modules/proxy/balancers/mod_lbmethod_bytraffic.c

   1 /* Licensed to the Apache Software Foundation (ASF) under one or more
   2  * contributor license agreements.  See the NOTICE file distributed with
   3  * this work for additional information regarding copyright ownership.
   4  * The ASF licenses this file to You under the Apache License, Version 2.0
   5  * (the "License"); you may not use this file except in compliance with
   6  * the License.  You may obtain a copy of the License at
   7  *
   8  *     http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16
  17 #include "mod_proxy.h"
  18 #include "scoreboard.h"
  19 #include "ap_mpm.h"
  20 #include "apr_version.h"
  21 #include "apr_hooks.h"
  22
  23 module AP_MODULE_DECLARE_DATA lbmethod_bytraffic_module;
  24
  25 /*
  26  * The idea behind the find_best_bytraffic scheduler is the following:
  27  *
  28  * We know the amount of traffic (bytes in and out) handled by each
  29  * worker. We normalize that traffic by each workers' weight. So assuming
  30  * a setup as below:
  31  *
  32  * worker     a    b    c
  33  * lbfactor   1    1    3
  34  *
  35  * the scheduler will allow worker c to handle 3 times the
  36  * traffic of a and b. If each request/response results in the
  37  * same amount of traffic, then c would be accessed 3 times as
  38  * often as a or b. If, for example, a handled a request that
  39  * resulted in a large i/o bytecount, then b and c would be
  40  * chosen more often, to even things out.
  41  */
  42 static proxy_worker *find_best_bytraffic(proxy_balancer *balancer,
  43                                          request_rec *r)
  44 {
  45     int i;
  46     apr_off_t mytraffic = 0;
  47     apr_off_t curmin = 0;
  48     proxy_worker *worker;
  49     proxy_worker *mycandidate = NULL;
  50     int cur_lbset = 0;
  51     int max_lbset = 0;
  52     int checking_standby;
  53     int checked_standby;
  54
  55     ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server,
  56                  "proxy: Entering bytraffic for BALANCER (%s)",
  57                  balancer->name);
  58
  59     /* First try to see if we have available candidate */
  60     do {
  61         checking_standby = checked_standby = 0;
  62         while (!mycandidate && !checked_standby) {
  63             worker = (proxy_worker *)balancer->workers->elts;
  64             for (i = 0; i < balancer->workers->nelts; i++, worker++) {
  65                 if (!checking_standby) {    /* first time through */
  66                     if (worker->s->lbset > max_lbset)
  67                         max_lbset = worker->s->lbset;
  68                 }
  69                 if (worker->s->lbset != cur_lbset)
  70                     continue;
  71                 if ( (checking_standby ? !PROXY_WORKER_IS_STANDBY(worker) : PROXY_WORKER_IS_STANDBY(worker)) )
  72                     continue;
  73                 /* If the worker is in error state run
  74                  * retry on that worker. It will be marked as
  75                  * operational if the retry timeout is elapsed.
  76                  * The worker might still be unusable, but we try
  77                  * anyway.
  78                  */
  79                 if (!PROXY_WORKER_IS_USABLE(worker))
  80                     ap_proxy_retry_worker("BALANCER", worker, r->server);
  81                 /* Take into calculation only the workers that are
  82                  * not in error state or not disabled.
  83                  */
  84                 if (PROXY_WORKER_IS_USABLE(worker)) {
  85                     mytraffic = (worker->s->transferred/worker->s->lbfactor) +
  86                                 (worker->s->read/worker->s->lbfactor);
  87                     if (!mycandidate || mytraffic < curmin) {
  88                         mycandidate = worker;
  89                         curmin = mytraffic;
  90                     }
  91                 }
  92             }
  93             checked_standby = checking_standby++;
  94         }
  95         cur_lbset++;
  96     } while (cur_lbset <= max_lbset && !mycandidate);
  97
  98     if (mycandidate) {
  99         ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server,
 100                      "proxy: bytraffic selected worker \"%s\" : busy %" APR_SIZE_T_FMT,
 101                      mycandidate->name, mycandidate->s->busy);
 102
 103     }
 104
 105     return mycandidate;
 106 }
 107
 108 static const proxy_balancer_method bytraffic =
 109 {
 110     "bytraffic",
 111     &find_best_bytraffic,
 112     NULL
 113 };
 114
 115 static void register_hook(apr_pool_t *p)
 116 {
 117     /* Only the mpm_winnt has child init hook handler.
 118      * make sure that we are called after the mpm
 119      * initializes and after the mod_proxy
 120      */
 121     ap_register_provider(p, PROXY_LBMETHOD, "bytraffic", "0", &bytraffic);
 122 }
 123
 124 module AP_MODULE_DECLARE_DATA lbmethod_bytraffic_module = {
 125     STANDARD20_MODULE_STUFF,
 126     NULL,       /* create per-directory config structure */
 127     NULL,       /* merge per-directory config structures */
 128     NULL,       /* create per-server config structure */
 129     NULL,       /* merge per-server config structures */
 130     NULL,       /* command apr_table_t */
 131     register_hook /* register hooks */
 132 };