src/peer_sourcehash.cc

   1 /*
   2  * Copyright (C) 1996-2017 The Squid Software Foundation and contributors
   3  *
   4  * Squid software is distributed under GPLv2+ license and includes
   5  * contributions from numerous individuals and organizations.
   6  * Please see the COPYING and CONTRIBUTORS files for details.
   7  */
   8
   9 /* DEBUG: section 39    Peer source hash based selection */
  10
  11 #include "squid.h"
  12 #include "CachePeer.h"
  13 #include "HttpRequest.h"
  14 #include "mgr/Registration.h"
  15 #include "neighbors.h"
  16 #include "SquidConfig.h"
  17 #include "Store.h"
  18
  19 #include <cmath>
  20
  21 #define ROTATE_LEFT(x, n) (((x) << (n)) | ((x) >> (32-(n))))
  22
  23 static int n_sourcehash_peers = 0;
  24 static CachePeer **sourcehash_peers = NULL;
  25 static OBJH peerSourceHashCachemgr;
  26 static void peerSourceHashRegisterWithCacheManager(void);
  27
  28 static int
  29 peerSortWeight(const void *a, const void *b)
  30 {
  31     const CachePeer *const *p1 = (const CachePeer *const *)a;
  32     const CachePeer *const *p2 = (const CachePeer *const *)b;
  33     return (*p1)->weight - (*p2)->weight;
  34 }
  35
  36 void
  37 peerSourceHashInit(void)
  38 {
  39     int W = 0;
  40     int K;
  41     int k;
  42     double P_last, X_last, Xn;
  43     CachePeer *p;
  44     CachePeer **P;
  45     char *t;
  46     /* Clean up */
  47
  48     for (k = 0; k < n_sourcehash_peers; ++k) {
  49         cbdataReferenceDone(sourcehash_peers[k]);
  50     }
  51
  52     safe_free(sourcehash_peers);
  53     n_sourcehash_peers = 0;
  54     /* find out which peers we have */
  55
  56     for (p = Config.peers; p; p = p->next) {
  57         if (!p->options.sourcehash)
  58             continue;
  59
  60         assert(p->type == PEER_PARENT);
  61
  62         if (p->weight == 0)
  63             continue;
  64
  65         ++n_sourcehash_peers;
  66
  67         W += p->weight;
  68     }
  69
  70     peerSourceHashRegisterWithCacheManager();
  71
  72     if (n_sourcehash_peers == 0)
  73         return;
  74
  75     sourcehash_peers = (CachePeer **)xcalloc(n_sourcehash_peers, sizeof(*sourcehash_peers));
  76
  77     /* Build a list of the found peers and calculate hashes and load factors */
  78     for (P = sourcehash_peers, p = Config.peers; p; p = p->next) {
  79         if (!p->options.sourcehash)
  80             continue;
  81
  82         if (p->weight == 0)
  83             continue;
  84
  85         /* calculate this peers hash */
  86         p->sourcehash.hash = 0;
  87
  88         for (t = p->name; *t != 0; ++t)
  89             p->sourcehash.hash += ROTATE_LEFT(p->sourcehash.hash, 19) + (unsigned int) *t;
  90
  91         p->sourcehash.hash += p->sourcehash.hash * 0x62531965;
  92
  93         p->sourcehash.hash = ROTATE_LEFT(p->sourcehash.hash, 21);
  94
  95         /* and load factor */
  96         p->sourcehash.load_factor = ((double) p->weight) / (double) W;
  97
  98         if (floor(p->sourcehash.load_factor * 1000.0) == 0.0)
  99             p->sourcehash.load_factor = 0.0;
 100
 101         /* add it to our list of peers */
 102         *P++ = cbdataReference(p);
 103     }
 104
 105     /* Sort our list on weight */
 106     qsort(sourcehash_peers, n_sourcehash_peers, sizeof(*sourcehash_peers), peerSortWeight);
 107
 108     /* Calculate the load factor multipliers X_k
 109      *
 110      * X_1 = pow ((K*p_1), (1/K))
 111      * X_k = ([K-k+1] * [P_k - P_{k-1}])/(X_1 * X_2 * ... * X_{k-1})
 112      * X_k += pow ((X_{k-1}, {K-k+1})
 113      * X_k = pow (X_k, {1/(K-k+1)})
 114      * simplified to have X_1 part of the loop
 115      */
 116     K = n_sourcehash_peers;
 117
 118     P_last = 0.0;       /* Empty P_0 */
 119
 120     Xn = 1.0;           /* Empty starting point of X_1 * X_2 * ... * X_{x-1} */
 121
 122     X_last = 0.0;       /* Empty X_0, nullifies the first pow statement */
 123
 124     for (k = 1; k <= K; ++k) {
 125         double Kk1 = (double) (K - k + 1);
 126         p = sourcehash_peers[k - 1];
 127         p->sourcehash.load_multiplier = (Kk1 * (p->sourcehash.load_factor - P_last)) / Xn;
 128         p->sourcehash.load_multiplier += pow(X_last, Kk1);
 129         p->sourcehash.load_multiplier = pow(p->sourcehash.load_multiplier, 1.0 / Kk1);
 130         Xn *= p->sourcehash.load_multiplier;
 131         X_last = p->sourcehash.load_multiplier;
 132         P_last = p->sourcehash.load_factor;
 133     }
 134 }
 135
 136 static void
 137 peerSourceHashRegisterWithCacheManager(void)
 138 {
 139     Mgr::RegisterAction("sourcehash", "peer sourcehash information",
 140                         peerSourceHashCachemgr, 0, 1);
 141 }
 142
 143 CachePeer *
 144 peerSourceHashSelectParent(HttpRequest * request)
 145 {
 146     int k;
 147     const char *c;
 148     CachePeer *p = NULL;
 149     CachePeer *tp;
 150     unsigned int user_hash = 0;
 151     unsigned int combined_hash;
 152     double score;
 153     double high_score = 0;
 154     const char *key = NULL;
 155     char ntoabuf[MAX_IPSTRLEN];
 156
 157     if (n_sourcehash_peers == 0)
 158         return NULL;
 159
 160     key = request->client_addr.toStr(ntoabuf, sizeof(ntoabuf));
 161
 162     /* calculate hash key */
 163     debugs(39, 2, "peerSourceHashSelectParent: Calculating hash for " << key);
 164
 165     for (c = key; *c != 0; ++c)
 166         user_hash += ROTATE_LEFT(user_hash, 19) + *c;
 167
 168     /* select CachePeer */
 169     for (k = 0; k < n_sourcehash_peers; ++k) {
 170         tp = sourcehash_peers[k];
 171         combined_hash = (user_hash ^ tp->sourcehash.hash);
 172         combined_hash += combined_hash * 0x62531965;
 173         combined_hash = ROTATE_LEFT(combined_hash, 21);
 174         score = combined_hash * tp->sourcehash.load_multiplier;
 175         debugs(39, 3, "peerSourceHashSelectParent: " << tp->name << " combined_hash " << combined_hash  <<
 176                " score " << std::setprecision(0) << score);
 177
 178         if ((score > high_score) && peerHTTPOkay(tp, request)) {
 179             p = tp;
 180             high_score = score;
 181         }
 182     }
 183
 184     if (p)
 185         debugs(39, 2, "peerSourceHashSelectParent: selected " << p->name);
 186
 187     return p;
 188 }
 189
 190 static void
 191 peerSourceHashCachemgr(StoreEntry * sentry)
 192 {
 193     CachePeer *p;
 194     int sumfetches = 0;
 195     storeAppendPrintf(sentry, "%24s %10s %10s %10s %10s\n",
 196                       "Hostname",
 197                       "Hash",
 198                       "Multiplier",
 199                       "Factor",
 200                       "Actual");
 201
 202     for (p = Config.peers; p; p = p->next)
 203         sumfetches += p->stats.fetches;
 204
 205     for (p = Config.peers; p; p = p->next) {
 206         storeAppendPrintf(sentry, "%24s %10x %10f %10f %10f\n",
 207                           p->name, p->sourcehash.hash,
 208                           p->sourcehash.load_multiplier,
 209                           p->sourcehash.load_factor,
 210                           sumfetches ? (double) p->stats.fetches / sumfetches : -1.0);
 211     }
 212 }
 213