src/peer_sourcehash.cc

   1 /*
   2  * Copyright (C) 1996-2021 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 "PeerSelectState.h"
  17 #include "SquidConfig.h"
  18 #include "Store.h"
  19
  20 #include <cmath>
  21
  22 #define ROTATE_LEFT(x, n) (((x) << (n)) | ((x) >> (32-(n))))
  23
  24 static int n_sourcehash_peers = 0;
  25 static CachePeer **sourcehash_peers = NULL;
  26 static OBJH peerSourceHashCachemgr;
  27 static void peerSourceHashRegisterWithCacheManager(void);
  28
  29 static int
  30 peerSortWeight(const void *a, const void *b)
  31 {
  32     const CachePeer *const *p1 = (const CachePeer *const *)a;
  33     const CachePeer *const *p2 = (const CachePeer *const *)b;
  34     return (*p1)->weight - (*p2)->weight;
  35 }
  36
  37 void
  38 peerSourceHashInit(void)
  39 {
  40     int W = 0;
  41     int K;
  42     int k;
  43     double P_last, X_last, Xn;
  44     CachePeer *p;
  45     CachePeer **P;
  46     char *t;
  47     /* Clean up */
  48
  49     for (k = 0; k < n_sourcehash_peers; ++k) {
  50         cbdataReferenceDone(sourcehash_peers[k]);
  51     }
  52
  53     safe_free(sourcehash_peers);
  54     n_sourcehash_peers = 0;
  55     /* find out which peers we have */
  56
  57     for (p = Config.peers; p; p = p->next) {
  58         if (!p->options.sourcehash)
  59             continue;
  60
  61         assert(p->type == PEER_PARENT);
  62
  63         if (p->weight == 0)
  64             continue;
  65
  66         ++n_sourcehash_peers;
  67
  68         W += p->weight;
  69     }
  70
  71     peerSourceHashRegisterWithCacheManager();
  72
  73     if (n_sourcehash_peers == 0)
  74         return;
  75
  76     sourcehash_peers = (CachePeer **)xcalloc(n_sourcehash_peers, sizeof(*sourcehash_peers));
  77
  78     /* Build a list of the found peers and calculate hashes and load factors */
  79     for (P = sourcehash_peers, p = Config.peers; p; p = p->next) {
  80         if (!p->options.sourcehash)
  81             continue;
  82
  83         if (p->weight == 0)
  84             continue;
  85
  86         /* calculate this peers hash */
  87         p->sourcehash.hash = 0;
  88
  89         for (t = p->name; *t != 0; ++t)
  90             p->sourcehash.hash += ROTATE_LEFT(p->sourcehash.hash, 19) + (unsigned int) *t;
  91
  92         p->sourcehash.hash += p->sourcehash.hash * 0x62531965;
  93
  94         p->sourcehash.hash = ROTATE_LEFT(p->sourcehash.hash, 21);
  95
  96         /* and load factor */
  97         p->sourcehash.load_factor = ((double) p->weight) / (double) W;
  98
  99         if (floor(p->sourcehash.load_factor * 1000.0) == 0.0)
 100             p->sourcehash.load_factor = 0.0;
 101
 102         /* add it to our list of peers */
 103         *P++ = cbdataReference(p);
 104     }
 105
 106     /* Sort our list on weight */
 107     qsort(sourcehash_peers, n_sourcehash_peers, sizeof(*sourcehash_peers), peerSortWeight);
 108
 109     /* Calculate the load factor multipliers X_k
 110      *
 111      * X_1 = pow ((K*p_1), (1/K))
 112      * X_k = ([K-k+1] * [P_k - P_{k-1}])/(X_1 * X_2 * ... * X_{k-1})
 113      * X_k += pow ((X_{k-1}, {K-k+1})
 114      * X_k = pow (X_k, {1/(K-k+1)})
 115      * simplified to have X_1 part of the loop
 116      */
 117     K = n_sourcehash_peers;
 118
 119     P_last = 0.0;       /* Empty P_0 */
 120
 121     Xn = 1.0;           /* Empty starting point of X_1 * X_2 * ... * X_{x-1} */
 122
 123     X_last = 0.0;       /* Empty X_0, nullifies the first pow statement */
 124
 125     for (k = 1; k <= K; ++k) {
 126         double Kk1 = (double) (K - k + 1);
 127         p = sourcehash_peers[k - 1];
 128         p->sourcehash.load_multiplier = (Kk1 * (p->sourcehash.load_factor - P_last)) / Xn;
 129         p->sourcehash.load_multiplier += pow(X_last, Kk1);
 130         p->sourcehash.load_multiplier = pow(p->sourcehash.load_multiplier, 1.0 / Kk1);
 131         Xn *= p->sourcehash.load_multiplier;
 132         X_last = p->sourcehash.load_multiplier;
 133         P_last = p->sourcehash.load_factor;
 134     }
 135 }
 136
 137 static void
 138 peerSourceHashRegisterWithCacheManager(void)
 139 {
 140     Mgr::RegisterAction("sourcehash", "peer sourcehash information",
 141                         peerSourceHashCachemgr, 0, 1);
 142 }
 143
 144 CachePeer *
 145 peerSourceHashSelectParent(PeerSelector *ps)
 146 {
 147     int k;
 148     const char *c;
 149     CachePeer *p = NULL;
 150     CachePeer *tp;
 151     unsigned int user_hash = 0;
 152     unsigned int combined_hash;
 153     double score;
 154     double high_score = 0;
 155     const char *key = NULL;
 156     char ntoabuf[MAX_IPSTRLEN];
 157
 158     if (n_sourcehash_peers == 0)
 159         return NULL;
 160
 161     assert(ps);
 162     HttpRequest *request = ps->request;
 163
 164     key = request->client_addr.toStr(ntoabuf, sizeof(ntoabuf));
 165
 166     /* calculate hash key */
 167     debugs(39, 2, "peerSourceHashSelectParent: Calculating hash for " << key);
 168
 169     for (c = key; *c != 0; ++c)
 170         user_hash += ROTATE_LEFT(user_hash, 19) + *c;
 171
 172     /* select CachePeer */
 173     for (k = 0; k < n_sourcehash_peers; ++k) {
 174         tp = sourcehash_peers[k];
 175         combined_hash = (user_hash ^ tp->sourcehash.hash);
 176         combined_hash += combined_hash * 0x62531965;
 177         combined_hash = ROTATE_LEFT(combined_hash, 21);
 178         score = combined_hash * tp->sourcehash.load_multiplier;
 179         debugs(39, 3, "peerSourceHashSelectParent: " << tp->name << " combined_hash " << combined_hash  <<
 180                " score " << std::setprecision(0) << score);
 181
 182         if ((score > high_score) && peerHTTPOkay(tp, ps)) {
 183             p = tp;
 184             high_score = score;
 185         }
 186     }
 187
 188     if (p)
 189         debugs(39, 2, "peerSourceHashSelectParent: selected " << p->name);
 190
 191     return p;
 192 }
 193
 194 static void
 195 peerSourceHashCachemgr(StoreEntry * sentry)
 196 {
 197     CachePeer *p;
 198     int sumfetches = 0;
 199     storeAppendPrintf(sentry, "%24s %10s %10s %10s %10s\n",
 200                       "Hostname",
 201                       "Hash",
 202                       "Multiplier",
 203                       "Factor",
 204                       "Actual");
 205
 206     for (p = Config.peers; p; p = p->next)
 207         sumfetches += p->stats.fetches;
 208
 209     for (p = Config.peers; p; p = p->next) {
 210         storeAppendPrintf(sentry, "%24s %10x %10f %10f %10f\n",
 211                           p->name, p->sourcehash.hash,
 212                           p->sourcehash.load_multiplier,
 213                           p->sourcehash.load_factor,
 214                           sumfetches ? (double) p->stats.fetches / sumfetches : -1.0);
 215     }
 216 }
 217