<section id="scheduler">
<title>Load balancer scheduler algorithm</title>
- <p>At present, there are 2 load balancer scheduler algorithms available
- for use: Request Counting and Weighted Traffic Counting. These are controlled
- via the <code>lbmethod</code> value of the Balancer definition. See
- the <directive module="mod_proxy">ProxyPass</directive> directive for
- more information.</p>
+ <p>At present, there are 3 load balancer scheduler algorithms available
+ for use: Request Counting, Weighted Traffic Counting and Pending Request
+ Counting. These are controlled via the <code>lbmethod</code> value of
+ the Balancer definition. See the <directive module="mod_proxy">ProxyPass</directive>
+ directive for more information.</p>
</section>
</section>
+<section id="busyness">
+
+ <title>Pending Request Counting Algorithm</title>
+
+ <p>Enabled via <code>lbmethod=bybusyness</code>, this scheduler keeps
+ track of how many requests each worker is assigned at present. A new
+ request is automatically assigned to the worker with the lowest
+ number of active requests. This is useful in the case of workers
+ that queue incoming requests independently of Apache, to ensure that
+ queue length stays even and a request is always given to the worker
+ most likely to service it fastest.</p>
+
+ <p>In the case of multiple least-busy workers, the statistics (and
+ weightings) used by the Request Counting method are used to break the
+ tie. Over time, the distribution of work will come to resemble that
+ characteristic of <code>byrequests</code>.</p>
+
+</section>
+
<section id="environment">
<title>Exported Environment Variables</title>
<p>At present there are 6 environment variables exported:</p>
}
#endif
}
+
return candidate;
+
}
static int rewrite_url(request_rec *r, proxy_worker *worker,
*worker = runtime;
}
+ (*worker)->s->busy++;
+
/* Add balancer/worker info to env. */
apr_table_setn(r->subprocess_env,
"BALANCER_NAME", (*balancer)->name);
#endif
+ if (worker && worker->s->busy)
+ worker->s->busy--;
+
return OK;
+
}
static void recalc_factors(proxy_balancer *balancer)
return mycandidate;
}
+static proxy_worker *find_best_bybusyness(proxy_balancer *balancer,
+ request_rec *r)
+{
+
+ int i;
+ proxy_worker *worker;
+ proxy_worker *mycandidate = NULL;
+ int cur_lbset = 0;
+ int max_lbset = 0;
+ int checking_standby;
+ int checked_standby;
+
+ int total_factor = 0;
+
+ ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server,
+ "proxy: Entering bybusyness for BALANCER (%s)",
+ balancer->name);
+
+ /* First try to see if we have available candidate */
+ do {
+
+ checking_standby = checked_standby = 0;
+ while (!mycandidate && !checked_standby) {
+
+ worker = (proxy_worker *)balancer->workers->elts;
+ for (i = 0; i < balancer->workers->nelts; i++, worker++) {
+ if (!checking_standby) { /* first time through */
+ if (worker->s->lbset > max_lbset)
+ max_lbset = worker->s->lbset;
+ }
+
+ if (worker->s->lbset > cur_lbset)
+ continue;
+
+ if ( (checking_standby ? !PROXY_WORKER_IS_STANDBY(worker) : PROXY_WORKER_IS_STANDBY(worker)) )
+ continue;
+
+ /* If the worker is in error state run
+ * retry on that worker. It will be marked as
+ * operational if the retry timeout is elapsed.
+ * The worker might still be unusable, but we try
+ * anyway.
+ */
+ if (!PROXY_WORKER_IS_USABLE(worker))
+ ap_proxy_retry_worker("BALANCER", worker, r->server);
+
+ /* Take into calculation only the workers that are
+ * not in error state or not disabled.
+ */
+ if (PROXY_WORKER_IS_USABLE(worker)) {
+
+ worker->s->lbstatus += worker->s->lbfactor;
+ total_factor += worker->s->lbfactor;
+
+ if (!mycandidate
+ || worker->s->busy < mycandidate->s->busy
+ || (worker->s->busy == mycandidate->s->busy && worker->s->lbstatus > mycandidate->s->lbstatus))
+ mycandidate = worker;
+
+ }
+
+ }
+
+ checked_standby = checking_standby++;
+
+ }
+
+ cur_lbset++;
+
+ } while (cur_lbset <= max_lbset && !mycandidate);
+
+ if (mycandidate) {
+
+ ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server,
+ "proxy: selected worker \"%s\" by busy factor %i (request lbstatus %i)",
+ mycandidate->name, mycandidate->s->busy, mycandidate->s->lbstatus);
+
+ mycandidate->s->lbstatus -= total_factor;
+
+ }
+
+ return mycandidate;
+
+}
+
/*
* How to add additional lbmethods:
* 1. Create func which determines "best" candidate worker
NULL
};
+static const proxy_balancer_method bybusyness =
+{
+ "bybusyness",
+ &find_best_bybusyness,
+ NULL
+};
+
+
static void ap_proxy_balancer_register_hook(apr_pool_t *p)
{
/* Only the mpm_winnt has child init hook handler.
proxy_hook_canon_handler(proxy_balancer_canon, NULL, NULL, APR_HOOK_FIRST);
ap_register_provider(p, PROXY_LBMETHOD, "bytraffic", "0", &bytraffic);
ap_register_provider(p, PROXY_LBMETHOD, "byrequests", "0", &byrequests);
+ ap_register_provider(p, PROXY_LBMETHOD, "bybusyness", "0", &bybusyness);
}
module AP_MODULE_DECLARE_DATA proxy_balancer_module = {
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