Add in independent byrequests lbmethod

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@722949 13f79535-47bb-0310-9956-ffa450edef68

1 files changed, 165 insertions, 0 deletions

diff --git a/modules/proxy/balancers/mod_lbmethod_byrequests.c b/modules/proxy/balancers/mod_lbmethod_byrequests.c
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+++ b/modules/proxy/balancers/mod_lbmethod_byrequests.c
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+/* Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "mod_proxy.h"
+#include "scoreboard.h"
+#include "ap_mpm.h"
+#include "apr_version.h"
+#include "apr_hooks.h"
+
+module AP_MODULE_DECLARE_DATA lbmethod_byrequests_module;
+
+/*
+ * The idea behind the find_best_byrequests scheduler is the following:
+ *
+ * lbfactor is "how much we expect this worker to work", or "the worker's
+ * normalized work quota".
+ *
+ * lbstatus is "how urgent this worker has to work to fulfill its quota
+ * of work".
+ *
+ * We distribute each worker's work quota to the worker, and then look
+ * which of them needs to work most urgently (biggest lbstatus).  This
+ * worker is then selected for work, and its lbstatus reduced by the
+ * total work quota we distributed to all workers.  Thus the sum of all
+ * lbstatus does not change.(*)
+ *
+ * If some workers are disabled, the others will
+ * still be scheduled correctly.
+ *
+ * If a balancer is configured as follows:
+ *
+ * worker     a    b    c    d
+ * lbfactor  25   25   25   25
+ *
+ * And b gets disabled, the following schedule is produced:
+ *
+ *    a c d a c d a c d ...
+ *
+ * Note that the above lbfactor setting is the *exact* same as:
+ *
+ * worker     a    b    c    d
+ * lbfactor   1    1    1    1
+ *
+ * Asymmetric configurations work as one would expect. For
+ * example:
+ *
+ * worker     a    b    c    d
+ * lbfactor   1    1    1    2
+ *
+ * would have a, b and c all handling about the same
+ * amount of load with d handling twice what a or b
+ * or c handles individually. So we could see:
+ *
+ *   b a d c d a c d b d ...
+ *
+ */
+
+static proxy_worker *find_best_byrequests(proxy_balancer *balancer,
+                                request_rec *r)
+{
+    int i;
+    int total_factor = 0;
+    proxy_worker *worker;
+    proxy_worker *mycandidate = NULL;
+    int cur_lbset = 0;
+    int max_lbset = 0;
+    int checking_standby;
+    int checked_standby;
+    
+    ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server,
+                 "proxy: Entering byrequests 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->lbstatus > mycandidate->s->lbstatus)
+                        mycandidate = worker;
+                }
+            }
+            checked_standby = checking_standby++;
+        }
+        cur_lbset++;
+    } while (cur_lbset <= max_lbset && !mycandidate);
+
+    if (mycandidate) {
+        mycandidate->s->lbstatus -= total_factor;
+        ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server,
+                     "proxy: byrequests selected worker \"%s\" : busy %" APR_SIZE_T_FMT " : lbstatus %d",
+                     mycandidate->name, mycandidate->s->busy, mycandidate->s->lbstatus);
+
+    }
+
+    return mycandidate;
+}
+
+/*
+ * How to add additional lbmethods:
+ *   1. Create func which determines "best" candidate worker
+ *      (eg: find_best_bytraffic, above)
+ *   2. Register it as a provider.
+ */
+static const proxy_balancer_method byrequests =
+{
+    "byrequests",
+    &find_best_byrequests,
+    NULL
+};
+
+static void register_hook(apr_pool_t *p)
+{
+    /* Only the mpm_winnt has child init hook handler.
+     * make sure that we are called after the mpm
+     * initializes and after the mod_proxy
+     */
+    ap_register_provider(p, PROXY_LBMETHOD, "byrequests", "0", &byrequests);
+}
+
+module AP_MODULE_DECLARE_DATA lbmethod_byrequests_module = {
+    STANDARD20_MODULE_STUFF,
+    NULL,       /* create per-directory config structure */
+    NULL,       /* merge per-directory config structures */
+    NULL,       /* create per-server config structure */
+    NULL,       /* merge per-server config structures */
+    NULL,       /* command apr_table_t */
+    register_hook /* register hooks */
+};