src/replication.c

   1 #include "redis.h"
   2
   3 #include <sys/time.h>
   4 #include <unistd.h>
   5 #include <fcntl.h>
   6 #include <sys/stat.h>
   7
   8 /* ---------------------------------- MASTER -------------------------------- */
   9
  10 void replicationFeedSlaves(list *slaves, int dictid, robj **argv, int argc) {
  11     listNode *ln;
  12     listIter li;
  13     int j;
  14
  15     listRewind(slaves,&li);
  16     while((ln = listNext(&li))) {
  17         redisClient *slave = ln->value;
  18
  19         /* Don't feed slaves that are still waiting for BGSAVE to start */
  20         if (slave->replstate == REDIS_REPL_WAIT_BGSAVE_START) continue;
  21
  22         /* Feed slaves that are waiting for the initial SYNC (so these commands
  23          * are queued in the output buffer until the intial SYNC completes),
  24          * or are already in sync with the master. */
  25         if (slave->slaveseldb != dictid) {
  26             robj *selectcmd;
  27
  28             if (dictid >= 0 && dictid < REDIS_SHARED_SELECT_CMDS) {
  29                 selectcmd = shared.select[dictid];
  30                 incrRefCount(selectcmd);
  31             } else {
  32                 selectcmd = createObject(REDIS_STRING,
  33                     sdscatprintf(sdsempty(),"select %d\r\n",dictid));
  34             }
  35             addReply(slave,selectcmd);
  36             decrRefCount(selectcmd);
  37             slave->slaveseldb = dictid;
  38         }
  39         addReplyMultiBulkLen(slave,argc);
  40         for (j = 0; j < argc; j++) addReplyBulk(slave,argv[j]);
  41     }
  42 }
  43
  44 void replicationFeedMonitors(redisClient *c, list *monitors, int dictid, robj **argv, int argc) {
  45     listNode *ln;
  46     listIter li;
  47     int j, port;
  48     sds cmdrepr = sdsnew("+");
  49     robj *cmdobj;
  50     char ip[32];
  51     struct timeval tv;
  52
  53     gettimeofday(&tv,NULL);
  54     cmdrepr = sdscatprintf(cmdrepr,"%ld.%06ld ",(long)tv.tv_sec,(long)tv.tv_usec);
  55     if (c->flags & REDIS_LUA_CLIENT) {
  56         cmdrepr = sdscatprintf(cmdrepr,"[%d lua] ", dictid);
  57     } else {
  58         anetPeerToString(c->fd,ip,&port);
  59         cmdrepr = sdscatprintf(cmdrepr,"[%d %s:%d] ", dictid,ip,port);
  60     }
  61
  62     for (j = 0; j < argc; j++) {
  63         if (argv[j]->encoding == REDIS_ENCODING_INT) {
  64             cmdrepr = sdscatprintf(cmdrepr, "\"%ld\"", (long)argv[j]->ptr);
  65         } else {
  66             cmdrepr = sdscatrepr(cmdrepr,(char*)argv[j]->ptr,
  67                         sdslen(argv[j]->ptr));
  68         }
  69         if (j != argc-1)
  70             cmdrepr = sdscatlen(cmdrepr," ",1);
  71     }
  72     cmdrepr = sdscatlen(cmdrepr,"\r\n",2);
  73     cmdobj = createObject(REDIS_STRING,cmdrepr);
  74
  75     listRewind(monitors,&li);
  76     while((ln = listNext(&li))) {
  77         redisClient *monitor = ln->value;
  78         addReply(monitor,cmdobj);
  79     }
  80     decrRefCount(cmdobj);
  81 }
  82
  83 void syncCommand(redisClient *c) {
  84     /* ignore SYNC if aleady slave or in monitor mode */
  85     if (c->flags & REDIS_SLAVE) return;
  86
  87     /* Refuse SYNC requests if we are a slave but the link with our master
  88      * is not ok... */
  89     if (server.masterhost && server.repl_state != REDIS_REPL_CONNECTED) {
  90         addReplyError(c,"Can't SYNC while not connected with my master");
  91         return;
  92     }
  93
  94     /* SYNC can't be issued when the server has pending data to send to
  95      * the client about already issued commands. We need a fresh reply
  96      * buffer registering the differences between the BGSAVE and the current
  97      * dataset, so that we can copy to other slaves if needed. */
  98     if (listLength(c->reply) != 0) {
  99         addReplyError(c,"SYNC is invalid with pending input");
 100         return;
 101     }
 102
 103     redisLog(REDIS_NOTICE,"Slave ask for synchronization");
 104     /* Here we need to check if there is a background saving operation
 105      * in progress, or if it is required to start one */
 106     if (server.rdb_child_pid != -1) {
 107         /* Ok a background save is in progress. Let's check if it is a good
 108          * one for replication, i.e. if there is another slave that is
 109          * registering differences since the server forked to save */
 110         redisClient *slave;
 111         listNode *ln;
 112         listIter li;
 113
 114         listRewind(server.slaves,&li);
 115         while((ln = listNext(&li))) {
 116             slave = ln->value;
 117             if (slave->replstate == REDIS_REPL_WAIT_BGSAVE_END) break;
 118         }
 119         if (ln) {
 120             /* Perfect, the server is already registering differences for
 121              * another slave. Set the right state, and copy the buffer. */
 122             copyClientOutputBuffer(c,slave);
 123             c->replstate = REDIS_REPL_WAIT_BGSAVE_END;
 124             redisLog(REDIS_NOTICE,"Waiting for end of BGSAVE for SYNC");
 125         } else {
 126             /* No way, we need to wait for the next BGSAVE in order to
 127              * register differences */
 128             c->replstate = REDIS_REPL_WAIT_BGSAVE_START;
 129             redisLog(REDIS_NOTICE,"Waiting for next BGSAVE for SYNC");
 130         }
 131     } else {
 132         /* Ok we don't have a BGSAVE in progress, let's start one */
 133         redisLog(REDIS_NOTICE,"Starting BGSAVE for SYNC");
 134         if (rdbSaveBackground(server.rdb_filename) != REDIS_OK) {
 135             redisLog(REDIS_NOTICE,"Replication failed, can't BGSAVE");
 136             addReplyError(c,"Unable to perform background save");
 137             return;
 138         }
 139         c->replstate = REDIS_REPL_WAIT_BGSAVE_END;
 140     }
 141     c->repldbfd = -1;
 142     c->flags |= REDIS_SLAVE;
 143     c->slaveseldb = 0;
 144     listAddNodeTail(server.slaves,c);
 145     return;
 146 }
 147
 148 /* REPLCONF <option> <value> <option> <value> ...
 149  * This command is used by a slave in order to configure the replication
 150  * process before starting it with the SYNC command.
 151  *
 152  * Currently the only use of this command is to communicate to the master
 153  * what is the listening port of the Slave redis instance, so that the
 154  * master can accurately list slaves and their listening ports in
 155  * the INFO output.
 156  *
 157  * In the future the same command can be used in order to configure
 158  * the replication to initiate an incremental replication instead of a
 159  * full resync. */
 160 void replconfCommand(redisClient *c) {
 161     int j;
 162
 163     if ((c->argc % 2) == 0) {
 164         /* Number of arguments must be odd to make sure that every
 165          * option has a corresponding value. */
 166         addReply(c,shared.syntaxerr);
 167         return;
 168     }
 169
 170     /* Process every option-value pair. */
 171     for (j = 1; j < c->argc; j+=2) {
 172         if (!strcasecmp(c->argv[j]->ptr,"listening-port")) {
 173             long port;
 174
 175             if ((getLongFromObjectOrReply(c,c->argv[j+1],
 176                     &port,NULL) != REDIS_OK))
 177                 return;
 178             c->slave_listening_port = port;
 179         } else {
 180             addReplyErrorFormat(c,"Unrecognized REPLCONF option: %s",
 181                 (char*)c->argv[j]->ptr);
 182             return;
 183         }
 184     }
 185     addReply(c,shared.ok);
 186 }
 187
 188 void sendBulkToSlave(aeEventLoop *el, int fd, void *privdata, int mask) {
 189     redisClient *slave = privdata;
 190     REDIS_NOTUSED(el);
 191     REDIS_NOTUSED(mask);
 192     char buf[REDIS_IOBUF_LEN];
 193     ssize_t nwritten, buflen;
 194
 195     if (slave->repldboff == 0) {
 196         /* Write the bulk write count before to transfer the DB. In theory here
 197          * we don't know how much room there is in the output buffer of the
 198          * socket, but in pratice SO_SNDLOWAT (the minimum count for output
 199          * operations) will never be smaller than the few bytes we need. */
 200         sds bulkcount;
 201
 202         bulkcount = sdscatprintf(sdsempty(),"$%lld\r\n",(unsigned long long)
 203             slave->repldbsize);
 204         if (write(fd,bulkcount,sdslen(bulkcount)) != (signed)sdslen(bulkcount))
 205         {
 206             sdsfree(bulkcount);
 207             freeClient(slave);
 208             return;
 209         }
 210         sdsfree(bulkcount);
 211     }
 212     lseek(slave->repldbfd,slave->repldboff,SEEK_SET);
 213     buflen = read(slave->repldbfd,buf,REDIS_IOBUF_LEN);
 214     if (buflen <= 0) {
 215         redisLog(REDIS_WARNING,"Read error sending DB to slave: %s",
 216             (buflen == 0) ? "premature EOF" : strerror(errno));
 217         freeClient(slave);
 218         return;
 219     }
 220     if ((nwritten = write(fd,buf,buflen)) == -1) {
 221         redisLog(REDIS_VERBOSE,"Write error sending DB to slave: %s",
 222             strerror(errno));
 223         freeClient(slave);
 224         return;
 225     }
 226     slave->repldboff += nwritten;
 227     if (slave->repldboff == slave->repldbsize) {
 228         close(slave->repldbfd);
 229         slave->repldbfd = -1;
 230         aeDeleteFileEvent(server.el,slave->fd,AE_WRITABLE);
 231         slave->replstate = REDIS_REPL_ONLINE;
 232         if (aeCreateFileEvent(server.el, slave->fd, AE_WRITABLE,
 233             sendReplyToClient, slave) == AE_ERR) {
 234             freeClient(slave);
 235             return;
 236         }
 237         redisLog(REDIS_NOTICE,"Synchronization with slave succeeded");
 238     }
 239 }
 240
 241 /* This function is called at the end of every backgrond saving.
 242  * The argument bgsaveerr is REDIS_OK if the background saving succeeded
 243  * otherwise REDIS_ERR is passed to the function.
 244  *
 245  * The goal of this function is to handle slaves waiting for a successful
 246  * background saving in order to perform non-blocking synchronization. */
 247 void updateSlavesWaitingBgsave(int bgsaveerr) {
 248     listNode *ln;
 249     int startbgsave = 0;
 250     listIter li;
 251
 252     listRewind(server.slaves,&li);
 253     while((ln = listNext(&li))) {
 254         redisClient *slave = ln->value;
 255
 256         if (slave->replstate == REDIS_REPL_WAIT_BGSAVE_START) {
 257             startbgsave = 1;
 258             slave->replstate = REDIS_REPL_WAIT_BGSAVE_END;
 259         } else if (slave->replstate == REDIS_REPL_WAIT_BGSAVE_END) {
 260             struct redis_stat buf;
 261
 262             if (bgsaveerr != REDIS_OK) {
 263                 freeClient(slave);
 264                 redisLog(REDIS_WARNING,"SYNC failed. BGSAVE child returned an error");
 265                 continue;
 266             }
 267             if ((slave->repldbfd = open(server.rdb_filename,O_RDONLY)) == -1 ||
 268                 redis_fstat(slave->repldbfd,&buf) == -1) {
 269                 freeClient(slave);
 270                 redisLog(REDIS_WARNING,"SYNC failed. Can't open/stat DB after BGSAVE: %s", strerror(errno));
 271                 continue;
 272             }
 273             slave->repldboff = 0;
 274             slave->repldbsize = buf.st_size;
 275             slave->replstate = REDIS_REPL_SEND_BULK;
 276             aeDeleteFileEvent(server.el,slave->fd,AE_WRITABLE);
 277             if (aeCreateFileEvent(server.el, slave->fd, AE_WRITABLE, sendBulkToSlave, slave) == AE_ERR) {
 278                 freeClient(slave);
 279                 continue;
 280             }
 281         }
 282     }
 283     if (startbgsave) {
 284         if (rdbSaveBackground(server.rdb_filename) != REDIS_OK) {
 285             listIter li;
 286
 287             listRewind(server.slaves,&li);
 288             redisLog(REDIS_WARNING,"SYNC failed. BGSAVE failed");
 289             while((ln = listNext(&li))) {
 290                 redisClient *slave = ln->value;
 291
 292                 if (slave->replstate == REDIS_REPL_WAIT_BGSAVE_START)
 293                     freeClient(slave);
 294             }
 295         }
 296     }
 297 }
 298
 299 /* ----------------------------------- SLAVE -------------------------------- */
 300
 301 /* Abort the async download of the bulk dataset while SYNC-ing with master */
 302 void replicationAbortSyncTransfer(void) {
 303     redisAssert(server.repl_state == REDIS_REPL_TRANSFER);
 304
 305     aeDeleteFileEvent(server.el,server.repl_transfer_s,AE_READABLE);
 306     close(server.repl_transfer_s);
 307     close(server.repl_transfer_fd);
 308     unlink(server.repl_transfer_tmpfile);
 309     zfree(server.repl_transfer_tmpfile);
 310     server.repl_state = REDIS_REPL_CONNECT;
 311 }
 312
 313 /* Asynchronously read the SYNC payload we receive from a master */
 314 #define REPL_MAX_WRITTEN_BEFORE_FSYNC (1024*1024*8) /* 8 MB */
 315 void readSyncBulkPayload(aeEventLoop *el, int fd, void *privdata, int mask) {
 316     char buf[4096];
 317     ssize_t nread, readlen;
 318     off_t left;
 319     REDIS_NOTUSED(el);
 320     REDIS_NOTUSED(privdata);
 321     REDIS_NOTUSED(mask);
 322
 323     /* If repl_transfer_size == -1 we still have to read the bulk length
 324      * from the master reply. */
 325     if (server.repl_transfer_size == -1) {
 326         if (syncReadLine(fd,buf,1024,server.repl_syncio_timeout*1000) == -1) {
 327             redisLog(REDIS_WARNING,
 328                 "I/O error reading bulk count from MASTER: %s",
 329                 strerror(errno));
 330             goto error;
 331         }
 332
 333         if (buf[0] == '-') {
 334             redisLog(REDIS_WARNING,
 335                 "MASTER aborted replication with an error: %s",
 336                 buf+1);
 337             goto error;
 338         } else if (buf[0] == '\0') {
 339             /* At this stage just a newline works as a PING in order to take
 340              * the connection live. So we refresh our last interaction
 341              * timestamp. */
 342             server.repl_transfer_lastio = server.unixtime;
 343             return;
 344         } else if (buf[0] != '$') {
 345             redisLog(REDIS_WARNING,"Bad protocol from MASTER, the first byte is not '$', are you sure the host and port are right?");
 346             goto error;
 347         }
 348         server.repl_transfer_size = strtol(buf+1,NULL,10);
 349         redisLog(REDIS_NOTICE,
 350             "MASTER <-> SLAVE sync: receiving %ld bytes from master",
 351             server.repl_transfer_size);
 352         return;
 353     }
 354
 355     /* Read bulk data */
 356     left = server.repl_transfer_size - server.repl_transfer_read;
 357     readlen = (left < (signed)sizeof(buf)) ? left : (signed)sizeof(buf);
 358     nread = read(fd,buf,readlen);
 359     if (nread <= 0) {
 360         redisLog(REDIS_WARNING,"I/O error trying to sync with MASTER: %s",
 361             (nread == -1) ? strerror(errno) : "connection lost");
 362         replicationAbortSyncTransfer();
 363         return;
 364     }
 365     server.repl_transfer_lastio = server.unixtime;
 366     if (write(server.repl_transfer_fd,buf,nread) != nread) {
 367         redisLog(REDIS_WARNING,"Write error or short write writing to the DB dump file needed for MASTER <-> SLAVE synchronization: %s", strerror(errno));
 368         goto error;
 369     }
 370     server.repl_transfer_read += nread;
 371
 372     /* Sync data on disk from time to time, otherwise at the end of the transfer
 373      * we may suffer a big delay as the memory buffers are copied into the
 374      * actual disk. */
 375     if (server.repl_transfer_read >=
 376         server.repl_transfer_last_fsync_off + REPL_MAX_WRITTEN_BEFORE_FSYNC)
 377     {
 378         off_t sync_size = server.repl_transfer_read -
 379                           server.repl_transfer_last_fsync_off;
 380         rdb_fsync_range(server.repl_transfer_fd,
 381             server.repl_transfer_last_fsync_off, sync_size);
 382         server.repl_transfer_last_fsync_off += sync_size;
 383     }
 384
 385     /* Check if the transfer is now complete */
 386     if (server.repl_transfer_read == server.repl_transfer_size) {
 387         if (rename(server.repl_transfer_tmpfile,server.rdb_filename) == -1) {
 388             redisLog(REDIS_WARNING,"Failed trying to rename the temp DB into dump.rdb in MASTER <-> SLAVE synchronization: %s", strerror(errno));
 389             replicationAbortSyncTransfer();
 390             return;
 391         }
 392         redisLog(REDIS_NOTICE, "MASTER <-> SLAVE sync: Loading DB in memory");
 393         emptyDb();
 394         /* Before loading the DB into memory we need to delete the readable
 395          * handler, otherwise it will get called recursively since
 396          * rdbLoad() will call the event loop to process events from time to
 397          * time for non blocking loading. */
 398         aeDeleteFileEvent(server.el,server.repl_transfer_s,AE_READABLE);
 399         if (rdbLoad(server.rdb_filename) != REDIS_OK) {
 400             redisLog(REDIS_WARNING,"Failed trying to load the MASTER synchronization DB from disk");
 401             replicationAbortSyncTransfer();
 402             return;
 403         }
 404         /* Final setup of the connected slave <- master link */
 405         zfree(server.repl_transfer_tmpfile);
 406         close(server.repl_transfer_fd);
 407         server.master = createClient(server.repl_transfer_s);
 408         server.master->flags |= REDIS_MASTER;
 409         server.master->authenticated = 1;
 410         server.repl_state = REDIS_REPL_CONNECTED;
 411         redisLog(REDIS_NOTICE, "MASTER <-> SLAVE sync: Finished with success");
 412         /* Restart the AOF subsystem now that we finished the sync. This
 413          * will trigger an AOF rewrite, and when done will start appending
 414          * to the new file. */
 415         if (server.aof_state != REDIS_AOF_OFF) {
 416             int retry = 10;
 417
 418             stopAppendOnly();
 419             while (retry-- && startAppendOnly() == REDIS_ERR) {
 420                 redisLog(REDIS_WARNING,"Failed enabling the AOF after successful master synchrnization! Trying it again in one second.");
 421                 sleep(1);
 422             }
 423             if (!retry) {
 424                 redisLog(REDIS_WARNING,"FATAL: this slave instance finished the synchronization with its master, but the AOF can't be turned on. Exiting now.");
 425                 exit(1);
 426             }
 427         }
 428     }
 429
 430     return;
 431
 432 error:
 433     replicationAbortSyncTransfer();
 434     return;
 435 }
 436
 437 /* Send a synchronous command to the master. Used to send AUTH and
 438  * REPLCONF commands before starting the replication with SYNC.
 439  *
 440  * On success NULL is returned.
 441  * On error an sds string describing the error is returned.
 442  */
 443 char *sendSynchronousCommand(int fd, ...) {
 444     va_list ap;
 445     sds cmd = sdsempty();
 446     char *arg, buf[256];
 447
 448     /* Create the command to send to the master, we use simple inline
 449      * protocol for simplicity as currently we only send simple strings. */
 450     va_start(ap,fd);
 451     while(1) {
 452         arg = va_arg(ap, char*);
 453         if (arg == NULL) break;
 454
 455         if (sdslen(cmd) != 0) cmd = sdscatlen(cmd," ",1);
 456         cmd = sdscat(cmd,arg);
 457     }
 458     cmd = sdscatlen(cmd,"\r\n",2);
 459
 460     /* Transfer command to the server. */
 461     if (syncWrite(fd,cmd,sdslen(cmd),server.repl_syncio_timeout*1000) == -1) {
 462         sdsfree(cmd);
 463         return sdscatprintf(sdsempty(),"Writing to master: %s",
 464                 strerror(errno));
 465     }
 466     sdsfree(cmd);
 467
 468     /* Read the reply from the server. */
 469     if (syncReadLine(fd,buf,sizeof(buf),server.repl_syncio_timeout*1000) == -1)
 470     {
 471         return sdscatprintf(sdsempty(),"Reading from master: %s",
 472                 strerror(errno));
 473     }
 474
 475     /* Check for errors from the server. */
 476     if (buf[0] != '+') {
 477         return sdscatprintf(sdsempty(),"Error from master: %s", buf);
 478     }
 479
 480     return NULL; /* No errors. */
 481 }
 482
 483 void syncWithMaster(aeEventLoop *el, int fd, void *privdata, int mask) {
 484     char tmpfile[256], *err;
 485     int dfd, maxtries = 5;
 486     int sockerr = 0;
 487     socklen_t errlen = sizeof(sockerr);
 488     REDIS_NOTUSED(el);
 489     REDIS_NOTUSED(privdata);
 490     REDIS_NOTUSED(mask);
 491
 492     /* If this event fired after the user turned the instance into a master
 493      * with SLAVEOF NO ONE we must just return ASAP. */
 494     if (server.repl_state == REDIS_REPL_NONE) {
 495         close(fd);
 496         return;
 497     }
 498
 499     /* Check for errors in the socket. */
 500     if (getsockopt(fd, SOL_SOCKET, SO_ERROR, &sockerr, &errlen) == -1)
 501         sockerr = errno;
 502     if (sockerr) {
 503         aeDeleteFileEvent(server.el,fd,AE_READABLE|AE_WRITABLE);
 504         redisLog(REDIS_WARNING,"Error condition on socket for SYNC: %s",
 505             strerror(sockerr));
 506         goto error;
 507     }
 508
 509     /* If we were connecting, it's time to send a non blocking PING, we want to
 510      * make sure the master is able to reply before going into the actual
 511      * replication process where we have long timeouts in the order of
 512      * seconds (in the meantime the slave would block). */
 513     if (server.repl_state == REDIS_REPL_CONNECTING) {
 514         redisLog(REDIS_NOTICE,"Non blocking connect for SYNC fired the event.");
 515         /* Delete the writable event so that the readable event remains
 516          * registered and we can wait for the PONG reply. */
 517         aeDeleteFileEvent(server.el,fd,AE_WRITABLE);
 518         server.repl_state = REDIS_REPL_RECEIVE_PONG;
 519         /* Send the PING, don't check for errors at all, we have the timeout
 520          * that will take care about this. */
 521         syncWrite(fd,"PING\r\n",6,100);
 522         return;
 523     }
 524
 525     /* Receive the PONG command. */
 526     if (server.repl_state == REDIS_REPL_RECEIVE_PONG) {
 527         char buf[1024];
 528
 529         /* Delete the readable event, we no longer need it now that there is
 530          * the PING reply to read. */
 531         aeDeleteFileEvent(server.el,fd,AE_READABLE);
 532
 533         /* Read the reply with explicit timeout. */
 534         buf[0] = '\0';
 535         if (syncReadLine(fd,buf,sizeof(buf),
 536             server.repl_syncio_timeout*1000) == -1)
 537         {
 538             redisLog(REDIS_WARNING,
 539                 "I/O error reading PING reply from master: %s",
 540                 strerror(errno));
 541             goto error;
 542         }
 543
 544         /* We don't care about the reply, it can be +PONG or an error since
 545          * the server requires AUTH. As long as it replies correctly, it's
 546          * fine from our point of view. */
 547         if (buf[0] != '-' && buf[0] != '+') {
 548             redisLog(REDIS_WARNING,"Unexpected reply to PING from master.");
 549             goto error;
 550         } else {
 551             redisLog(REDIS_NOTICE,
 552                 "Master replied to PING, replication can continue...");
 553         }
 554     }
 555
 556     /* AUTH with the master if required. */
 557     if(server.masterauth) {
 558         err = sendSynchronousCommand(fd,"AUTH",server.masterauth,NULL);
 559         if (err) {
 560             redisLog(REDIS_WARNING,"Unable to AUTH to MASTER: %s",err);
 561             sdsfree(err);
 562             goto error;
 563         }
 564     }
 565
 566     /* Set the slave port, so that Master's INFO command can list the
 567      * slave listening port correctly. */
 568     {
 569         sds port = sdsfromlonglong(server.port);
 570         err = sendSynchronousCommand(fd,"REPLCONF","listening-port",port,
 571                                          NULL);
 572         sdsfree(port);
 573         /* Ignore the error if any, not all the Redis versions support
 574          * REPLCONF listening-port. */
 575         if (err) {
 576             redisLog(REDIS_NOTICE,"(non critical): Master does not understand REPLCONF listening-port: %s", err);
 577             sdsfree(err);
 578         }
 579     }
 580
 581     /* Issue the SYNC command */
 582     if (syncWrite(fd,"SYNC\r\n",6,server.repl_syncio_timeout*1000) == -1) {
 583         redisLog(REDIS_WARNING,"I/O error writing to MASTER: %s",
 584             strerror(errno));
 585         goto error;
 586     }
 587
 588     /* Prepare a suitable temp file for bulk transfer */
 589     while(maxtries--) {
 590         snprintf(tmpfile,256,
 591             "temp-%d.%ld.rdb",(int)server.unixtime,(long int)getpid());
 592         dfd = open(tmpfile,O_CREAT|O_WRONLY|O_EXCL,0644);
 593         if (dfd != -1) break;
 594         sleep(1);
 595     }
 596     if (dfd == -1) {
 597         redisLog(REDIS_WARNING,"Opening the temp file needed for MASTER <-> SLAVE synchronization: %s",strerror(errno));
 598         goto error;
 599     }
 600
 601     /* Setup the non blocking download of the bulk file. */
 602     if (aeCreateFileEvent(server.el,fd, AE_READABLE,readSyncBulkPayload,NULL)
 603             == AE_ERR)
 604     {
 605         redisLog(REDIS_WARNING,"Can't create readable event for SYNC");
 606         goto error;
 607     }
 608
 609     server.repl_state = REDIS_REPL_TRANSFER;
 610     server.repl_transfer_size = -1;
 611     server.repl_transfer_read = 0;
 612     server.repl_transfer_last_fsync_off = 0;
 613     server.repl_transfer_fd = dfd;
 614     server.repl_transfer_lastio = server.unixtime;
 615     server.repl_transfer_tmpfile = zstrdup(tmpfile);
 616     return;
 617
 618 error:
 619     close(fd);
 620     server.repl_transfer_s = -1;
 621     server.repl_state = REDIS_REPL_CONNECT;
 622     return;
 623 }
 624
 625 int connectWithMaster(void) {
 626     int fd;
 627
 628     fd = anetTcpNonBlockConnect(NULL,server.masterhost,server.masterport);
 629     if (fd == -1) {
 630         redisLog(REDIS_WARNING,"Unable to connect to MASTER: %s",
 631             strerror(errno));
 632         return REDIS_ERR;
 633     }
 634
 635     if (aeCreateFileEvent(server.el,fd,AE_READABLE|AE_WRITABLE,syncWithMaster,NULL) ==
 636             AE_ERR)
 637     {
 638         close(fd);
 639         redisLog(REDIS_WARNING,"Can't create readable event for SYNC");
 640         return REDIS_ERR;
 641     }
 642
 643     server.repl_transfer_lastio = server.unixtime;
 644     server.repl_transfer_s = fd;
 645     server.repl_state = REDIS_REPL_CONNECTING;
 646     return REDIS_OK;
 647 }
 648
 649 /* This function can be called when a non blocking connection is currently
 650  * in progress to undo it. */
 651 void undoConnectWithMaster(void) {
 652     int fd = server.repl_transfer_s;
 653
 654     redisAssert(server.repl_state == REDIS_REPL_CONNECTING ||
 655                 server.repl_state == REDIS_REPL_RECEIVE_PONG);
 656     aeDeleteFileEvent(server.el,fd,AE_READABLE|AE_WRITABLE);
 657     close(fd);
 658     server.repl_transfer_s = -1;
 659     server.repl_state = REDIS_REPL_CONNECT;
 660 }
 661
 662 void slaveofCommand(redisClient *c) {
 663     if (!strcasecmp(c->argv[1]->ptr,"no") &&
 664         !strcasecmp(c->argv[2]->ptr,"one")) {
 665         if (server.masterhost) {
 666             sdsfree(server.masterhost);
 667             server.masterhost = NULL;
 668             if (server.master) freeClient(server.master);
 669             if (server.repl_state == REDIS_REPL_TRANSFER)
 670                 replicationAbortSyncTransfer();
 671             else if (server.repl_state == REDIS_REPL_CONNECTING ||
 672                      server.repl_state == REDIS_REPL_RECEIVE_PONG)
 673                 undoConnectWithMaster();
 674             server.repl_state = REDIS_REPL_NONE;
 675             redisLog(REDIS_NOTICE,"MASTER MODE enabled (user request)");
 676         }
 677     } else {
 678         long port;
 679
 680         if ((getLongFromObjectOrReply(c, c->argv[2], &port, NULL) != REDIS_OK))
 681             return;
 682
 683         /* Check if we are already attached to the specified slave */
 684         if (server.masterhost && !strcasecmp(server.masterhost,c->argv[1]->ptr)
 685             && server.masterport == port) {
 686             redisLog(REDIS_NOTICE,"SLAVE OF would result into synchronization with the master we are already connected with. No operation performed.");
 687             addReplySds(c,sdsnew("+OK Already connected to specified master\r\n"));
 688             return;
 689         }
 690         /* There was no previous master or the user specified a different one,
 691          * we can continue. */
 692         sdsfree(server.masterhost);
 693         server.masterhost = sdsdup(c->argv[1]->ptr);
 694         server.masterport = port;
 695         if (server.master) freeClient(server.master);
 696         disconnectSlaves(); /* Force our slaves to resync with us as well. */
 697         if (server.repl_state == REDIS_REPL_TRANSFER)
 698             replicationAbortSyncTransfer();
 699         server.repl_state = REDIS_REPL_CONNECT;
 700         redisLog(REDIS_NOTICE,"SLAVE OF %s:%d enabled (user request)",
 701             server.masterhost, server.masterport);
 702     }
 703     addReply(c,shared.ok);
 704 }
 705
 706 /* --------------------------- REPLICATION CRON  ---------------------------- */
 707
 708 void replicationCron(void) {
 709     /* Non blocking connection timeout? */
 710     if (server.masterhost &&
 711         (server.repl_state == REDIS_REPL_CONNECTING ||
 712          server.repl_state == REDIS_REPL_RECEIVE_PONG) &&
 713         (time(NULL)-server.repl_transfer_lastio) > server.repl_timeout)
 714     {
 715         redisLog(REDIS_WARNING,"Timeout connecting to the MASTER...");
 716         undoConnectWithMaster();
 717     }
 718
 719     /* Bulk transfer I/O timeout? */
 720     if (server.masterhost && server.repl_state == REDIS_REPL_TRANSFER &&
 721         (time(NULL)-server.repl_transfer_lastio) > server.repl_timeout)
 722     {
 723         redisLog(REDIS_WARNING,"Timeout receiving bulk data from MASTER...");
 724         replicationAbortSyncTransfer();
 725     }
 726
 727     /* Timed out master when we are an already connected slave? */
 728     if (server.masterhost && server.repl_state == REDIS_REPL_CONNECTED &&
 729         (time(NULL)-server.master->lastinteraction) > server.repl_timeout)
 730     {
 731         redisLog(REDIS_WARNING,"MASTER time out: no data nor PING received...");
 732         freeClient(server.master);
 733     }
 734
 735     /* Check if we should connect to a MASTER */
 736     if (server.repl_state == REDIS_REPL_CONNECT) {
 737         redisLog(REDIS_NOTICE,"Connecting to MASTER...");
 738         if (connectWithMaster() == REDIS_OK) {
 739             redisLog(REDIS_NOTICE,"MASTER <-> SLAVE sync started");
 740         }
 741     }
 742
 743     /* If we have attached slaves, PING them from time to time.
 744      * So slaves can implement an explicit timeout to masters, and will
 745      * be able to detect a link disconnection even if the TCP connection
 746      * will not actually go down. */
 747     if (!(server.cronloops % (server.repl_ping_slave_period * REDIS_HZ))) {
 748         listIter li;
 749         listNode *ln;
 750
 751         listRewind(server.slaves,&li);
 752         while((ln = listNext(&li))) {
 753             redisClient *slave = ln->value;
 754
 755             /* Don't ping slaves that are in the middle of a bulk transfer
 756              * with the master for first synchronization. */
 757             if (slave->replstate == REDIS_REPL_SEND_BULK) continue;
 758             if (slave->replstate == REDIS_REPL_ONLINE) {
 759                 /* If the slave is online send a normal ping */
 760                 addReplySds(slave,sdsnew("*1\r\n$4\r\nPING\r\n"));
 761             } else {
 762                 /* Otherwise we are in the pre-synchronization stage.
 763                  * Just a newline will do the work of refreshing the
 764                  * connection last interaction time, and at the same time
 765                  * we'll be sure that being a single char there are no
 766                  * short-write problems. */
 767                 if (write(slave->fd, "\n", 1) == -1) {
 768                     /* Don't worry, it's just a ping. */
 769                 }
 770             }
 771         }
 772     }
 773 }