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 8.5. It takes
   6  * charge of XLOG streaming sender in the primary server. At first, it is
   7  * started by the postmaster when the walreceiver in the standby server
   8  * connects to the primary server and requests XLOG streaming replication,
   9  * i.e., unlike any auxiliary process, it is not an always-running process.
  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 an 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  * Note that there can be more than one walsender process concurrently.
  28  *
  29  * Portions Copyright (c) 2010-2010, PostgreSQL Global Development Group
  30  *
  31  *
  32  * IDENTIFICATION
  33  *        $PostgreSQL: pgsql/src/backend/replication/walsender.c,v 1.5 2010/02/03 09:47:19 heikki Exp $
  34  *
  35  *-------------------------------------------------------------------------
  36  */
  37 #include "postgres.h"
  38
  39 #include <unistd.h>
  40
  41 #include "access/xlog_internal.h"
  42 #include "catalog/pg_type.h"
  43 #include "libpq/libpq.h"
  44 #include "libpq/pqformat.h"
  45 #include "libpq/pqsignal.h"
  46 #include "miscadmin.h"
  47 #include "replication/walsender.h"
  48 #include "storage/fd.h"
  49 #include "storage/ipc.h"
  50 #include "storage/lock.h"
  51 #include "storage/pmsignal.h"
  52 #include "tcop/tcopprot.h"
  53 #include "utils/guc.h"
  54 #include "utils/memutils.h"
  55 #include "utils/ps_status.h"
  56
  57 /* Array of WalSnds in shared memory */
  58 WalSndCtlData *WalSndCtl = NULL;
  59
  60 /* My slot in the shared memory array */
  61 static WalSnd *MyWalSnd = NULL;
  62
  63 /* Global state */
  64 bool    am_walsender    = false;        /* Am I a walsender process ? */
  65
  66 /* User-settable parameters for walsender */
  67 int     MaxWalSenders = 0;              /* the maximum number of concurrent walsenders */
  68 int     WalSndDelay     = 200;          /* max sleep time between some actions */
  69
  70 #define NAPTIME_PER_CYCLE 100   /* max sleep time between cycles (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.
  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
  97 /* Prototypes for private functions */
  98 static int      WalSndLoop(void);
  99 static void     InitWalSnd(void);
 100 static void     WalSndHandshake(void);
 101 static void     WalSndKill(int code, Datum arg);
 102 static void XLogRead(char *buf, XLogRecPtr recptr, Size nbytes);
 103 static bool XLogSend(StringInfo outMsg);
 104 static void CheckClosedConnection(void);
 105
 106 /*
 107  * How much WAL to send in one message? Must be >= XLOG_BLCKSZ.
 108  */
 109 #define MAX_SEND_SIZE (XLOG_SEG_SIZE / 2)
 110
 111 /* Main entry point for walsender process */
 112 int
 113 WalSenderMain(void)
 114 {
 115         MemoryContext walsnd_context;
 116
 117         if (!superuser())
 118                 ereport(FATAL,
 119                                 (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
 120                                  errmsg("must be superuser to start walsender")));
 121
 122         /* Create a per-walsender data structure in shared memory */
 123         InitWalSnd();
 124
 125         /*
 126          * Create a memory context that we will do all our work in.  We do this so
 127          * that we can reset the context during error recovery and thereby avoid
 128          * possible memory leaks.  Formerly this code just ran in
 129          * TopMemoryContext, but resetting that would be a really bad idea.
 130          *
 131          * XXX: we don't actually attempt error recovery in walsender, we just
 132          * close the connection and exit.
 133          */
 134         walsnd_context = AllocSetContextCreate(TopMemoryContext,
 135                                                                                    "Wal Sender",
 136                                                                                    ALLOCSET_DEFAULT_MINSIZE,
 137                                                                                    ALLOCSET_DEFAULT_INITSIZE,
 138                                                                                    ALLOCSET_DEFAULT_MAXSIZE);
 139         MemoryContextSwitchTo(walsnd_context);
 140
 141         /* Unblock signals (they were blocked when the postmaster forked us) */
 142         PG_SETMASK(&UnBlockSig);
 143
 144         /* Tell the standby that walsender is ready for receiving commands */
 145         ReadyForQuery(DestRemote);
 146
 147         /* Handle handshake messages before streaming */
 148         WalSndHandshake();
 149
 150         /* Main loop of walsender */
 151         return WalSndLoop();
 152 }
 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                  * Check for any other interesting events that happened while we
 171                  * slept.
 172                  */
 173                 if (got_SIGHUP)
 174                 {
 175                         got_SIGHUP = false;
 176                         ProcessConfigFile(PGC_SIGHUP);
 177                 }
 178
 179                 if (firstchar == EOF)
 180                 {
 181                         /* standby disconnected */
 182                         ereport(COMMERROR,
 183                                         (errcode(ERRCODE_PROTOCOL_VIOLATION),
 184                                          errmsg("unexpected EOF on standby connection")));
 185                 }
 186                 else
 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
 197                 /* Handle the very limited subset of commands expected in this phase */
 198
 199                 switch (firstchar)
 200                 {
 201                         case 'Q':       /* Query message */
 202                         {
 203                                 const char *query_string;
 204                                 XLogRecPtr      recptr;
 205
 206                                 query_string = pq_getmsgstring(&input_message);
 207                                 pq_getmsgend(&input_message);
 208
 209                                 if (strcmp(query_string, "IDENTIFY_SYSTEM") == 0)
 210                                 {
 211                                         StringInfoData  buf;
 212                                         char    sysid[32];
 213                                         char    tli[11];
 214
 215                                         /*
 216                                          * Reply with a result set with one row, two columns.
 217                                          * First col is system ID, and second if timeline ID
 218                                          */
 219
 220                                         snprintf(sysid, sizeof(sysid), UINT64_FORMAT,
 221                                                          GetSystemIdentifier());
 222                                         snprintf(tli, sizeof(tli), "%u", ThisTimeLineID);
 223
 224                                         /* Send a RowDescription message */
 225                                         pq_beginmessage(&buf, 'T');
 226                                         pq_sendint(&buf, 2, 2); /* 2 fields */
 227
 228                                         /* first field */
 229                                         pq_sendstring(&buf, "systemid"); /* col name */
 230                                         pq_sendint(&buf, 0, 4);                 /* table oid */
 231                                         pq_sendint(&buf, 0, 2);                 /* attnum */
 232                                         pq_sendint(&buf, TEXTOID, 4);   /* type oid */
 233                                         pq_sendint(&buf, -1, 2);                /* typlen */
 234                                         pq_sendint(&buf, 0, 4);                 /* typmod */
 235                                         pq_sendint(&buf, 0, 2);                 /* format code */
 236
 237                                         /* second field */
 238                                         pq_sendstring(&buf, "timeline"); /* col name */
 239                                         pq_sendint(&buf, 0, 4);                 /* table oid */
 240                                         pq_sendint(&buf, 0, 2);                 /* attnum */
 241                                         pq_sendint(&buf, INT4OID, 4);   /* type oid */
 242                                         pq_sendint(&buf, 4, 2);                 /* typlen */
 243                                         pq_sendint(&buf, 0, 4);                 /* typmod */
 244                                         pq_sendint(&buf, 0, 2);                 /* format code */
 245                                         pq_endmessage(&buf);
 246
 247                                         /* Send a DataRow message */
 248                                         pq_beginmessage(&buf, 'D');
 249                                         pq_sendint(&buf, 2, 2);                 /* # of columns */
 250                                         pq_sendint(&buf, strlen(sysid), 4); /* col1 len */
 251                                         pq_sendbytes(&buf, (char *) &sysid, strlen(sysid));
 252                                         pq_sendint(&buf, strlen(tli), 4); /* col2 len */
 253                                         pq_sendbytes(&buf, (char *) tli, strlen(tli));
 254                                         pq_endmessage(&buf);
 255
 256                                         /* Send CommandComplete and ReadyForQuery messages */
 257                                         EndCommand("SELECT", DestRemote);
 258                                         ReadyForQuery(DestRemote);
 259                                 }
 260                                 else if (sscanf(query_string, "START_REPLICATION %X/%X",
 261                                                                 &recptr.xlogid, &recptr.xrecoff) == 2)
 262                                 {
 263                                         StringInfoData  buf;
 264
 265                                         /* Send a CopyOutResponse message, and start streaming */
 266                                         pq_beginmessage(&buf, 'H');
 267                                         pq_sendbyte(&buf, 0);
 268                                         pq_sendint(&buf, 0, 2);
 269                                         pq_endmessage(&buf);
 270
 271                                         /*
 272                                          * Initialize position to the received one, then
 273                                          * the xlog records begin to be shipped from that position
 274                                          */
 275                                         sentPtr = recptr;
 276
 277                                         /* break out of the loop */
 278                                         replication_started = true;
 279                                 }
 280                                 else
 281                                 {
 282                                         ereport(FATAL,
 283                                                         (errcode(ERRCODE_PROTOCOL_VIOLATION),
 284                                                          errmsg("invalid standby query string: %s", query_string)));
 285                                 }
 286                                 break;
 287                         }
 288
 289                         /* 'X' means that the standby is closing the connection */
 290                         case 'X':
 291                                 proc_exit(0);
 292
 293                         case EOF:
 294                                 ereport(ERROR,
 295                                                 (errcode(ERRCODE_PROTOCOL_VIOLATION),
 296                                                  errmsg("unexpected EOF on standby connection")));
 297
 298                         default:
 299                                 ereport(FATAL,
 300                                                 (errcode(ERRCODE_PROTOCOL_VIOLATION),
 301                                                  errmsg("invalid standby handshake message type %d", firstchar)));
 302                 }
 303         }
 304 }
 305
 306 /*
 307  * Check if the remote end has closed the connection.
 308  */
 309 static void
 310 CheckClosedConnection(void)
 311 {
 312         unsigned char firstchar;
 313         int r;
 314
 315         r = pq_getbyte_if_available(&firstchar);
 316         if (r < 0)
 317         {
 318                 /* no data available */
 319                 if (errno == EAGAIN || errno == EWOULDBLOCK)
 320                         return;
 321
 322                 /*
 323                  * Ok if interrupted, though it shouldn't really happen with
 324                  * a non-blocking operation.
 325                  */
 326                 if (errno == EINTR)
 327                         return;
 328
 329                 ereport(COMMERROR,
 330                                 (errcode_for_socket_access(),
 331                                  errmsg("could not receive data from client: %m")));
 332         }
 333         if (r == 0)
 334         {
 335                 /* standby disconnected unexpectedly */
 336                 ereport(ERROR,
 337                                 (errcode(ERRCODE_PROTOCOL_VIOLATION),
 338                                  errmsg("unexpected EOF on standby connection")));
 339         }
 340
 341         /* Handle the very limited subset of commands expected in this phase */
 342         switch (firstchar)
 343         {
 344                 /*
 345                  * 'X' means that the standby is closing down the socket. EOF means
 346                  * unexpected loss of standby connection. Either way, perform normal
 347                  * shutdown.
 348                  */
 349                 case 'X':
 350                         proc_exit(0);
 351
 352                 default:
 353                         ereport(FATAL,
 354                                         (errcode(ERRCODE_PROTOCOL_VIOLATION),
 355                                          errmsg("invalid standby closing message type %d",
 356                                                         firstchar)));
 357         }
 358 }
 359
 360 /* Main loop of walsender process */
 361 static int
 362 WalSndLoop(void)
 363 {
 364         StringInfoData output_message;
 365
 366         initStringInfo(&output_message);
 367
 368         /* Loop forever */
 369         for (;;)
 370         {
 371                 int remain;     /* remaining time (ms) */
 372
 373                 /*
 374                  * Emergency bailout if postmaster has died.  This is to avoid the
 375                  * necessity for manual cleanup of all postmaster children.
 376                  */
 377                 if (!PostmasterIsAlive(true))
 378                         exit(1);
 379                 /* Process any requests or signals received recently */
 380                 if (got_SIGHUP)
 381                 {
 382                         got_SIGHUP = false;
 383                         ProcessConfigFile(PGC_SIGHUP);
 384                 }
 385
 386                 /*
 387                  * When SIGUSR2 arrives, we send all outstanding logs up to the
 388                  * shutdown checkpoint record (i.e., the latest record) and exit.
 389                  */
 390                 if (ready_to_stop)
 391                 {
 392                         XLogSend(&output_message);
 393                         shutdown_requested = true;
 394                 }
 395
 396                 /* Normal exit from the walsender is here */
 397                 if (shutdown_requested)
 398                 {
 399                         /* Inform the standby that XLOG streaming was done */
 400                         pq_puttextmessage('C', "COPY 0");
 401                         pq_flush();
 402
 403                         proc_exit(0);
 404                 }
 405
 406                 /*
 407                  * Nap for the configured time or until a message arrives.
 408                  *
 409                  * On some platforms, signals won't interrupt the sleep.  To ensure we
 410                  * respond reasonably promptly when someone signals us, break down the
 411                  * sleep into NAPTIME_PER_CYCLE (ms) increments, and check for
 412                  * interrupts after each nap.
 413                  */
 414                 remain = WalSndDelay;
 415                 while (remain > 0)
 416                 {
 417                         if (got_SIGHUP || shutdown_requested || ready_to_stop)
 418                                 break;
 419
 420                         /*
 421                          * Check to see whether a message from the standby or an interrupt
 422                          * from other processes has arrived.
 423                          */
 424                         pg_usleep(remain > NAPTIME_PER_CYCLE ? NAPTIME_PER_CYCLE : remain);
 425                         CheckClosedConnection();
 426
 427                         remain -= NAPTIME_PER_CYCLE;
 428                 }
 429
 430                 /* Attempt to send the log once every loop */
 431                 if (!XLogSend(&output_message))
 432                         goto eof;
 433         }
 434
 435         /* can't get here because the above loop never exits */
 436         return 1;
 437
 438 eof:
 439         /*
 440          * Reset whereToSendOutput to prevent ereport from attempting
 441          * to send any more messages to the standby.
 442          */
 443         if (whereToSendOutput == DestRemote)
 444                 whereToSendOutput = DestNone;
 445
 446         proc_exit(0);
 447         return 1;               /* keep the compiler quiet */
 448 }
 449
 450 /* Initialize a per-walsender data structure for this walsender process */
 451 static void
 452 InitWalSnd(void)
 453 {
 454         /* use volatile pointer to prevent code rearrangement */
 455         int             i;
 456
 457         /*
 458          * WalSndCtl should be set up already (we inherit this by fork() or
 459          * EXEC_BACKEND mechanism from the postmaster).
 460          */
 461         Assert(WalSndCtl != NULL);
 462         Assert(MyWalSnd == NULL);
 463
 464         /*
 465          * Find a free walsender slot and reserve it. If this fails, we must be
 466          * out of WalSnd structures.
 467          */
 468         for (i = 0; i < MaxWalSenders; i++)
 469         {
 470                 volatile WalSnd *walsnd = &WalSndCtl->walsnds[i];
 471
 472                 SpinLockAcquire(&walsnd->mutex);
 473
 474                 if (walsnd->pid != 0)
 475                 {
 476                         SpinLockRelease(&walsnd->mutex);
 477                         continue;
 478                 }
 479                 else
 480                 {
 481                         /* found */
 482                         MyWalSnd = (WalSnd *) walsnd;
 483                         walsnd->pid = MyProcPid;
 484                         MemSet(&MyWalSnd->sentPtr, 0, sizeof(XLogRecPtr));
 485                         SpinLockRelease(&walsnd->mutex);
 486                         break;
 487                 }
 488         }
 489         if (MyWalSnd == NULL)
 490                 ereport(FATAL,
 491                                 (errcode(ERRCODE_TOO_MANY_CONNECTIONS),
 492                                  errmsg("sorry, too many standbys already")));
 493
 494         /* Arrange to clean up at walsender exit */
 495         on_shmem_exit(WalSndKill, 0);
 496 }
 497
 498 /* Destroy the per-walsender data structure for this walsender process */
 499 static void
 500 WalSndKill(int code, Datum arg)
 501 {
 502         Assert(MyWalSnd != NULL);
 503
 504         /*
 505          * Mark WalSnd struct no longer in use. Assume that no lock is required
 506          * for this.
 507          */
 508         MyWalSnd->pid = 0;
 509
 510         /* WalSnd struct isn't mine anymore */
 511         MyWalSnd = NULL;
 512 }
 513
 514 /*
 515  * Read 'nbytes' bytes from WAL into 'buf', starting at location 'recptr'
 516  */
 517 void
 518 XLogRead(char *buf, XLogRecPtr recptr, Size nbytes)
 519 {
 520         char path[MAXPGPATH];
 521         uint32 startoff;
 522
 523         while (nbytes > 0)
 524         {
 525                 int segbytes;
 526                 int readbytes;
 527
 528                 startoff = recptr.xrecoff % XLogSegSize;
 529
 530                 if (sendFile < 0 || !XLByteInSeg(recptr, sendId, sendSeg))
 531                 {
 532                         /* Switch to another logfile segment */
 533                         if (sendFile >= 0)
 534                                 close(sendFile);
 535
 536                         XLByteToSeg(recptr, sendId, sendSeg);
 537                         XLogFilePath(path, ThisTimeLineID, sendId, sendSeg);
 538
 539                         sendFile = BasicOpenFile(path, O_RDONLY | PG_BINARY, 0);
 540                         if (sendFile < 0)
 541                                 ereport(FATAL, /* XXX: Why FATAL? */
 542                                                 (errcode_for_file_access(),
 543                                                  errmsg("could not open file \"%s\" (log file %u, segment %u): %m",
 544                                                                 path, sendId, sendSeg)));
 545                         sendOff = 0;
 546                 }
 547
 548                 /* Need to seek in the file? */
 549                 if (sendOff != startoff)
 550                 {
 551                         if (lseek(sendFile, (off_t) startoff, SEEK_SET) < 0)
 552                                 ereport(FATAL,
 553                                                 (errcode_for_file_access(),
 554                                                  errmsg("could not seek in log file %u, segment %u to offset %u: %m",
 555                                                                 sendId, sendSeg, startoff)));
 556                         sendOff = startoff;
 557                 }
 558
 559                 /* How many bytes are within this segment? */
 560                 if (nbytes > (XLogSegSize - startoff))
 561                         segbytes = XLogSegSize - startoff;
 562                 else
 563                         segbytes = nbytes;
 564
 565                 readbytes = read(sendFile, buf, segbytes);
 566                 if (readbytes <= 0)
 567                         ereport(FATAL,
 568                                         (errcode_for_file_access(),
 569                                          errmsg("could not read from log file %u, segment %u, offset %u, "
 570                                                         "length %lu: %m",
 571                                                         sendId, sendSeg, sendOff, (unsigned long) segbytes)));
 572
 573                 /* Update state for read */
 574                 XLByteAdvance(recptr, readbytes);
 575
 576                 sendOff += readbytes;
 577                 nbytes -= readbytes;
 578                 buf += readbytes;
 579         }
 580 }
 581
 582 /*
 583  * Read all WAL that's been written (and flushed) since last cycle, and send
 584  * it to client.
 585  *
 586  * Returns true if OK, false if trouble.
 587  */
 588 static bool
 589 XLogSend(StringInfo outMsg)
 590 {
 591         XLogRecPtr      SendRqstPtr;
 592         char    activitymsg[50];
 593         /* use volatile pointer to prevent code rearrangement */
 594         volatile WalSnd *walsnd = MyWalSnd;
 595
 596         /*
 597          * Invalid position means that we have not yet received the initial
 598          * CopyData message from the slave that indicates where to start the
 599          * streaming.
 600          */
 601         if (sentPtr.xlogid == 0 &&
 602                 sentPtr.xrecoff == 0)
 603                 return true;
 604
 605         /* Attempt to send all records flushed to the disk already */
 606         SendRqstPtr = GetWriteRecPtr();
 607
 608         /* Quick exit if nothing to do */
 609         if (!XLByteLT(sentPtr, SendRqstPtr))
 610                 return true;
 611
 612         /*
 613          * We gather multiple records together by issuing just one XLogRead()
 614          * of a suitable size, and send them as one CopyData message. Repeat
 615          * until we've sent everything we can.
 616          */
 617         while (XLByteLT(sentPtr, SendRqstPtr))
 618         {
 619                 XLogRecPtr startptr;
 620                 XLogRecPtr endptr;
 621                 Size    nbytes;
 622
 623                 /*
 624                  * Figure out how much to send in one message. If there's less than
 625                  * MAX_SEND_SIZE bytes to send, send everything. Otherwise send
 626                  * MAX_SEND_SIZE bytes, but round to page boundary.
 627                  *
 628                  * The rounding is not only for performance reasons. Walreceiver
 629                  * relies on the fact that we never split a WAL record across two
 630                  * messages. Since a long WAL record is split at page boundary into
 631                  * continuation records, page boundary is always a safe cut-off point.
 632                  * We also assume that SendRqstPtr never points in the middle of a
 633                  * WAL record.
 634                  */
 635                 startptr = sentPtr;
 636                 if (startptr.xrecoff >= XLogFileSize)
 637                 {
 638                         /*
 639                          * crossing a logid boundary, skip the non-existent last log
 640                          * segment in previous logical log file.
 641                          */
 642                         startptr.xlogid += 1;
 643                         startptr.xrecoff = 0;
 644                 }
 645
 646                 endptr = startptr;
 647                 XLByteAdvance(endptr, MAX_SEND_SIZE);
 648                 /* round down to page boundary. */
 649                 endptr.xrecoff -= (endptr.xrecoff % XLOG_BLCKSZ);
 650                 /* if we went beyond SendRqstPtr, back off */
 651                 if (XLByteLT(SendRqstPtr, endptr))
 652                         endptr = SendRqstPtr;
 653
 654                 /*
 655                  * OK to read and send the slice.
 656                  *
 657                  * We don't need to convert the xlogid/xrecoff from host byte order
 658                  * to network byte order because the both server can be expected to
 659                  * have the same byte order. If they have different byte order, we
 660                  * don't reach here.
 661                  */
 662                 pq_sendbyte(outMsg, 'w');
 663                 pq_sendbytes(outMsg, (char *) &startptr, sizeof(startptr));
 664
 665                 if (endptr.xlogid != startptr.xlogid)
 666                 {
 667                         Assert(endptr.xlogid == startptr.xlogid + 1);
 668                         nbytes = endptr.xrecoff + XLogFileSize - startptr.xrecoff;
 669                 }
 670                 else
 671                         nbytes = endptr.xrecoff - startptr.xrecoff;
 672
 673                 sentPtr = endptr;
 674
 675                 /*
 676                  * Read the log directly into the output buffer to prevent
 677                  * extra memcpy calls.
 678                  */
 679                 enlargeStringInfo(outMsg, nbytes);
 680
 681                 XLogRead(&outMsg->data[outMsg->len], startptr, nbytes);
 682                 outMsg->len += nbytes;
 683                 outMsg->data[outMsg->len] = '\0';
 684
 685                 pq_putmessage('d', outMsg->data, outMsg->len);
 686                 resetStringInfo(outMsg);
 687         }
 688
 689         /* Update shared memory status */
 690         SpinLockAcquire(&walsnd->mutex);
 691         walsnd->sentPtr = sentPtr;
 692         SpinLockRelease(&walsnd->mutex);
 693
 694         /* Flush pending output */
 695         if (pq_flush())
 696                 return false;
 697
 698         /* Report progress of XLOG streaming in PS display */
 699         snprintf(activitymsg, sizeof(activitymsg), "streaming %X/%X",
 700                          sentPtr.xlogid, sentPtr.xrecoff);
 701         set_ps_display(activitymsg, false);
 702
 703         return true;
 704 }
 705
 706 /* SIGHUP: set flag to re-read config file at next convenient time */
 707 static void
 708 WalSndSigHupHandler(SIGNAL_ARGS)
 709 {
 710         got_SIGHUP = true;
 711 }
 712
 713 /* SIGTERM: set flag to shut down */
 714 static void
 715 WalSndShutdownHandler(SIGNAL_ARGS)
 716 {
 717         shutdown_requested = true;
 718 }
 719
 720 /*
 721  * WalSndQuickDieHandler() occurs when signalled SIGQUIT by the postmaster.
 722  *
 723  * Some backend has bought the farm,
 724  * so we need to stop what we're doing and exit.
 725  */
 726 static void
 727 WalSndQuickDieHandler(SIGNAL_ARGS)
 728 {
 729         PG_SETMASK(&BlockSig);
 730
 731         /*
 732          * We DO NOT want to run proc_exit() callbacks -- we're here because
 733          * shared memory may be corrupted, so we don't want to try to clean up our
 734          * transaction.  Just nail the windows shut and get out of town.  Now that
 735          * there's an atexit callback to prevent third-party code from breaking
 736          * things by calling exit() directly, we have to reset the callbacks
 737          * explicitly to make this work as intended.
 738          */
 739         on_exit_reset();
 740
 741         /*
 742          * Note we do exit(2) not exit(0).      This is to force the postmaster into a
 743          * system reset cycle if some idiot DBA sends a manual SIGQUIT to a random
 744          * backend.  This is necessary precisely because we don't clean up our
 745          * shared memory state.  (The "dead man switch" mechanism in pmsignal.c
 746          * should ensure the postmaster sees this as a crash, too, but no harm
 747          * in being doubly sure.)
 748          */
 749         exit(2);
 750 }
 751
 752 /* SIGUSR2: set flag to do a last cycle and shut down afterwards */
 753 static void
 754 WalSndLastCycleHandler(SIGNAL_ARGS)
 755 {
 756         ready_to_stop = true;
 757 }
 758
 759 /* Set up signal handlers */
 760 void
 761 WalSndSignals(void)
 762 {
 763         /* Set up signal handlers */
 764         pqsignal(SIGHUP, WalSndSigHupHandler);  /* set flag to read config file */
 765         pqsignal(SIGINT, SIG_IGN);      /* not used */
 766         pqsignal(SIGTERM, WalSndShutdownHandler);       /* request shutdown */
 767         pqsignal(SIGQUIT, WalSndQuickDieHandler);       /* hard crash time */
 768         pqsignal(SIGALRM, SIG_IGN);
 769         pqsignal(SIGPIPE, SIG_IGN);
 770         pqsignal(SIGUSR1, SIG_IGN);     /* not used */
 771         pqsignal(SIGUSR2, WalSndLastCycleHandler);      /* request a last cycle and shutdown */
 772
 773         /* Reset some signals that are accepted by postmaster but not here */
 774         pqsignal(SIGCHLD, SIG_DFL);
 775         pqsignal(SIGTTIN, SIG_DFL);
 776         pqsignal(SIGTTOU, SIG_DFL);
 777         pqsignal(SIGCONT, SIG_DFL);
 778         pqsignal(SIGWINCH, SIG_DFL);
 779 }
 780
 781 /* Report shared-memory space needed by WalSndShmemInit */
 782 Size
 783 WalSndShmemSize(void)
 784 {
 785         Size size = 0;
 786
 787         size = offsetof(WalSndCtlData, walsnds);
 788         size = add_size(size, mul_size(MaxWalSenders, sizeof(WalSnd)));
 789
 790         return size;
 791 }
 792
 793 /* Allocate and initialize walsender-related shared memory */
 794 void
 795 WalSndShmemInit(void)
 796 {
 797         bool    found;
 798         int             i;
 799
 800         WalSndCtl = (WalSndCtlData *)
 801                 ShmemInitStruct("Wal Sender Ctl", WalSndShmemSize(), &found);
 802
 803         if (WalSndCtl == NULL)
 804                 ereport(FATAL,
 805                                 (errcode(ERRCODE_OUT_OF_MEMORY),
 806                                  errmsg("not enough shared memory for walsender")));
 807         if (found)
 808                 return;                                 /* already initialized */
 809
 810         /* Initialize the data structures */
 811         MemSet(WalSndCtl, 0, WalSndShmemSize());
 812
 813         for (i = 0; i < MaxWalSenders; i++)
 814         {
 815                 WalSnd  *walsnd = &WalSndCtl->walsnds[i];
 816                 SpinLockInit(&walsnd->mutex);
 817         }
 818 }
 819
 820 /*
 821  * Returns the oldest Send position among walsenders. Or InvalidXLogRecPtr
 822  * if none.
 823  */
 824 XLogRecPtr
 825 GetOldestWALSendPointer(void)
 826 {
 827         XLogRecPtr oldest = {0, 0};
 828         int             i;
 829         bool    found = false;
 830
 831         for (i = 0; i < MaxWalSenders; i++)
 832         {
 833                 /* use volatile pointer to prevent code rearrangement */
 834                 volatile WalSnd *walsnd = &WalSndCtl->walsnds[i];
 835                 XLogRecPtr recptr;
 836
 837                 if (walsnd->pid == 0)
 838                         continue;
 839
 840                 SpinLockAcquire(&walsnd->mutex);
 841                 recptr = walsnd->sentPtr;
 842                 SpinLockRelease(&walsnd->mutex);
 843
 844                 if (recptr.xlogid == 0 && recptr.xrecoff == 0)
 845                         continue;
 846
 847                 if (!found || XLByteLT(recptr, oldest))
 848                         oldest = recptr;
 849                 found = true;
 850         }
 851         return oldest;
 852 }