view src/event/ngx_event_mutex.c @ 4207:4fc91bae6f83

Better recheck of dead upstream servers. Previously nginx used to mark backend again as live as soon as fail_timeout passes (10s by default) since last failure. On the other hand, detecting dead backend takes up to 60s (proxy_connect_timeout) in typical situation "backend is down and doesn't respond to any packets". This resulted in suboptimal behaviour in the above situation (up to 23% of requests were directed to dead backend with default settings). More detailed description of the problem may be found here (in Russian): http://mailman.nginx.org/pipermail/nginx-ru/2011-August/042172.html Fix is to only allow one request after fail_timeout passes, and mark backend as "live" only if this request succeeds. Note that with new code backend will not be marked "live" unless "check" request is completed, and this may take a while in some specific workloads (e.g. streaming). This is believed to be acceptable.
author Maxim Dounin <mdounin@mdounin.ru>
date Wed, 12 Oct 2011 14:22:48 +0000
parents a88a3e4e158f
children d620f497c50f
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/*
 * Copyright (C) Igor Sysoev
 */


#include <ngx_config.h>
#include <ngx_core.h>
#include <ngx_event.h>


ngx_int_t ngx_event_mutex_timedlock(ngx_event_mutex_t *m, ngx_msec_t timer,
                                    ngx_event_t *ev)
{
    ngx_log_debug2(NGX_LOG_DEBUG_EVENT, ev->log, 0,
                   "lock event mutex %p lock:%XD", m, m->lock);

    if (m->lock) {

        if (m->events == NULL) {
            m->events = ev;

        } else {
            m->last->next = ev;
        }

        m->last = ev;
        ev->next = NULL;

#if (NGX_THREADS0)
        ev->light = 1;
#endif

        ngx_add_timer(ev, timer);

        return NGX_AGAIN;
    }

    m->lock = 1;

    return NGX_OK;
}


ngx_int_t ngx_event_mutex_unlock(ngx_event_mutex_t *m, ngx_log_t *log)
{
    ngx_event_t  *ev;

    if (m->lock == 0) {
        ngx_log_error(NGX_LOG_ALERT, log, 0,
                      "tring to unlock the free event mutex %p", m);
        return NGX_ERROR;
    }

    ngx_log_debug2(NGX_LOG_DEBUG_EVENT, log, 0,
                   "unlock event mutex %p, next event: %p", m, m->events);

    m->lock = 0;

    if (m->events) {
        ev = m->events;
        m->events = ev->next;

        ev->next = (ngx_event_t *) ngx_posted_events;
        ngx_posted_events = ev;
    }

    return NGX_OK;
}