t) 1 << i % (8 * sizeof(uintptr_t));
+
+    rrp->tried[n] |= m;
+
+    best->current_weight -= total;
+    best->checked = now;
+
+    return best;
 }
 
 
@@ -683,15 +591,15 @@ ngx_http_upstream_free_round_robin_peer(
         peer->checked = now;
 
         if (peer->max_fails) {
-            peer->current_weight -= peer->weight / peer->max_fails;
+            peer->effective_weight -= peer->weight / peer->max_fails;
         }
 
         ngx_log_debug2(NGX_LOG_DEBUG_HTTP, pc->log, 0,
                        "free rr peer failed: %ui %i",
-                       rrp->current, peer->current_weight);
+                       rrp->current, peer->effective_weight);
 
-        if (peer->current_weight < 0) {
-            peer->current_weight = 0;
+        if (peer->effective_weight < 0) {
+            peer->effective_weight = 0;
         }
 
         /* ngx_unlock_mutex(rrp->peers->mutex); */
@@ -705,12 +613,6 @@ ngx_http_upstream_free_round_robin_peer(
         }
     }
 
-    rrp->current++;
-
-    if (rrp->current >= rrp->peers->number) {
-        rrp->current = 0;
-    }
-
     if (pc->tries) {
         pc->tries--;
     }
--- a/src/http/ngx_http_upstream_round_robin.h
+++ b/src/http/ngx_http_upstream_round_robin.h
@@ -20,6 +20,7 @@ typedef struct {
     ngx_str_t                       name;
 
     ngx_int_t                       current_weight;
+    ngx_int_t                       effective_weight;
     ngx_int_t                       weight;
 
     ngx_uint_t                      fails;