granicus.if.org Git - postgresql/blob - src/backend/replication/walsender.c

   1 /*-------------------------------------------------------------------------
   2  *
   3  * walsender.c
   4  *
   5  * The WAL sender process (walsender) is new as of Postgres 9.0. It takes
   6  * care of sending XLOG from the primary server to a single recipient.
   7  * (Note that there can be more than one walsender process concurrently.)
   8  * It is started by the postmaster when the walreceiver of a standby server
   9  * connects to the primary server and requests XLOG streaming replication.
  10  * It attempts to keep reading XLOG records from the disk and sending them
  11  * to the standby server, as long as the connection is alive (i.e., like
  12  * any backend, there is a one-to-one relationship between a connection
  13  * and a walsender process).
  14  *
  15  * Normal termination is by SIGTERM, which instructs the walsender to
  16  * close the connection and exit(0) at next convenient moment. Emergency
  17  * termination is by SIGQUIT; like any backend, the walsender will simply
  18  * abort and exit on SIGQUIT. A close of the connection and a FATAL error
  19  * are treated as not a crash but approximately normal termination;
  20  * the walsender will exit quickly without sending any more XLOG records.
  21  *
  22  * If the server is shut down, postmaster sends us SIGUSR2 after all
  23  * regular backends have exited and the shutdown checkpoint has been written.
  24  * This instruct walsender to send any outstanding WAL, including the
  25  * shutdown checkpoint record, and then exit.
  26  *
  27  *
  28  * Portions Copyright (c) 2010-2010, PostgreSQL Global Development Group
  29  *
  30  * IDENTIFICATION
  31  *        $PostgreSQL: pgsql/src/backend/replication/walsender.c,v 1.29 2010/07/22 13:03:11 rhaas Exp $
  32  *
  33  *-------------------------------------------------------------------------
  34  */
  35 #include "postgres.h"
  36
  37 #include <unistd.h>
  38
  39 #include "access/xlog_internal.h"
  40 #include "catalog/pg_type.h"
  41 #include "libpq/libpq.h"
  42 #include "libpq/pqformat.h"
  43 #include "libpq/pqsignal.h"
  44 #include "miscadmin.h"
  45 #include "replication/walprotocol.h"
  46 #include "replication/walsender.h"
  47 #include "storage/fd.h"
  48 #include "storage/ipc.h"
  49 #include "storage/pmsignal.h"
  50 #include "tcop/tcopprot.h"
  51 #include "utils/guc.h"
  52 #include "utils/memutils.h"
  53 #include "utils/ps_status.h"
  54
  55
  56 /* Array of WalSnds in shared memory */
  57 WalSndCtlData *WalSndCtl = NULL;
  58
  59 /* My slot in the shared memory array */
  60 static WalSnd *MyWalSnd = NULL;
  61
  62 /* Global state */
  63 bool            am_walsender = false;           /* Am I a walsender process ? */
  64
  65 /* User-settable parameters for walsender */
  66 int                     max_wal_senders = 0;    /* the maximum number of concurrent walsenders */
  67 int                     WalSndDelay = 200;      /* max sleep time between some actions */
  68
  69 #define NAPTIME_PER_CYCLE 100000L               /* max sleep time between cycles
  70                                                                                  * (100ms) */
  71
  72 /*
  73  * These variables are used similarly to openLogFile/Id/Seg/Off,
  74  * but for walsender to read the XLOG.
  75  */
  76 static int      sendFile = -1;
  77 static uint32 sendId = 0;
  78 static uint32 sendSeg = 0;
  79 static uint32 sendOff = 0;
  80
  81 /*
  82  * How far have we sent WAL already? This is also advertised in
  83  * MyWalSnd->sentPtr.  (Actually, this is the next WAL location to send.)
  84  */
  85 static XLogRecPtr sentPtr = {0, 0};
  86
  87 /* Flags set by signal handlers for later service in main loop */
  88 static volatile sig_atomic_t got_SIGHUP = false;
  89 static volatile sig_atomic_t shutdown_requested = false;
  90 static volatile sig_atomic_t ready_to_stop = false;
  91
  92 /* Signal handlers */
  93 static void WalSndSigHupHandler(SIGNAL_ARGS);
  94 static void WalSndShutdownHandler(SIGNAL_ARGS);
  95 static void WalSndQuickDieHandler(SIGNAL_ARGS);
  96 static void WalSndLastCycleHandler(SIGNAL_ARGS);
  97
  98 /* Prototypes for private functions */
  99 static int      WalSndLoop(void);
 100 static void InitWalSnd(void);
 101 static void WalSndHandshake(void);
 102 static void WalSndKill(int code, Datum arg);
 103 static void XLogRead(char *buf, XLogRecPtr recptr, Size nbytes);
 104 static bool XLogSend(char *msgbuf, bool *caughtup);
 105 static void CheckClosedConnection(void);
 106
 107
 108 /* Main entry point for walsender process */
 109 int
 110 WalSenderMain(void)
 111 {
 112         MemoryContext walsnd_context;
 113
 114         if (RecoveryInProgress())
 115                 ereport(FATAL,
 116                                 (errcode(ERRCODE_CANNOT_CONNECT_NOW),
 117                                  errmsg("recovery is still in progress, can't accept WAL streaming connections")));
 118
 119         /* Create a per-walsender data structure in shared memory */
 120         InitWalSnd();
 121
 122         /*
 123          * Create a memory context that we will do all our work in.  We do this so
 124          * that we can reset the context during error recovery and thereby avoid
 125          * possible memory leaks.  Formerly this code just ran in
 126          * TopMemoryContext, but resetting that would be a really bad idea.
 127          *
 128          * XXX: we don't actually attempt error recovery in walsender, we just
 129          * close the connection and exit.
 130          */
 131         walsnd_context = AllocSetContextCreate(TopMemoryContext,
 132                                                                                    "Wal Sender",
 133                                                                                    ALLOCSET_DEFAULT_MINSIZE,
 134                                                                                    ALLOCSET_DEFAULT_INITSIZE,
 135                                                                                    ALLOCSET_DEFAULT_MAXSIZE);
 136         MemoryContextSwitchTo(walsnd_context);
 137
 138         /* Unblock signals (they were blocked when the postmaster forked us) */
 139         PG_SETMASK(&UnBlockSig);
 140
 141         /* Tell the standby that walsender is ready for receiving commands */
 142         ReadyForQuery(DestRemote);
 143
 144         /* Handle handshake messages before streaming */
 145         WalSndHandshake();
 146
 147         /* Main loop of walsender */
 148         return WalSndLoop();
 149 }
 150
 151 /*
 152  * Execute commands from walreceiver, until we enter streaming mode.
 153  */
 154 static void
 155 WalSndHandshake(void)
 156 {
 157         StringInfoData input_message;
 158         bool            replication_started = false;
 159
 160         initStringInfo(&input_message);
 161
 162         while (!replication_started)
 163         {
 164                 int                     firstchar;
 165
 166                 /* Wait for a command to arrive */
 167                 firstchar = pq_getbyte();
 168
 169                 /*
 170                  * Emergency bailout if postmaster has died.  This is to avoid the
 171                  * necessity for manual cleanup of all postmaster children.
 172                  */
 173                 if (!PostmasterIsAlive(true))
 174                         exit(1);
 175
 176                 /*
 177                  * Check for any other interesting events that happened while we
 178                  * slept.
 179                  */
 180                 if (got_SIGHUP)
 181                 {
 182                         got_SIGHUP = false;
 183                         ProcessConfigFile(PGC_SIGHUP);
 184                 }
 185
 186                 if (firstchar != EOF)
 187                 {
 188                         /*
 189                          * Read the message contents. This is expected to be done without
 190                          * blocking because we've been able to get message type code.
 191                          */
 192                         if (pq_getmessage(&input_message, 0))
 193                                 firstchar = EOF;        /* suitable message already logged */
 194                 }
 195
 196                 /* Handle the very limited subset of commands expected in this phase */
 197                 switch (firstchar)
 198                 {
 199                         case 'Q':                       /* Query message */
 200                                 {
 201                                         const char *query_string;
 202                                         XLogRecPtr      recptr;
 203
 204                                         query_string = pq_getmsgstring(&input_message);
 205                                         pq_getmsgend(&input_message);
 206
 207                                         if (strcmp(query_string, "IDENTIFY_SYSTEM") == 0)
 208                                         {
 209                                                 StringInfoData buf;
 210                                                 char            sysid[32];
 211                                                 char            tli[11];
 212
 213                                                 /*
 214                                                  * Reply with a result set with one row, two columns.
 215                                                  * First col is system ID, and second is timeline ID
 216                                                  */
 217
 218                                                 snprintf(sysid, sizeof(sysid), UINT64_FORMAT,
 219                                                                  GetSystemIdentifier());
 220                                                 snprintf(tli, sizeof(tli), "%u", ThisTimeLineID);
 221
 222                                                 /* Send a RowDescription message */
 223                                                 pq_beginmessage(&buf, 'T');
 224                                                 pq_sendint(&buf, 2, 2); /* 2 fields */
 225
 226                                                 /* first field */
 227                                                 pq_sendstring(&buf, "systemid");                /* col name */
 228                                                 pq_sendint(&buf, 0, 4); /* table oid */
 229                                                 pq_sendint(&buf, 0, 2); /* attnum */
 230                                                 pq_sendint(&buf, TEXTOID, 4);   /* type oid */
 231                                                 pq_sendint(&buf, -1, 2);                /* typlen */
 232                                                 pq_sendint(&buf, 0, 4); /* typmod */
 233                                                 pq_sendint(&buf, 0, 2); /* format code */
 234
 235                                                 /* second field */
 236                                                 pq_sendstring(&buf, "timeline");                /* col name */
 237                                                 pq_sendint(&buf, 0, 4); /* table oid */
 238                                                 pq_sendint(&buf, 0, 2); /* attnum */
 239                                                 pq_sendint(&buf, INT4OID, 4);   /* type oid */
 240                                                 pq_sendint(&buf, 4, 2); /* typlen */
 241                                                 pq_sendint(&buf, 0, 4); /* typmod */
 242                                                 pq_sendint(&buf, 0, 2); /* format code */
 243                                                 pq_endmessage(&buf);
 244
 245                                                 /* Send a DataRow message */
 246                                                 pq_beginmessage(&buf, 'D');
 247                                                 pq_sendint(&buf, 2, 2); /* # of columns */
 248                                                 pq_sendint(&buf, strlen(sysid), 4);             /* col1 len */
 249                                                 pq_sendbytes(&buf, (char *) &sysid, strlen(sysid));
 250                                                 pq_sendint(&buf, strlen(tli), 4);               /* col2 len */
 251                                                 pq_sendbytes(&buf, (char *) tli, strlen(tli));
 252                                                 pq_endmessage(&buf);
 253
 254                                                 /* Send CommandComplete and ReadyForQuery messages */
 255                                                 EndCommand("SELECT", DestRemote);
 256                                                 ReadyForQuery(DestRemote);
 257                                                 /* ReadyForQuery did pq_flush for us */
 258                                         }
 259                                         else if (sscanf(query_string, "START_REPLICATION %X/%X",
 260                                                                         &recptr.xlogid, &recptr.xrecoff) == 2)
 261                                         {
 262                                                 StringInfoData buf;
 263
 264                                                 /*
 265                                                  * Check that we're logging enough information in the
 266                                                  * WAL for log-shipping.
 267                                                  *
 268                                                  * NOTE: This only checks the current value of
 269                                                  * wal_level. Even if the current setting is not
 270                                                  * 'minimal', there can be old WAL in the pg_xlog
 271                                                  * directory that was created with 'minimal'. So this
 272                                                  * is not bulletproof, the purpose is just to give a
 273                                                  * user-friendly error message that hints how to
 274                                                  * configure the system correctly.
 275                                                  */
 276                                                 if (wal_level == WAL_LEVEL_MINIMAL)
 277                                                         ereport(FATAL,
 278                                                                         (errcode(ERRCODE_CANNOT_CONNECT_NOW),
 279                                                                          errmsg("standby connections not allowed because wal_level=minimal")));
 280
 281                                                 /* Send a CopyOutResponse message, and start streaming */
 282                                                 pq_beginmessage(&buf, 'H');
 283                                                 pq_sendbyte(&buf, 0);
 284                                                 pq_sendint(&buf, 0, 2);
 285                                                 pq_endmessage(&buf);
 286                                                 pq_flush();
 287
 288                                                 /*
 289                                                  * Initialize position to the received one, then the
 290                                                  * xlog records begin to be shipped from that position
 291                                                  */
 292                                                 sentPtr = recptr;
 293
 294                                                 /* break out of the loop */
 295                                                 replication_started = true;
 296                                         }
 297                                         else
 298                                         {
 299                                                 ereport(FATAL,
 300                                                                 (errcode(ERRCODE_PROTOCOL_VIOLATION),
 301                                                                  errmsg("invalid standby query string: %s", query_string)));
 302                                         }
 303                                         break;
 304                                 }
 305
 306                         case 'X':
 307                                 /* standby is closing the connection */
 308                                 proc_exit(0);
 309
 310                         case EOF:
 311                                 /* standby disconnected unexpectedly */
 312                                 ereport(COMMERROR,
 313                                                 (errcode(ERRCODE_PROTOCOL_VIOLATION),
 314                                                  errmsg("unexpected EOF on standby connection")));
 315                                 proc_exit(0);
 316
 317                         default:
 318                                 ereport(FATAL,
 319                                                 (errcode(ERRCODE_PROTOCOL_VIOLATION),
 320                                                  errmsg("invalid standby handshake message type %d", firstchar)));
 321                 }
 322         }
 323 }
 324
 325 /*
 326  * Check if the remote end has closed the connection.
 327  */
 328 static void
 329 CheckClosedConnection(void)
 330 {
 331         unsigned char firstchar;
 332         int                     r;
 333
 334         r = pq_getbyte_if_available(&firstchar);
 335         if (r < 0)
 336         {
 337                 /* unexpected error or EOF */
 338                 ereport(COMMERROR,
 339                                 (errcode(ERRCODE_PROTOCOL_VIOLATION),
 340                                  errmsg("unexpected EOF on standby connection")));
 341                 proc_exit(0);
 342         }
 343         if (r == 0)
 344         {
 345                 /* no data available without blocking */
 346                 return;
 347         }
 348
 349         /* Handle the very limited subset of commands expected in this phase */
 350         switch (firstchar)
 351         {
 352                         /*
 353                          * 'X' means that the standby is closing down the socket.
 354                          */
 355                 case 'X':
 356                         proc_exit(0);
 357
 358                 default:
 359                         ereport(FATAL,
 360                                         (errcode(ERRCODE_PROTOCOL_VIOLATION),
 361                                          errmsg("invalid standby closing message type %d",
 362                                                         firstchar)));
 363         }
 364 }
 365
 366 /* Main loop of walsender process */
 367 static int
 368 WalSndLoop(void)
 369 {
 370         char       *output_message;
 371         bool            caughtup = false;
 372
 373         /*
 374          * Allocate buffer that will be used for each output message.  We do this
 375          * just once to reduce palloc overhead.  The buffer must be made large
 376          * enough for maximum-sized messages.
 377          */
 378         output_message = palloc(1 + sizeof(WalDataMessageHeader) + MAX_SEND_SIZE);
 379
 380         /* Loop forever, unless we get an error */
 381         for (;;)
 382         {
 383                 long            remain;         /* remaining time (us) */
 384
 385                 /*
 386                  * Emergency bailout if postmaster has died.  This is to avoid the
 387                  * necessity for manual cleanup of all postmaster children.
 388                  */
 389                 if (!PostmasterIsAlive(true))
 390                         exit(1);
 391
 392                 /* Process any requests or signals received recently */
 393                 if (got_SIGHUP)
 394                 {
 395                         got_SIGHUP = false;
 396                         ProcessConfigFile(PGC_SIGHUP);
 397                 }
 398
 399                 /*
 400                  * When SIGUSR2 arrives, we send all outstanding logs up to the
 401                  * shutdown checkpoint record (i.e., the latest record) and exit.
 402                  */
 403                 if (ready_to_stop)
 404                 {
 405                         if (!XLogSend(output_message, &caughtup))
 406                                 break;
 407                         if (caughtup)
 408                                 shutdown_requested = true;
 409                 }
 410
 411                 /* Normal exit from the walsender is here */
 412                 if (shutdown_requested)
 413                 {
 414                         /* Inform the standby that XLOG streaming was done */
 415                         pq_puttextmessage('C', "COPY 0");
 416                         pq_flush();
 417
 418                         proc_exit(0);
 419                 }
 420
 421                 /*
 422                  * If we had sent all accumulated WAL in last round, nap for the
 423                  * configured time before retrying.
 424                  *
 425                  * On some platforms, signals won't interrupt the sleep.  To ensure we
 426                  * respond reasonably promptly when someone signals us, break down the
 427                  * sleep into NAPTIME_PER_CYCLE increments, and check for interrupts
 428                  * after each nap.
 429                  */
 430                 if (caughtup)
 431                 {
 432                         remain = WalSndDelay * 1000L;
 433                         while (remain > 0)
 434                         {
 435                                 /* Check for interrupts */
 436                                 if (got_SIGHUP || shutdown_requested || ready_to_stop)
 437                                         break;
 438
 439                                 /* Sleep and check that the connection is still alive */
 440                                 pg_usleep(remain > NAPTIME_PER_CYCLE ? NAPTIME_PER_CYCLE : remain);
 441                                 CheckClosedConnection();
 442
 443                                 remain -= NAPTIME_PER_CYCLE;
 444                         }
 445                 }
 446
 447                 /* Attempt to send the log once every loop */
 448                 if (!XLogSend(output_message, &caughtup))
 449                         break;
 450         }
 451
 452         /*
 453          * Get here on send failure.  Clean up and exit.
 454          *
 455          * Reset whereToSendOutput to prevent ereport from attempting to send any
 456          * more messages to the standby.
 457          */
 458         if (whereToSendOutput == DestRemote)
 459                 whereToSendOutput = DestNone;
 460
 461         proc_exit(0);
 462         return 1;                                       /* keep the compiler quiet */
 463 }
 464
 465 /* Initialize a per-walsender data structure for this walsender process */
 466 static void
 467 InitWalSnd(void)
 468 {
 469         int                     i;
 470
 471         /*
 472          * WalSndCtl should be set up already (we inherit this by fork() or
 473          * EXEC_BACKEND mechanism from the postmaster).
 474          */
 475         Assert(WalSndCtl != NULL);
 476         Assert(MyWalSnd == NULL);
 477
 478         /*
 479          * Find a free walsender slot and reserve it. If this fails, we must be
 480          * out of WalSnd structures.
 481          */
 482         for (i = 0; i < max_wal_senders; i++)
 483         {
 484                 /* use volatile pointer to prevent code rearrangement */
 485                 volatile WalSnd *walsnd = &WalSndCtl->walsnds[i];
 486
 487                 SpinLockAcquire(&walsnd->mutex);
 488
 489                 if (walsnd->pid != 0)
 490                 {
 491                         SpinLockRelease(&walsnd->mutex);
 492                         continue;
 493                 }
 494                 else
 495                 {
 496                         /* found */
 497                         MyWalSnd = (WalSnd *) walsnd;
 498                         walsnd->pid = MyProcPid;
 499                         MemSet(&MyWalSnd->sentPtr, 0, sizeof(XLogRecPtr));
 500                         SpinLockRelease(&walsnd->mutex);
 501                         break;
 502                 }
 503         }
 504         if (MyWalSnd == NULL)
 505                 ereport(FATAL,
 506                                 (errcode(ERRCODE_TOO_MANY_CONNECTIONS),
 507                                  errmsg("number of requested standby connections "
 508                                                 "exceeds max_wal_senders (currently %d)",
 509                                                 max_wal_senders)));
 510
 511         /* Arrange to clean up at walsender exit */
 512         on_shmem_exit(WalSndKill, 0);
 513 }
 514
 515 /* Destroy the per-walsender data structure for this walsender process */
 516 static void
 517 WalSndKill(int code, Datum arg)
 518 {
 519         Assert(MyWalSnd != NULL);
 520
 521         /*
 522          * Mark WalSnd struct no longer in use. Assume that no lock is required
 523          * for this.
 524          */
 525         MyWalSnd->pid = 0;
 526
 527         /* WalSnd struct isn't mine anymore */
 528         MyWalSnd = NULL;
 529 }
 530
 531 /*
 532  * Read 'nbytes' bytes from WAL into 'buf', starting at location 'recptr'
 533  *
 534  * XXX probably this should be improved to suck data directly from the
 535  * WAL buffers when possible.
 536  */
 537 static void
 538 XLogRead(char *buf, XLogRecPtr recptr, Size nbytes)
 539 {
 540         XLogRecPtr      startRecPtr = recptr;
 541         char            path[MAXPGPATH];
 542         uint32          lastRemovedLog;
 543         uint32          lastRemovedSeg;
 544         uint32          log;
 545         uint32          seg;
 546
 547         while (nbytes > 0)
 548         {
 549                 uint32          startoff;
 550                 int                     segbytes;
 551                 int                     readbytes;
 552
 553                 startoff = recptr.xrecoff % XLogSegSize;
 554
 555                 if (sendFile < 0 || !XLByteInSeg(recptr, sendId, sendSeg))
 556                 {
 557                         /* Switch to another logfile segment */
 558                         if (sendFile >= 0)
 559                                 close(sendFile);
 560
 561                         XLByteToSeg(recptr, sendId, sendSeg);
 562                         XLogFilePath(path, ThisTimeLineID, sendId, sendSeg);
 563
 564                         sendFile = BasicOpenFile(path, O_RDONLY | PG_BINARY, 0);
 565                         if (sendFile < 0)
 566                         {
 567                                 /*
 568                                  * If the file is not found, assume it's because the standby
 569                                  * asked for a too old WAL segment that has already been
 570                                  * removed or recycled.
 571                                  */
 572                                 if (errno == ENOENT)
 573                                 {
 574                                         char            filename[MAXFNAMELEN];
 575
 576                                         XLogFileName(filename, ThisTimeLineID, sendId, sendSeg);
 577                                         ereport(ERROR,
 578                                                         (errcode_for_file_access(),
 579                                                          errmsg("requested WAL segment %s has already been removed",
 580                                                                         filename)));
 581                                 }
 582                                 else
 583                                         ereport(ERROR,
 584                                                         (errcode_for_file_access(),
 585                                                          errmsg("could not open file \"%s\" (log file %u, segment %u): %m",
 586                                                                         path, sendId, sendSeg)));
 587                         }
 588                         sendOff = 0;
 589                 }
 590
 591                 /* Need to seek in the file? */
 592                 if (sendOff != startoff)
 593                 {
 594                         if (lseek(sendFile, (off_t) startoff, SEEK_SET) < 0)
 595                                 ereport(ERROR,
 596                                                 (errcode_for_file_access(),
 597                                                  errmsg("could not seek in log file %u, segment %u to offset %u: %m",
 598                                                                 sendId, sendSeg, startoff)));
 599                         sendOff = startoff;
 600                 }
 601
 602                 /* How many bytes are within this segment? */
 603                 if (nbytes > (XLogSegSize - startoff))
 604                         segbytes = XLogSegSize - startoff;
 605                 else
 606                         segbytes = nbytes;
 607
 608                 readbytes = read(sendFile, buf, segbytes);
 609                 if (readbytes <= 0)
 610                         ereport(ERROR,
 611                                         (errcode_for_file_access(),
 612                         errmsg("could not read from log file %u, segment %u, offset %u, "
 613                                    "length %lu: %m",
 614                                    sendId, sendSeg, sendOff, (unsigned long) segbytes)));
 615
 616                 /* Update state for read */
 617                 XLByteAdvance(recptr, readbytes);
 618
 619                 sendOff += readbytes;
 620                 nbytes -= readbytes;
 621                 buf += readbytes;
 622         }
 623
 624         /*
 625          * After reading into the buffer, check that what we read was valid. We do
 626          * this after reading, because even though the segment was present when we
 627          * opened it, it might get recycled or removed while we read it. The
 628          * read() succeeds in that case, but the data we tried to read might
 629          * already have been overwritten with new WAL records.
 630          */
 631         XLogGetLastRemoved(&lastRemovedLog, &lastRemovedSeg);
 632         XLByteToSeg(startRecPtr, log, seg);
 633         if (log < lastRemovedLog ||
 634                 (log == lastRemovedLog && seg <= lastRemovedSeg))
 635         {
 636                 char            filename[MAXFNAMELEN];
 637
 638                 XLogFileName(filename, ThisTimeLineID, log, seg);
 639                 ereport(ERROR,
 640                                 (errcode_for_file_access(),
 641                                  errmsg("requested WAL segment %s has already been removed",
 642                                                 filename)));
 643         }
 644 }
 645
 646 /*
 647  * Read up to MAX_SEND_SIZE bytes of WAL that's been flushed to disk,
 648  * but not yet sent to the client, and send it.
 649  *
 650  * msgbuf is a work area in which the output message is constructed.  It's
 651  * passed in just so we can avoid re-palloc'ing the buffer on each cycle.
 652  * It must be of size 1 + sizeof(WalDataMessageHeader) + MAX_SEND_SIZE.
 653  *
 654  * If there is no unsent WAL remaining, *caughtup is set to true, otherwise
 655  * *caughtup is set to false.
 656  *
 657  * Returns true if OK, false if trouble.
 658  */
 659 static bool
 660 XLogSend(char *msgbuf, bool *caughtup)
 661 {
 662         XLogRecPtr      SendRqstPtr;
 663         XLogRecPtr      startptr;
 664         XLogRecPtr      endptr;
 665         Size            nbytes;
 666         WalDataMessageHeader msghdr;
 667
 668         /*
 669          * Attempt to send all data that's already been written out and fsync'd to
 670          * disk.  We cannot go further than what's been written out given the
 671          * current implementation of XLogRead().  And in any case it's unsafe to
 672          * send WAL that is not securely down to disk on the master: if the master
 673          * subsequently crashes and restarts, slaves must not have applied any WAL
 674          * that gets lost on the master.
 675          */
 676         SendRqstPtr = GetFlushRecPtr();
 677
 678         /* Quick exit if nothing to do */
 679         if (XLByteLE(SendRqstPtr, sentPtr))
 680         {
 681                 *caughtup = true;
 682                 return true;
 683         }
 684
 685         /*
 686          * Figure out how much to send in one message. If there's no more than
 687          * MAX_SEND_SIZE bytes to send, send everything. Otherwise send
 688          * MAX_SEND_SIZE bytes, but round back to logfile or page boundary.
 689          *
 690          * The rounding is not only for performance reasons. Walreceiver relies on
 691          * the fact that we never split a WAL record across two messages. Since a
 692          * long WAL record is split at page boundary into continuation records,
 693          * page boundary is always a safe cut-off point. We also assume that
 694          * SendRqstPtr never points to the middle of a WAL record.
 695          */
 696         startptr = sentPtr;
 697         if (startptr.xrecoff >= XLogFileSize)
 698         {
 699                 /*
 700                  * crossing a logid boundary, skip the non-existent last log segment
 701                  * in previous logical log file.
 702                  */
 703                 startptr.xlogid += 1;
 704                 startptr.xrecoff = 0;
 705         }
 706
 707         endptr = startptr;
 708         XLByteAdvance(endptr, MAX_SEND_SIZE);
 709         if (endptr.xlogid != startptr.xlogid)
 710         {
 711                 /* Don't cross a logfile boundary within one message */
 712                 Assert(endptr.xlogid == startptr.xlogid + 1);
 713                 endptr.xlogid = startptr.xlogid;
 714                 endptr.xrecoff = XLogFileSize;
 715         }
 716
 717         /* if we went beyond SendRqstPtr, back off */
 718         if (XLByteLE(SendRqstPtr, endptr))
 719         {
 720                 endptr = SendRqstPtr;
 721                 *caughtup = true;
 722         }
 723         else
 724         {
 725                 /* round down to page boundary. */
 726                 endptr.xrecoff -= (endptr.xrecoff % XLOG_BLCKSZ);
 727                 *caughtup = false;
 728         }
 729
 730         nbytes = endptr.xrecoff - startptr.xrecoff;
 731         Assert(nbytes <= MAX_SEND_SIZE);
 732
 733         /*
 734          * OK to read and send the slice.
 735          */
 736         msgbuf[0] = 'w';
 737
 738         /*
 739          * Read the log directly into the output buffer to avoid extra memcpy
 740          * calls.
 741          */
 742         XLogRead(msgbuf + 1 + sizeof(WalDataMessageHeader), startptr, nbytes);
 743
 744         /*
 745          * We fill the message header last so that the send timestamp is taken as
 746          * late as possible.
 747          */
 748         msghdr.dataStart = startptr;
 749         msghdr.walEnd = SendRqstPtr;
 750         msghdr.sendTime = GetCurrentTimestamp();
 751
 752         memcpy(msgbuf + 1, &msghdr, sizeof(WalDataMessageHeader));
 753
 754         pq_putmessage('d', msgbuf, 1 + sizeof(WalDataMessageHeader) + nbytes);
 755
 756         /* Flush pending output to the client */
 757         if (pq_flush())
 758                 return false;
 759
 760         sentPtr = endptr;
 761
 762         /* Update shared memory status */
 763         {
 764                 /* use volatile pointer to prevent code rearrangement */
 765                 volatile WalSnd *walsnd = MyWalSnd;
 766
 767                 SpinLockAcquire(&walsnd->mutex);
 768                 walsnd->sentPtr = sentPtr;
 769                 SpinLockRelease(&walsnd->mutex);
 770         }
 771
 772         /* Report progress of XLOG streaming in PS display */
 773         if (update_process_title)
 774         {
 775                 char            activitymsg[50];
 776
 777                 snprintf(activitymsg, sizeof(activitymsg), "streaming %X/%X",
 778                                  sentPtr.xlogid, sentPtr.xrecoff);
 779                 set_ps_display(activitymsg, false);
 780         }
 781
 782         return true;
 783 }
 784
 785 /* SIGHUP: set flag to re-read config file at next convenient time */
 786 static void
 787 WalSndSigHupHandler(SIGNAL_ARGS)
 788 {
 789         got_SIGHUP = true;
 790 }
 791
 792 /* SIGTERM: set flag to shut down */
 793 static void
 794 WalSndShutdownHandler(SIGNAL_ARGS)
 795 {
 796         shutdown_requested = true;
 797 }
 798
 799 /*
 800  * WalSndQuickDieHandler() occurs when signalled SIGQUIT by the postmaster.
 801  *
 802  * Some backend has bought the farm,
 803  * so we need to stop what we're doing and exit.
 804  */
 805 static void
 806 WalSndQuickDieHandler(SIGNAL_ARGS)
 807 {
 808         PG_SETMASK(&BlockSig);
 809
 810         /*
 811          * We DO NOT want to run proc_exit() callbacks -- we're here because
 812          * shared memory may be corrupted, so we don't want to try to clean up our
 813          * transaction.  Just nail the windows shut and get out of town.  Now that
 814          * there's an atexit callback to prevent third-party code from breaking
 815          * things by calling exit() directly, we have to reset the callbacks
 816          * explicitly to make this work as intended.
 817          */
 818         on_exit_reset();
 819
 820         /*
 821          * Note we do exit(2) not exit(0).      This is to force the postmaster into a
 822          * system reset cycle if some idiot DBA sends a manual SIGQUIT to a random
 823          * backend.  This is necessary precisely because we don't clean up our
 824          * shared memory state.  (The "dead man switch" mechanism in pmsignal.c
 825          * should ensure the postmaster sees this as a crash, too, but no harm in
 826          * being doubly sure.)
 827          */
 828         exit(2);
 829 }
 830
 831 /* SIGUSR2: set flag to do a last cycle and shut down afterwards */
 832 static void
 833 WalSndLastCycleHandler(SIGNAL_ARGS)
 834 {
 835         ready_to_stop = true;
 836 }
 837
 838 /* Set up signal handlers */
 839 void
 840 WalSndSignals(void)
 841 {
 842         /* Set up signal handlers */
 843         pqsignal(SIGHUP, WalSndSigHupHandler);          /* set flag to read config
 844                                                                                                  * file */
 845         pqsignal(SIGINT, SIG_IGN);      /* not used */
 846         pqsignal(SIGTERM, WalSndShutdownHandler);       /* request shutdown */
 847         pqsignal(SIGQUIT, WalSndQuickDieHandler);       /* hard crash time */
 848         pqsignal(SIGALRM, SIG_IGN);
 849         pqsignal(SIGPIPE, SIG_IGN);
 850         pqsignal(SIGUSR1, SIG_IGN); /* not used */
 851         pqsignal(SIGUSR2, WalSndLastCycleHandler);      /* request a last cycle and
 852                                                                                                  * shutdown */
 853
 854         /* Reset some signals that are accepted by postmaster but not here */
 855         pqsignal(SIGCHLD, SIG_DFL);
 856         pqsignal(SIGTTIN, SIG_DFL);
 857         pqsignal(SIGTTOU, SIG_DFL);
 858         pqsignal(SIGCONT, SIG_DFL);
 859         pqsignal(SIGWINCH, SIG_DFL);
 860 }
 861
 862 /* Report shared-memory space needed by WalSndShmemInit */
 863 Size
 864 WalSndShmemSize(void)
 865 {
 866         Size            size = 0;
 867
 868         size = offsetof(WalSndCtlData, walsnds);
 869         size = add_size(size, mul_size(max_wal_senders, sizeof(WalSnd)));
 870
 871         return size;
 872 }
 873
 874 /* Allocate and initialize walsender-related shared memory */
 875 void
 876 WalSndShmemInit(void)
 877 {
 878         bool            found;
 879         int                     i;
 880
 881         WalSndCtl = (WalSndCtlData *)
 882                 ShmemInitStruct("Wal Sender Ctl", WalSndShmemSize(), &found);
 883
 884         if (!found)
 885         {
 886                 /* First time through, so initialize */
 887                 MemSet(WalSndCtl, 0, WalSndShmemSize());
 888
 889                 for (i = 0; i < max_wal_senders; i++)
 890                 {
 891                         WalSnd     *walsnd = &WalSndCtl->walsnds[i];
 892
 893                         SpinLockInit(&walsnd->mutex);
 894                 }
 895         }
 896 }
 897
 898 /*
 899  * This isn't currently used for anything. Monitoring tools might be
 900  * interested in the future, and we'll need something like this in the
 901  * future for synchronous replication.
 902  */
 903 #ifdef NOT_USED
 904 /*
 905  * Returns the oldest Send position among walsenders. Or InvalidXLogRecPtr
 906  * if none.
 907  */
 908 XLogRecPtr
 909 GetOldestWALSendPointer(void)
 910 {
 911         XLogRecPtr      oldest = {0, 0};
 912         int                     i;
 913         bool            found = false;
 914
 915         for (i = 0; i < max_wal_senders; i++)
 916         {
 917                 /* use volatile pointer to prevent code rearrangement */
 918                 volatile WalSnd *walsnd = &WalSndCtl->walsnds[i];
 919                 XLogRecPtr      recptr;
 920
 921                 if (walsnd->pid == 0)
 922                         continue;
 923
 924                 SpinLockAcquire(&walsnd->mutex);
 925                 recptr = walsnd->sentPtr;
 926                 SpinLockRelease(&walsnd->mutex);
 927
 928                 if (recptr.xlogid == 0 && recptr.xrecoff == 0)
 929                         continue;
 930
 931                 if (!found || XLByteLT(recptr, oldest))
 932                         oldest = recptr;
 933                 found = true;
 934         }
 935         return oldest;
 936 }
 937
 938 #endif