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  * 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 1.14 2010/04/01 00:43:29 rhaas 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                     max_wal_senders = 0;    /* the maximum number of concurrent walsenders */
  68 int                     WalSndDelay = 200;      /* max sleep time between some actions */
  69
  70 #define NAPTIME_PER_CYCLE 100000L       /* 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         if (RecoveryInProgress())
 123                 ereport(FATAL,
 124                                 (errcode(ERRCODE_CANNOT_CONNECT_NOW),
 125                                  errmsg("recovery is still in progress, can't accept WAL streaming connections")));
 126
 127         /* Create a per-walsender data structure in shared memory */
 128         InitWalSnd();
 129
 130         /*
 131          * Create a memory context that we will do all our work in.  We do this so
 132          * that we can reset the context during error recovery and thereby avoid
 133          * possible memory leaks.  Formerly this code just ran in
 134          * TopMemoryContext, but resetting that would be a really bad idea.
 135          *
 136          * XXX: we don't actually attempt error recovery in walsender, we just
 137          * close the connection and exit.
 138          */
 139         walsnd_context = AllocSetContextCreate(TopMemoryContext,
 140                                                                                    "Wal Sender",
 141                                                                                    ALLOCSET_DEFAULT_MINSIZE,
 142                                                                                    ALLOCSET_DEFAULT_INITSIZE,
 143                                                                                    ALLOCSET_DEFAULT_MAXSIZE);
 144         MemoryContextSwitchTo(walsnd_context);
 145
 146         /* Unblock signals (they were blocked when the postmaster forked us) */
 147         PG_SETMASK(&UnBlockSig);
 148
 149         /* Tell the standby that walsender is ready for receiving commands */
 150         ReadyForQuery(DestRemote);
 151
 152         /* Handle handshake messages before streaming */
 153         WalSndHandshake();
 154
 155         /* Main loop of walsender */
 156         return WalSndLoop();
 157 }
 158
 159 static void
 160 WalSndHandshake(void)
 161 {
 162         StringInfoData input_message;
 163         bool            replication_started = false;
 164
 165         initStringInfo(&input_message);
 166
 167         while (!replication_started)
 168         {
 169                 int                     firstchar;
 170
 171                 /* Wait for a command to arrive */
 172                 firstchar = pq_getbyte();
 173
 174                 /*
 175                  * Check for any other interesting events that happened while we
 176                  * slept.
 177                  */
 178                 if (got_SIGHUP)
 179                 {
 180                         got_SIGHUP = false;
 181                         ProcessConfigFile(PGC_SIGHUP);
 182                 }
 183
 184                 if (firstchar != EOF)
 185                 {
 186                         /*
 187                          * Read the message contents. This is expected to be done without
 188                          * blocking because we've been able to get message type code.
 189                          */
 190                         if (pq_getmessage(&input_message, 0))
 191                                 firstchar = EOF;        /* suitable message already logged */
 192                 }
 193
 194                 /* Handle the very limited subset of commands expected in this phase */
 195                 switch (firstchar)
 196                 {
 197                         case 'Q':                       /* Query message */
 198                                 {
 199                                         const char *query_string;
 200                                         XLogRecPtr      recptr;
 201
 202                                         query_string = pq_getmsgstring(&input_message);
 203                                         pq_getmsgend(&input_message);
 204
 205                                         if (strcmp(query_string, "IDENTIFY_SYSTEM") == 0)
 206                                         {
 207                                                 StringInfoData buf;
 208                                                 char            sysid[32];
 209                                                 char            tli[11];
 210
 211                                                 /*
 212                                                  * Reply with a result set with one row, two columns.
 213                                                  * First col is system ID, and second if timeline ID
 214                                                  */
 215
 216                                                 snprintf(sysid, sizeof(sysid), UINT64_FORMAT,
 217                                                                  GetSystemIdentifier());
 218                                                 snprintf(tli, sizeof(tli), "%u", ThisTimeLineID);
 219
 220                                                 /* Send a RowDescription message */
 221                                                 pq_beginmessage(&buf, 'T');
 222                                                 pq_sendint(&buf, 2, 2); /* 2 fields */
 223
 224                                                 /* first field */
 225                                                 pq_sendstring(&buf, "systemid");                /* col name */
 226                                                 pq_sendint(&buf, 0, 4); /* table oid */
 227                                                 pq_sendint(&buf, 0, 2); /* attnum */
 228                                                 pq_sendint(&buf, TEXTOID, 4);   /* type oid */
 229                                                 pq_sendint(&buf, -1, 2);                /* typlen */
 230                                                 pq_sendint(&buf, 0, 4); /* typmod */
 231                                                 pq_sendint(&buf, 0, 2); /* format code */
 232
 233                                                 /* second field */
 234                                                 pq_sendstring(&buf, "timeline");                /* col name */
 235                                                 pq_sendint(&buf, 0, 4); /* table oid */
 236                                                 pq_sendint(&buf, 0, 2); /* attnum */
 237                                                 pq_sendint(&buf, INT4OID, 4);   /* type oid */
 238                                                 pq_sendint(&buf, 4, 2); /* typlen */
 239                                                 pq_sendint(&buf, 0, 4); /* typmod */
 240                                                 pq_sendint(&buf, 0, 2); /* format code */
 241                                                 pq_endmessage(&buf);
 242
 243                                                 /* Send a DataRow message */
 244                                                 pq_beginmessage(&buf, 'D');
 245                                                 pq_sendint(&buf, 2, 2); /* # of columns */
 246                                                 pq_sendint(&buf, strlen(sysid), 4);             /* col1 len */
 247                                                 pq_sendbytes(&buf, (char *) &sysid, strlen(sysid));
 248                                                 pq_sendint(&buf, strlen(tli), 4);               /* col2 len */
 249                                                 pq_sendbytes(&buf, (char *) tli, strlen(tli));
 250                                                 pq_endmessage(&buf);
 251
 252                                                 /* Send CommandComplete and ReadyForQuery messages */
 253                                                 EndCommand("SELECT", DestRemote);
 254                                                 ReadyForQuery(DestRemote);
 255                                         }
 256                                         else if (sscanf(query_string, "START_REPLICATION %X/%X",
 257                                                                         &recptr.xlogid, &recptr.xrecoff) == 2)
 258                                         {
 259                                                 StringInfoData buf;
 260
 261                                                 /* Send a CopyOutResponse message, and start streaming */
 262                                                 pq_beginmessage(&buf, 'H');
 263                                                 pq_sendbyte(&buf, 0);
 264                                                 pq_sendint(&buf, 0, 2);
 265                                                 pq_endmessage(&buf);
 266                                                 pq_flush();
 267
 268                                                 /*
 269                                                  * Initialize position to the received one, then the
 270                                                  * xlog records begin to be shipped from that position
 271                                                  */
 272                                                 sentPtr = recptr;
 273
 274                                                 /* break out of the loop */
 275                                                 replication_started = true;
 276                                         }
 277                                         else
 278                                         {
 279                                                 ereport(FATAL,
 280                                                                 (errcode(ERRCODE_PROTOCOL_VIOLATION),
 281                                                                  errmsg("invalid standby query string: %s", query_string)));
 282                                         }
 283                                         break;
 284                                 }
 285
 286                         case 'X':
 287                                 /* standby is closing the connection */
 288                                 proc_exit(0);
 289
 290                         case EOF:
 291                                 /* standby disconnected unexpectedly */
 292                                 ereport(COMMERROR,
 293                                                 (errcode(ERRCODE_PROTOCOL_VIOLATION),
 294                                                  errmsg("unexpected EOF on standby connection")));
 295                                 proc_exit(0);
 296
 297                         default:
 298                                 ereport(FATAL,
 299                                                 (errcode(ERRCODE_PROTOCOL_VIOLATION),
 300                                                  errmsg("invalid standby handshake message type %d", firstchar)));
 301                 }
 302         }
 303 }
 304
 305 /*
 306  * Check if the remote end has closed the connection.
 307  */
 308 static void
 309 CheckClosedConnection(void)
 310 {
 311         unsigned char firstchar;
 312         int                     r;
 313
 314         r = pq_getbyte_if_available(&firstchar);
 315         if (r < 0)
 316         {
 317                 /* unexpected error or EOF */
 318                 ereport(COMMERROR,
 319                                 (errcode(ERRCODE_PROTOCOL_VIOLATION),
 320                                  errmsg("unexpected EOF on standby connection")));
 321                 proc_exit(0);
 322         }
 323         if (r == 0)
 324         {
 325                 /* no data available without blocking */
 326                 return;
 327         }
 328
 329         /* Handle the very limited subset of commands expected in this phase */
 330         switch (firstchar)
 331         {
 332                         /*
 333                          * 'X' means that the standby is closing down the socket.
 334                          */
 335                 case 'X':
 336                         proc_exit(0);
 337
 338                 default:
 339                         ereport(FATAL,
 340                                         (errcode(ERRCODE_PROTOCOL_VIOLATION),
 341                                          errmsg("invalid standby closing message type %d",
 342                                                         firstchar)));
 343         }
 344 }
 345
 346 /* Main loop of walsender process */
 347 static int
 348 WalSndLoop(void)
 349 {
 350         StringInfoData output_message;
 351
 352         initStringInfo(&output_message);
 353
 354         /* Loop forever */
 355         for (;;)
 356         {
 357                 long    remain;         /* remaining time (us) */
 358
 359                 /*
 360                  * Emergency bailout if postmaster has died.  This is to avoid the
 361                  * necessity for manual cleanup of all postmaster children.
 362                  */
 363                 if (!PostmasterIsAlive(true))
 364                         exit(1);
 365                 /* Process any requests or signals received recently */
 366                 if (got_SIGHUP)
 367                 {
 368                         got_SIGHUP = false;
 369                         ProcessConfigFile(PGC_SIGHUP);
 370                 }
 371
 372                 /*
 373                  * When SIGUSR2 arrives, we send all outstanding logs up to the
 374                  * shutdown checkpoint record (i.e., the latest record) and exit.
 375                  */
 376                 if (ready_to_stop)
 377                 {
 378                         XLogSend(&output_message);
 379                         shutdown_requested = true;
 380                 }
 381
 382                 /* Normal exit from the walsender is here */
 383                 if (shutdown_requested)
 384                 {
 385                         /* Inform the standby that XLOG streaming was done */
 386                         pq_puttextmessage('C', "COPY 0");
 387                         pq_flush();
 388
 389                         proc_exit(0);
 390                 }
 391
 392                 /*
 393                  * Nap for the configured time or until a message arrives.
 394                  *
 395                  * On some platforms, signals won't interrupt the sleep.  To ensure we
 396                  * respond reasonably promptly when someone signals us, break down the
 397                  * sleep into NAPTIME_PER_CYCLE increments, and check for
 398                  * interrupts after each nap.
 399                  */
 400                 remain = WalSndDelay * 1000L;
 401                 while (remain > 0)
 402                 {
 403                         if (got_SIGHUP || shutdown_requested || ready_to_stop)
 404                                 break;
 405
 406                         /*
 407                          * Check to see whether a message from the standby or an interrupt
 408                          * from other processes has arrived.
 409                          */
 410                         pg_usleep(remain > NAPTIME_PER_CYCLE ? NAPTIME_PER_CYCLE : remain);
 411                         CheckClosedConnection();
 412
 413                         remain -= NAPTIME_PER_CYCLE;
 414                 }
 415
 416                 /* Attempt to send the log once every loop */
 417                 if (!XLogSend(&output_message))
 418                         goto eof;
 419         }
 420
 421         /* can't get here because the above loop never exits */
 422         return 1;
 423
 424 eof:
 425
 426         /*
 427          * Reset whereToSendOutput to prevent ereport from attempting to send any
 428          * more messages to the standby.
 429          */
 430         if (whereToSendOutput == DestRemote)
 431                 whereToSendOutput = DestNone;
 432
 433         proc_exit(0);
 434         return 1;                                       /* keep the compiler quiet */
 435 }
 436
 437 /* Initialize a per-walsender data structure for this walsender process */
 438 static void
 439 InitWalSnd(void)
 440 {
 441         /* use volatile pointer to prevent code rearrangement */
 442         int                     i;
 443
 444         /*
 445          * WalSndCtl should be set up already (we inherit this by fork() or
 446          * EXEC_BACKEND mechanism from the postmaster).
 447          */
 448         Assert(WalSndCtl != NULL);
 449         Assert(MyWalSnd == NULL);
 450
 451         /*
 452          * Find a free walsender slot and reserve it. If this fails, we must be
 453          * out of WalSnd structures.
 454          */
 455         for (i = 0; i < max_wal_senders; i++)
 456         {
 457                 volatile WalSnd *walsnd = &WalSndCtl->walsnds[i];
 458
 459                 SpinLockAcquire(&walsnd->mutex);
 460
 461                 if (walsnd->pid != 0)
 462                 {
 463                         SpinLockRelease(&walsnd->mutex);
 464                         continue;
 465                 }
 466                 else
 467                 {
 468                         /* found */
 469                         MyWalSnd = (WalSnd *) walsnd;
 470                         walsnd->pid = MyProcPid;
 471                         MemSet(&MyWalSnd->sentPtr, 0, sizeof(XLogRecPtr));
 472                         SpinLockRelease(&walsnd->mutex);
 473                         break;
 474                 }
 475         }
 476         if (MyWalSnd == NULL)
 477                 ereport(FATAL,
 478                                 (errcode(ERRCODE_TOO_MANY_CONNECTIONS),
 479                                  errmsg("number of requested standby connections "
 480                                         "exceeds max_wal_senders (currently %d)",
 481                                         max_wal_senders)));
 482
 483         /* Arrange to clean up at walsender exit */
 484         on_shmem_exit(WalSndKill, 0);
 485 }
 486
 487 /* Destroy the per-walsender data structure for this walsender process */
 488 static void
 489 WalSndKill(int code, Datum arg)
 490 {
 491         Assert(MyWalSnd != NULL);
 492
 493         /*
 494          * Mark WalSnd struct no longer in use. Assume that no lock is required
 495          * for this.
 496          */
 497         MyWalSnd->pid = 0;
 498
 499         /* WalSnd struct isn't mine anymore */
 500         MyWalSnd = NULL;
 501 }
 502
 503 /*
 504  * Read 'nbytes' bytes from WAL into 'buf', starting at location 'recptr'
 505  */
 506 void
 507 XLogRead(char *buf, XLogRecPtr recptr, Size nbytes)
 508 {
 509         char            path[MAXPGPATH];
 510         uint32          startoff;
 511
 512         while (nbytes > 0)
 513         {
 514                 int                     segbytes;
 515                 int                     readbytes;
 516
 517                 startoff = recptr.xrecoff % XLogSegSize;
 518
 519                 if (sendFile < 0 || !XLByteInSeg(recptr, sendId, sendSeg))
 520                 {
 521                         /* Switch to another logfile segment */
 522                         if (sendFile >= 0)
 523                                 close(sendFile);
 524
 525                         XLByteToSeg(recptr, sendId, sendSeg);
 526                         XLogFilePath(path, ThisTimeLineID, sendId, sendSeg);
 527
 528                         sendFile = BasicOpenFile(path, O_RDONLY | PG_BINARY, 0);
 529                         if (sendFile < 0)
 530                                 ereport(FATAL,  /* XXX: Why FATAL? */
 531                                                 (errcode_for_file_access(),
 532                                                  errmsg("could not open file \"%s\" (log file %u, segment %u): %m",
 533                                                                 path, sendId, sendSeg)));
 534                         sendOff = 0;
 535                 }
 536
 537                 /* Need to seek in the file? */
 538                 if (sendOff != startoff)
 539                 {
 540                         if (lseek(sendFile, (off_t) startoff, SEEK_SET) < 0)
 541                                 ereport(FATAL,
 542                                                 (errcode_for_file_access(),
 543                                                  errmsg("could not seek in log file %u, segment %u to offset %u: %m",
 544                                                                 sendId, sendSeg, startoff)));
 545                         sendOff = startoff;
 546                 }
 547
 548                 /* How many bytes are within this segment? */
 549                 if (nbytes > (XLogSegSize - startoff))
 550                         segbytes = XLogSegSize - startoff;
 551                 else
 552                         segbytes = nbytes;
 553
 554                 readbytes = read(sendFile, buf, segbytes);
 555                 if (readbytes <= 0)
 556                         ereport(FATAL,
 557                                         (errcode_for_file_access(),
 558                         errmsg("could not read from log file %u, segment %u, offset %u, "
 559                                    "length %lu: %m",
 560                                    sendId, sendSeg, sendOff, (unsigned long) segbytes)));
 561
 562                 /* Update state for read */
 563                 XLByteAdvance(recptr, readbytes);
 564
 565                 sendOff += readbytes;
 566                 nbytes -= readbytes;
 567                 buf += readbytes;
 568         }
 569 }
 570
 571 /*
 572  * Read all WAL that's been written (and flushed) since last cycle, and send
 573  * it to client.
 574  *
 575  * Returns true if OK, false if trouble.
 576  */
 577 static bool
 578 XLogSend(StringInfo outMsg)
 579 {
 580         XLogRecPtr      SendRqstPtr;
 581         char            activitymsg[50];
 582
 583         /* use volatile pointer to prevent code rearrangement */
 584         volatile WalSnd *walsnd = MyWalSnd;
 585
 586         /* Attempt to send all records flushed to the disk already */
 587         SendRqstPtr = GetWriteRecPtr();
 588
 589         /* Quick exit if nothing to do */
 590         if (!XLByteLT(sentPtr, SendRqstPtr))
 591                 return true;
 592
 593         /*
 594          * We gather multiple records together by issuing just one XLogRead() of a
 595          * suitable size, and send them as one CopyData message. Repeat until
 596          * we've sent everything we can.
 597          */
 598         while (XLByteLT(sentPtr, SendRqstPtr))
 599         {
 600                 XLogRecPtr      startptr;
 601                 XLogRecPtr      endptr;
 602                 Size            nbytes;
 603
 604                 /*
 605                  * Figure out how much to send in one message. If there's less than
 606                  * MAX_SEND_SIZE bytes to send, send everything. Otherwise send
 607                  * MAX_SEND_SIZE bytes, but round to page boundary.
 608                  *
 609                  * The rounding is not only for performance reasons. Walreceiver
 610                  * relies on the fact that we never split a WAL record across two
 611                  * messages. Since a long WAL record is split at page boundary into
 612                  * continuation records, page boundary is always a safe cut-off point.
 613                  * We also assume that SendRqstPtr never points in the middle of a WAL
 614                  * record.
 615                  */
 616                 startptr = sentPtr;
 617                 if (startptr.xrecoff >= XLogFileSize)
 618                 {
 619                         /*
 620                          * crossing a logid boundary, skip the non-existent last log
 621                          * segment in previous logical log file.
 622                          */
 623                         startptr.xlogid += 1;
 624                         startptr.xrecoff = 0;
 625                 }
 626
 627                 endptr = startptr;
 628                 XLByteAdvance(endptr, MAX_SEND_SIZE);
 629                 /* round down to page boundary. */
 630                 endptr.xrecoff -= (endptr.xrecoff % XLOG_BLCKSZ);
 631                 /* if we went beyond SendRqstPtr, back off */
 632                 if (XLByteLT(SendRqstPtr, endptr))
 633                         endptr = SendRqstPtr;
 634
 635                 /*
 636                  * OK to read and send the slice.
 637                  *
 638                  * We don't need to convert the xlogid/xrecoff from host byte order to
 639                  * network byte order because the both server can be expected to have
 640                  * the same byte order. If they have different byte order, we don't
 641                  * reach here.
 642                  */
 643                 pq_sendbyte(outMsg, 'w');
 644                 pq_sendbytes(outMsg, (char *) &startptr, sizeof(startptr));
 645
 646                 if (endptr.xlogid != startptr.xlogid)
 647                 {
 648                         Assert(endptr.xlogid == startptr.xlogid + 1);
 649                         nbytes = endptr.xrecoff + XLogFileSize - startptr.xrecoff;
 650                 }
 651                 else
 652                         nbytes = endptr.xrecoff - startptr.xrecoff;
 653
 654                 sentPtr = endptr;
 655
 656                 /*
 657                  * Read the log directly into the output buffer to prevent extra
 658                  * memcpy calls.
 659                  */
 660                 enlargeStringInfo(outMsg, nbytes);
 661
 662                 XLogRead(&outMsg->data[outMsg->len], startptr, nbytes);
 663                 outMsg->len += nbytes;
 664                 outMsg->data[outMsg->len] = '\0';
 665
 666                 pq_putmessage('d', outMsg->data, outMsg->len);
 667                 resetStringInfo(outMsg);
 668         }
 669
 670         /* Update shared memory status */
 671         SpinLockAcquire(&walsnd->mutex);
 672         walsnd->sentPtr = sentPtr;
 673         SpinLockRelease(&walsnd->mutex);
 674
 675         /* Flush pending output */
 676         if (pq_flush())
 677                 return false;
 678
 679         /* Report progress of XLOG streaming in PS display */
 680         snprintf(activitymsg, sizeof(activitymsg), "streaming %X/%X",
 681                          sentPtr.xlogid, sentPtr.xrecoff);
 682         set_ps_display(activitymsg, false);
 683
 684         return true;
 685 }
 686
 687 /* SIGHUP: set flag to re-read config file at next convenient time */
 688 static void
 689 WalSndSigHupHandler(SIGNAL_ARGS)
 690 {
 691         got_SIGHUP = true;
 692 }
 693
 694 /* SIGTERM: set flag to shut down */
 695 static void
 696 WalSndShutdownHandler(SIGNAL_ARGS)
 697 {
 698         shutdown_requested = true;
 699 }
 700
 701 /*
 702  * WalSndQuickDieHandler() occurs when signalled SIGQUIT by the postmaster.
 703  *
 704  * Some backend has bought the farm,
 705  * so we need to stop what we're doing and exit.
 706  */
 707 static void
 708 WalSndQuickDieHandler(SIGNAL_ARGS)
 709 {
 710         PG_SETMASK(&BlockSig);
 711
 712         /*
 713          * We DO NOT want to run proc_exit() callbacks -- we're here because
 714          * shared memory may be corrupted, so we don't want to try to clean up our
 715          * transaction.  Just nail the windows shut and get out of town.  Now that
 716          * there's an atexit callback to prevent third-party code from breaking
 717          * things by calling exit() directly, we have to reset the callbacks
 718          * explicitly to make this work as intended.
 719          */
 720         on_exit_reset();
 721
 722         /*
 723          * Note we do exit(2) not exit(0).      This is to force the postmaster into a
 724          * system reset cycle if some idiot DBA sends a manual SIGQUIT to a random
 725          * backend.  This is necessary precisely because we don't clean up our
 726          * shared memory state.  (The "dead man switch" mechanism in pmsignal.c
 727          * should ensure the postmaster sees this as a crash, too, but no harm in
 728          * being doubly sure.)
 729          */
 730         exit(2);
 731 }
 732
 733 /* SIGUSR2: set flag to do a last cycle and shut down afterwards */
 734 static void
 735 WalSndLastCycleHandler(SIGNAL_ARGS)
 736 {
 737         ready_to_stop = true;
 738 }
 739
 740 /* Set up signal handlers */
 741 void
 742 WalSndSignals(void)
 743 {
 744         /* Set up signal handlers */
 745         pqsignal(SIGHUP, WalSndSigHupHandler);          /* set flag to read config
 746                                                                                                  * file */
 747         pqsignal(SIGINT, SIG_IGN);      /* not used */
 748         pqsignal(SIGTERM, WalSndShutdownHandler);       /* request shutdown */
 749         pqsignal(SIGQUIT, WalSndQuickDieHandler);       /* hard crash time */
 750         pqsignal(SIGALRM, SIG_IGN);
 751         pqsignal(SIGPIPE, SIG_IGN);
 752         pqsignal(SIGUSR1, SIG_IGN); /* not used */
 753         pqsignal(SIGUSR2, WalSndLastCycleHandler);      /* request a last cycle and
 754                                                                                                  * shutdown */
 755
 756         /* Reset some signals that are accepted by postmaster but not here */
 757         pqsignal(SIGCHLD, SIG_DFL);
 758         pqsignal(SIGTTIN, SIG_DFL);
 759         pqsignal(SIGTTOU, SIG_DFL);
 760         pqsignal(SIGCONT, SIG_DFL);
 761         pqsignal(SIGWINCH, SIG_DFL);
 762 }
 763
 764 /* Report shared-memory space needed by WalSndShmemInit */
 765 Size
 766 WalSndShmemSize(void)
 767 {
 768         Size            size = 0;
 769
 770         size = offsetof(WalSndCtlData, walsnds);
 771         size = add_size(size, mul_size(max_wal_senders, sizeof(WalSnd)));
 772
 773         return size;
 774 }
 775
 776 /* Allocate and initialize walsender-related shared memory */
 777 void
 778 WalSndShmemInit(void)
 779 {
 780         bool            found;
 781         int                     i;
 782
 783         WalSndCtl = (WalSndCtlData *)
 784                 ShmemInitStruct("Wal Sender Ctl", WalSndShmemSize(), &found);
 785
 786         if (WalSndCtl == NULL)
 787                 ereport(FATAL,
 788                                 (errcode(ERRCODE_OUT_OF_MEMORY),
 789                                  errmsg("not enough shared memory for walsender")));
 790         if (found)
 791                 return;                                 /* already initialized */
 792
 793         /* Initialize the data structures */
 794         MemSet(WalSndCtl, 0, WalSndShmemSize());
 795
 796         for (i = 0; i < max_wal_senders; i++)
 797         {
 798                 WalSnd     *walsnd = &WalSndCtl->walsnds[i];
 799
 800                 SpinLockInit(&walsnd->mutex);
 801         }
 802 }
 803
 804 /*
 805  * Returns the oldest Send position among walsenders. Or InvalidXLogRecPtr
 806  * if none.
 807  */
 808 XLogRecPtr
 809 GetOldestWALSendPointer(void)
 810 {
 811         XLogRecPtr      oldest = {0, 0};
 812         int                     i;
 813         bool            found = false;
 814
 815         for (i = 0; i < max_wal_senders; i++)
 816         {
 817                 /* use volatile pointer to prevent code rearrangement */
 818                 volatile WalSnd *walsnd = &WalSndCtl->walsnds[i];
 819                 XLogRecPtr      recptr;
 820
 821                 if (walsnd->pid == 0)
 822                         continue;
 823
 824                 SpinLockAcquire(&walsnd->mutex);
 825                 recptr = walsnd->sentPtr;
 826                 SpinLockRelease(&walsnd->mutex);
 827
 828                 if (recptr.xlogid == 0 && recptr.xrecoff == 0)
 829                         continue;
 830
 831                 if (!found || XLByteLT(recptr, oldest))
 832                         oldest = recptr;
 833                 found = true;
 834         }
 835         return oldest;
 836 }