Author: mdounin
Date: 2012-06-04 11:21:58 +0000 (Mon, 04 Jun 2012)
New Revision: 4668
URL: http://trac.nginx.org/nginx/changeset/4668/nginx

Log:
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.


Modified:
branches/stable-1.2/
branches/stable-1.2/src/http/ngx_http_upstream_round_robin.c
branches/stable-1.2/src/http/ngx_http_upstream_round_robin.h

Index: branches/stable-1.2
===================================================================
--- branches/stable-1.2 2012-06-04 11:15:46 UTC (rev 4667)
+++ branches/stable-1.2 2012-06-04 11:21:58 UTC (rev 4668)

Property changes on: branches/stable-1.2
___________________________________________________________________
Modified: svn:mergeinfo
## -1 +1 ##
-/trunk:4611-4613,4615-4621,4641
+/trunk:4611-4613,4615-4623,4641
\ No newline at end of property
Modified: branches/stable-1.2/src/http/ngx_http_upstream_round_robin.c
===================================================================
--- branches/stable-1.2/src/http/ngx_http_upstream_round_robin.c 2012-06-04 11:15:46 UTC (rev 4667)
+++ branches/stable-1.2/src/http/ngx_http_upstream_round_robin.c 2012-06-04 11:21:58 UTC (rev 4668)
@@ -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 @@
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 @@
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 @@
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 @@
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 @@
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_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_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 @@

/* there are several peers */

- if (pc->tries == rrp->peers->number) {
+ peer = ngx_http_upstream_get_peer(rrp);

- /* 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->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 @@

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 @@
}


-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;
+ time_t now;
+ uintptr_t m;
+ ngx_int_t total;
+ ngx_uint_t i, n;
+ ngx_http_upstream_rr_peer_t *peer, *best;

- peer = &peers->peer[0];
+ now = ngx_time();

- for ( ;; ) {
+ best = NULL;
+ total = 0;

- for (i = 0; i < peers->number; 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));

- n = i;
+ if (rrp->tried[n] & m) {
+ continue;
+ }

- while (i < peers->number - 1) {
+ peer = &rrp->peers->peer[i];

- i++;
+ if (peer->down) {
+ continue;
+ }

- if (peer[i].current_weight <= 0) {
- continue;
- }
+ if (peer->max_fails
+ && peer->fails >= peer->max_fails
+ && now - peer->checked <= peer->fail_timeout)
+ {
+ continue;
+ }

- if (peer[n].current_weight * 1000 / peer[i].current_weight
- > peer[n].weight * 1000 / peer[i].weight)
- {
- return n;
- }
+ peer->current_weight += peer->effective_weight;
+ total += peer->effective_weight;

- n = i;
- }
-
- if (peer[i].current_weight > 0) {
- n = i;
- }
-
- return n;
+ if (peer->effective_weight < peer->weight) {
+ peer->effective_weight++;
}

- if (reset++) {
- return 0;
+ if (best == NULL || peer->current_weight > best->current_weight) {
+ best = peer;
}
+ }

- for (i = 0; i < peers->number; i++) {
- peer[i].current_weight = peer[i].weight;
- }
+ 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 @@
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 @@
}
}

- rrp->current++;
-
- if (rrp->current >= rrp->peers->number) {
- rrp->current = 0;
- }
-
if (pc->tries) {
pc->tries--;
}

Modified: branches/stable-1.2/src/http/ngx_http_upstream_round_robin.h
===================================================================
--- branches/stable-1.2/src/http/ngx_http_upstream_round_robin.h 2012-06-04 11:15:46 UTC (rev 4667)
+++ branches/stable-1.2/src/http/ngx_http_upstream_round_robin.h 2012-06-04 11:21:58 UTC (rev 4668)
@@ -20,6 +20,7 @@
ngx_str_t name;

ngx_int_t current_weight;
+ ngx_int_t effective_weight;
ngx_int_t weight;

ngx_uint_t fails;

_______________________________________________
nginx-devel mailing list
nginx-devel@nginx.org
http://mailman.nginx.org/mailman/listinfo/nginx-devel