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 1.32 2010/09/15 06:51:19 heikki Exp $
  32  *
  33  *-------------------------------------------------------------------------
  34  */
  35 #include "postgres.h"
  36
  37 #include <signal.h>
  38 #include <unistd.h>
  39
  40 #include "access/xlog_internal.h"
  41 #include "catalog/pg_type.h"
  42 #include "libpq/libpq.h"
  43 #include "libpq/pqformat.h"
  44 #include "libpq/pqsignal.h"
  45 #include "miscadmin.h"
  46 #include "replication/walprotocol.h"
  47 #include "replication/walsender.h"
  48 #include "storage/fd.h"
  49 #include "storage/ipc.h"
  50 #include "storage/pmsignal.h"
  51 #include "tcop/tcopprot.h"
  52 #include "utils/guc.h"
  53 #include "utils/memutils.h"
  54 #include "utils/ps_status.h"
  55
  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 /*
  71  * These variables are used similarly to openLogFile/Id/Seg/Off,
  72  * but for walsender to read the XLOG.
  73  */
  74 static int      sendFile = -1;
  75 static uint32 sendId = 0;
  76 static uint32 sendSeg = 0;
  77 static uint32 sendOff = 0;
  78
  79 /*
  80  * How far have we sent WAL already? This is also advertised in
  81  * MyWalSnd->sentPtr.  (Actually, this is the next WAL location to send.)
  82  */
  83 static XLogRecPtr sentPtr = {0, 0};
  84
  85 /* Flags set by signal handlers for later service in main loop */
  86 static volatile sig_atomic_t got_SIGHUP = false;
  87 static volatile sig_atomic_t shutdown_requested = false;
  88 static volatile sig_atomic_t ready_to_stop = false;
  89
  90 /* Signal handlers */
  91 static void WalSndSigHupHandler(SIGNAL_ARGS);
  92 static void WalSndShutdownHandler(SIGNAL_ARGS);
  93 static void WalSndQuickDieHandler(SIGNAL_ARGS);
  94 static void WalSndXLogSendHandler(SIGNAL_ARGS);
  95 static void WalSndLastCycleHandler(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(char *msgbuf, bool *caughtup);
 104 static void CheckClosedConnection(void);
 105
 106
 107 /* Main entry point for walsender process */
 108 int
 109 WalSenderMain(void)
 110 {
 111         MemoryContext walsnd_context;
 112
 113         if (RecoveryInProgress())
 114                 ereport(FATAL,
 115                                 (errcode(ERRCODE_CANNOT_CONNECT_NOW),
 116                                  errmsg("recovery is still in progress, can't accept WAL streaming connections")));
 117
 118         /* Create a per-walsender data structure in shared memory */
 119         InitWalSnd();
 120
 121         /*
 122          * Create a memory context that we will do all our work in.  We do this so
 123          * that we can reset the context during error recovery and thereby avoid
 124          * possible memory leaks.  Formerly this code just ran in
 125          * TopMemoryContext, but resetting that would be a really bad idea.
 126          *
 127          * XXX: we don't actually attempt error recovery in walsender, we just
 128          * close the connection and exit.
 129          */
 130         walsnd_context = AllocSetContextCreate(TopMemoryContext,
 131                                                                                    "Wal Sender",
 132                                                                                    ALLOCSET_DEFAULT_MINSIZE,
 133                                                                                    ALLOCSET_DEFAULT_INITSIZE,
 134                                                                                    ALLOCSET_DEFAULT_MAXSIZE);
 135         MemoryContextSwitchTo(walsnd_context);
 136
 137         /* Unblock signals (they were blocked when the postmaster forked us) */
 138         PG_SETMASK(&UnBlockSig);
 139
 140         /* Tell the standby that walsender is ready for receiving commands */
 141         ReadyForQuery(DestRemote);
 142
 143         /* Handle handshake messages before streaming */
 144         WalSndHandshake();
 145
 146         /* Initialize shared memory status */
 147         {
 148                 /* use volatile pointer to prevent code rearrangement */
 149                 volatile WalSnd *walsnd = MyWalSnd;
 150
 151                 SpinLockAcquire(&walsnd->mutex);
 152                 walsnd->sentPtr = sentPtr;
 153                 SpinLockRelease(&walsnd->mutex);
 154         }
 155
 156         /* Main loop of walsender */
 157         return WalSndLoop();
 158 }
 159
 160 /*
 161  * Execute commands from walreceiver, until we enter streaming mode.
 162  */
 163 static void
 164 WalSndHandshake(void)
 165 {
 166         StringInfoData input_message;
 167         bool            replication_started = false;
 168
 169         initStringInfo(&input_message);
 170
 171         while (!replication_started)
 172         {
 173                 int                     firstchar;
 174
 175                 /* Wait for a command to arrive */
 176                 firstchar = pq_getbyte();
 177
 178                 /*
 179                  * Emergency bailout if postmaster has died.  This is to avoid the
 180                  * necessity for manual cleanup of all postmaster children.
 181                  */
 182                 if (!PostmasterIsAlive(true))
 183                         exit(1);
 184
 185                 /*
 186                  * Check for any other interesting events that happened while we
 187                  * slept.
 188                  */
 189                 if (got_SIGHUP)
 190                 {
 191                         got_SIGHUP = false;
 192                         ProcessConfigFile(PGC_SIGHUP);
 193                 }
 194
 195                 if (firstchar != EOF)
 196                 {
 197                         /*
 198                          * Read the message contents. This is expected to be done without
 199                          * blocking because we've been able to get message type code.
 200                          */
 201                         if (pq_getmessage(&input_message, 0))
 202                                 firstchar = EOF;        /* suitable message already logged */
 203                 }
 204
 205                 /* Handle the very limited subset of commands expected in this phase */
 206                 switch (firstchar)
 207                 {
 208                         case 'Q':                       /* Query message */
 209                                 {
 210                                         const char *query_string;
 211                                         XLogRecPtr      recptr;
 212
 213                                         query_string = pq_getmsgstring(&input_message);
 214                                         pq_getmsgend(&input_message);
 215
 216                                         if (strcmp(query_string, "IDENTIFY_SYSTEM") == 0)
 217                                         {
 218                                                 StringInfoData buf;
 219                                                 char            sysid[32];
 220                                                 char            tli[11];
 221
 222                                                 /*
 223                                                  * Reply with a result set with one row, two columns.
 224                                                  * First col is system ID, and second is timeline ID
 225                                                  */
 226
 227                                                 snprintf(sysid, sizeof(sysid), UINT64_FORMAT,
 228                                                                  GetSystemIdentifier());
 229                                                 snprintf(tli, sizeof(tli), "%u", ThisTimeLineID);
 230
 231                                                 /* Send a RowDescription message */
 232                                                 pq_beginmessage(&buf, 'T');
 233                                                 pq_sendint(&buf, 2, 2); /* 2 fields */
 234
 235                                                 /* first field */
 236                                                 pq_sendstring(&buf, "systemid");                /* col name */
 237                                                 pq_sendint(&buf, 0, 4); /* table oid */
 238                                                 pq_sendint(&buf, 0, 2); /* attnum */
 239                                                 pq_sendint(&buf, TEXTOID, 4);   /* type oid */
 240                                                 pq_sendint(&buf, -1, 2);                /* typlen */
 241                                                 pq_sendint(&buf, 0, 4); /* typmod */
 242                                                 pq_sendint(&buf, 0, 2); /* format code */
 243
 244                                                 /* second field */
 245                                                 pq_sendstring(&buf, "timeline");                /* col name */
 246                                                 pq_sendint(&buf, 0, 4); /* table oid */
 247                                                 pq_sendint(&buf, 0, 2); /* attnum */
 248                                                 pq_sendint(&buf, INT4OID, 4);   /* type oid */
 249                                                 pq_sendint(&buf, 4, 2); /* typlen */
 250                                                 pq_sendint(&buf, 0, 4); /* typmod */
 251                                                 pq_sendint(&buf, 0, 2); /* format code */
 252                                                 pq_endmessage(&buf);
 253
 254                                                 /* Send a DataRow message */
 255                                                 pq_beginmessage(&buf, 'D');
 256                                                 pq_sendint(&buf, 2, 2); /* # of columns */
 257                                                 pq_sendint(&buf, strlen(sysid), 4);             /* col1 len */
 258                                                 pq_sendbytes(&buf, (char *) &sysid, strlen(sysid));
 259                                                 pq_sendint(&buf, strlen(tli), 4);               /* col2 len */
 260                                                 pq_sendbytes(&buf, (char *) tli, strlen(tli));
 261                                                 pq_endmessage(&buf);
 262
 263                                                 /* Send CommandComplete and ReadyForQuery messages */
 264                                                 EndCommand("SELECT", DestRemote);
 265                                                 ReadyForQuery(DestRemote);
 266                                                 /* ReadyForQuery did pq_flush for us */
 267                                         }
 268                                         else if (sscanf(query_string, "START_REPLICATION %X/%X",
 269                                                                         &recptr.xlogid, &recptr.xrecoff) == 2)
 270                                         {
 271                                                 StringInfoData buf;
 272
 273                                                 /*
 274                                                  * Check that we're logging enough information in the
 275                                                  * WAL for log-shipping.
 276                                                  *
 277                                                  * NOTE: This only checks the current value of
 278                                                  * wal_level. Even if the current setting is not
 279                                                  * 'minimal', there can be old WAL in the pg_xlog
 280                                                  * directory that was created with 'minimal'. So this
 281                                                  * is not bulletproof, the purpose is just to give a
 282                                                  * user-friendly error message that hints how to
 283                                                  * configure the system correctly.
 284                                                  */
 285                                                 if (wal_level == WAL_LEVEL_MINIMAL)
 286                                                         ereport(FATAL,
 287                                                                         (errcode(ERRCODE_CANNOT_CONNECT_NOW),
 288                                                                          errmsg("standby connections not allowed because wal_level=minimal")));
 289
 290                                                 /* Send a CopyBothResponse message, and start streaming */
 291                                                 pq_beginmessage(&buf, 'W');
 292                                                 pq_sendbyte(&buf, 0);
 293                                                 pq_sendint(&buf, 0, 2);
 294                                                 pq_endmessage(&buf);
 295                                                 pq_flush();
 296
 297                                                 /*
 298                                                  * Initialize position to the received one, then the
 299                                                  * xlog records begin to be shipped from that position
 300                                                  */
 301                                                 sentPtr = recptr;
 302
 303                                                 /* break out of the loop */
 304                                                 replication_started = true;
 305                                         }
 306                                         else
 307                                         {
 308                                                 ereport(FATAL,
 309                                                                 (errcode(ERRCODE_PROTOCOL_VIOLATION),
 310                                                                  errmsg("invalid standby query string: %s", query_string)));
 311                                         }
 312                                         break;
 313                                 }
 314
 315                         case 'X':
 316                                 /* standby is closing the connection */
 317                                 proc_exit(0);
 318
 319                         case EOF:
 320                                 /* standby disconnected unexpectedly */
 321                                 ereport(COMMERROR,
 322                                                 (errcode(ERRCODE_PROTOCOL_VIOLATION),
 323                                                  errmsg("unexpected EOF on standby connection")));
 324                                 proc_exit(0);
 325
 326                         default:
 327                                 ereport(FATAL,
 328                                                 (errcode(ERRCODE_PROTOCOL_VIOLATION),
 329                                                  errmsg("invalid standby handshake message type %d", firstchar)));
 330                 }
 331         }
 332 }
 333
 334 /*
 335  * Check if the remote end has closed the connection.
 336  */
 337 static void
 338 CheckClosedConnection(void)
 339 {
 340         unsigned char firstchar;
 341         int                     r;
 342
 343         r = pq_getbyte_if_available(&firstchar);
 344         if (r < 0)
 345         {
 346                 /* unexpected error or EOF */
 347                 ereport(COMMERROR,
 348                                 (errcode(ERRCODE_PROTOCOL_VIOLATION),
 349                                  errmsg("unexpected EOF on standby connection")));
 350                 proc_exit(0);
 351         }
 352         if (r == 0)
 353         {
 354                 /* no data available without blocking */
 355                 return;
 356         }
 357
 358         /* Handle the very limited subset of commands expected in this phase */
 359         switch (firstchar)
 360         {
 361                         /*
 362                          * 'X' means that the standby is closing down the socket.
 363                          */
 364                 case 'X':
 365                         proc_exit(0);
 366
 367                 default:
 368                         ereport(FATAL,
 369                                         (errcode(ERRCODE_PROTOCOL_VIOLATION),
 370                                          errmsg("invalid standby closing message type %d",
 371                                                         firstchar)));
 372         }
 373 }
 374
 375 /* Main loop of walsender process */
 376 static int
 377 WalSndLoop(void)
 378 {
 379         char       *output_message;
 380         bool            caughtup = false;
 381
 382         /*
 383          * Allocate buffer that will be used for each output message.  We do this
 384          * just once to reduce palloc overhead.  The buffer must be made large
 385          * enough for maximum-sized messages.
 386          */
 387         output_message = palloc(1 + sizeof(WalDataMessageHeader) + MAX_SEND_SIZE);
 388
 389         /* Loop forever, unless we get an error */
 390         for (;;)
 391         {
 392                 /*
 393                  * Emergency bailout if postmaster has died.  This is to avoid the
 394                  * necessity for manual cleanup of all postmaster children.
 395                  */
 396                 if (!PostmasterIsAlive(true))
 397                         exit(1);
 398
 399                 /* Process any requests or signals received recently */
 400                 if (got_SIGHUP)
 401                 {
 402                         got_SIGHUP = false;
 403                         ProcessConfigFile(PGC_SIGHUP);
 404                 }
 405
 406                 /*
 407                  * When SIGUSR2 arrives, we send all outstanding logs up to the
 408                  * shutdown checkpoint record (i.e., the latest record) and exit.
 409                  */
 410                 if (ready_to_stop)
 411                 {
 412                         if (!XLogSend(output_message, &caughtup))
 413                                 break;
 414                         if (caughtup)
 415                                 shutdown_requested = true;
 416                 }
 417
 418                 /* Normal exit from the walsender is here */
 419                 if (shutdown_requested)
 420                 {
 421                         /* Inform the standby that XLOG streaming was done */
 422                         pq_puttextmessage('C', "COPY 0");
 423                         pq_flush();
 424
 425                         proc_exit(0);
 426                 }
 427
 428                 /*
 429                  * If we had sent all accumulated WAL in last round, nap for the
 430                  * configured time before retrying.
 431                  */
 432                 if (caughtup)
 433                 {
 434                         /*
 435                          * Even if we wrote all the WAL that was available when we started
 436                          * sending, more might have arrived while we were sending this
 437                          * batch. We had the latch set while sending, so we have not
 438                          * received any signals from that time. Let's arm the latch
 439                          * again, and after that check that we're still up-to-date.
 440                          */
 441                         ResetLatch(&MyWalSnd->latch);
 442
 443                         if (!XLogSend(output_message, &caughtup))
 444                                 break;
 445                         if (caughtup && !got_SIGHUP && !ready_to_stop && !shutdown_requested)
 446                         {
 447                                 /*
 448                                  * XXX: We don't really need the periodic wakeups anymore,
 449                                  * WaitLatchOrSocket should reliably wake up as soon as
 450                                  * something interesting happens.
 451                                  */
 452
 453                                 /* Sleep */
 454                                 WaitLatchOrSocket(&MyWalSnd->latch, MyProcPort->sock,
 455                                                                   WalSndDelay * 1000L);
 456                         }
 457
 458                         /* Check if the connection was closed */
 459                         CheckClosedConnection();
 460                 }
 461                 else
 462                 {
 463                         /* Attempt to send the log once every loop */
 464                         if (!XLogSend(output_message, &caughtup))
 465                                 break;
 466                 }
 467         }
 468
 469         /*
 470          * Get here on send failure.  Clean up and exit.
 471          *
 472          * Reset whereToSendOutput to prevent ereport from attempting to send any
 473          * more messages to the standby.
 474          */
 475         if (whereToSendOutput == DestRemote)
 476                 whereToSendOutput = DestNone;
 477
 478         proc_exit(0);
 479         return 1;                                       /* keep the compiler quiet */
 480 }
 481
 482 /* Initialize a per-walsender data structure for this walsender process */
 483 static void
 484 InitWalSnd(void)
 485 {
 486         int                     i;
 487
 488         /*
 489          * WalSndCtl should be set up already (we inherit this by fork() or
 490          * EXEC_BACKEND mechanism from the postmaster).
 491          */
 492         Assert(WalSndCtl != NULL);
 493         Assert(MyWalSnd == NULL);
 494
 495         /*
 496          * Find a free walsender slot and reserve it. If this fails, we must be
 497          * out of WalSnd structures.
 498          */
 499         for (i = 0; i < max_wal_senders; i++)
 500         {
 501                 /* use volatile pointer to prevent code rearrangement */
 502                 volatile WalSnd *walsnd = &WalSndCtl->walsnds[i];
 503
 504                 SpinLockAcquire(&walsnd->mutex);
 505
 506                 if (walsnd->pid != 0)
 507                 {
 508                         SpinLockRelease(&walsnd->mutex);
 509                         continue;
 510                 }
 511                 else
 512                 {
 513                         /*
 514                          * Found a free slot. Reserve it for us.
 515                          */
 516                         walsnd->pid = MyProcPid;
 517                         MemSet(&walsnd->sentPtr, 0, sizeof(XLogRecPtr));
 518                         SpinLockRelease(&walsnd->mutex);
 519                         /* don't need the lock anymore */
 520                         OwnLatch((Latch *) &walsnd->latch);
 521                         MyWalSnd = (WalSnd *) walsnd;
 522
 523                         break;
 524                 }
 525         }
 526         if (MyWalSnd == NULL)
 527                 ereport(FATAL,
 528                                 (errcode(ERRCODE_TOO_MANY_CONNECTIONS),
 529                                  errmsg("number of requested standby connections "
 530                                                 "exceeds max_wal_senders (currently %d)",
 531                                                 max_wal_senders)));
 532
 533         /* Arrange to clean up at walsender exit */
 534         on_shmem_exit(WalSndKill, 0);
 535 }
 536
 537 /* Destroy the per-walsender data structure for this walsender process */
 538 static void
 539 WalSndKill(int code, Datum arg)
 540 {
 541         Assert(MyWalSnd != NULL);
 542
 543         /*
 544          * Mark WalSnd struct no longer in use. Assume that no lock is required
 545          * for this.
 546          */
 547         MyWalSnd->pid = 0;
 548         DisownLatch(&MyWalSnd->latch);
 549
 550         /* WalSnd struct isn't mine anymore */
 551         MyWalSnd = NULL;
 552 }
 553
 554 /*
 555  * Read 'nbytes' bytes from WAL into 'buf', starting at location 'recptr'
 556  *
 557  * XXX probably this should be improved to suck data directly from the
 558  * WAL buffers when possible.
 559  */
 560 static void
 561 XLogRead(char *buf, XLogRecPtr recptr, Size nbytes)
 562 {
 563         XLogRecPtr      startRecPtr = recptr;
 564         char            path[MAXPGPATH];
 565         uint32          lastRemovedLog;
 566         uint32          lastRemovedSeg;
 567         uint32          log;
 568         uint32          seg;
 569
 570         while (nbytes > 0)
 571         {
 572                 uint32          startoff;
 573                 int                     segbytes;
 574                 int                     readbytes;
 575
 576                 startoff = recptr.xrecoff % XLogSegSize;
 577
 578                 if (sendFile < 0 || !XLByteInSeg(recptr, sendId, sendSeg))
 579                 {
 580                         /* Switch to another logfile segment */
 581                         if (sendFile >= 0)
 582                                 close(sendFile);
 583
 584                         XLByteToSeg(recptr, sendId, sendSeg);
 585                         XLogFilePath(path, ThisTimeLineID, sendId, sendSeg);
 586
 587                         sendFile = BasicOpenFile(path, O_RDONLY | PG_BINARY, 0);
 588                         if (sendFile < 0)
 589                         {
 590                                 /*
 591                                  * If the file is not found, assume it's because the standby
 592                                  * asked for a too old WAL segment that has already been
 593                                  * removed or recycled.
 594                                  */
 595                                 if (errno == ENOENT)
 596                                 {
 597                                         char            filename[MAXFNAMELEN];
 598
 599                                         XLogFileName(filename, ThisTimeLineID, sendId, sendSeg);
 600                                         ereport(ERROR,
 601                                                         (errcode_for_file_access(),
 602                                                          errmsg("requested WAL segment %s has already been removed",
 603                                                                         filename)));
 604                                 }
 605                                 else
 606                                         ereport(ERROR,
 607                                                         (errcode_for_file_access(),
 608                                                          errmsg("could not open file \"%s\" (log file %u, segment %u): %m",
 609                                                                         path, sendId, sendSeg)));
 610                         }
 611                         sendOff = 0;
 612                 }
 613
 614                 /* Need to seek in the file? */
 615                 if (sendOff != startoff)
 616                 {
 617                         if (lseek(sendFile, (off_t) startoff, SEEK_SET) < 0)
 618                                 ereport(ERROR,
 619                                                 (errcode_for_file_access(),
 620                                                  errmsg("could not seek in log file %u, segment %u to offset %u: %m",
 621                                                                 sendId, sendSeg, startoff)));
 622                         sendOff = startoff;
 623                 }
 624
 625                 /* How many bytes are within this segment? */
 626                 if (nbytes > (XLogSegSize - startoff))
 627                         segbytes = XLogSegSize - startoff;
 628                 else
 629                         segbytes = nbytes;
 630
 631                 readbytes = read(sendFile, buf, segbytes);
 632                 if (readbytes <= 0)
 633                         ereport(ERROR,
 634                                         (errcode_for_file_access(),
 635                         errmsg("could not read from log file %u, segment %u, offset %u, "
 636                                    "length %lu: %m",
 637                                    sendId, sendSeg, sendOff, (unsigned long) segbytes)));
 638
 639                 /* Update state for read */
 640                 XLByteAdvance(recptr, readbytes);
 641
 642                 sendOff += readbytes;
 643                 nbytes -= readbytes;
 644                 buf += readbytes;
 645         }
 646
 647         /*
 648          * After reading into the buffer, check that what we read was valid. We do
 649          * this after reading, because even though the segment was present when we
 650          * opened it, it might get recycled or removed while we read it. The
 651          * read() succeeds in that case, but the data we tried to read might
 652          * already have been overwritten with new WAL records.
 653          */
 654         XLogGetLastRemoved(&lastRemovedLog, &lastRemovedSeg);
 655         XLByteToSeg(startRecPtr, log, seg);
 656         if (log < lastRemovedLog ||
 657                 (log == lastRemovedLog && seg <= lastRemovedSeg))
 658         {
 659                 char            filename[MAXFNAMELEN];
 660
 661                 XLogFileName(filename, ThisTimeLineID, log, seg);
 662                 ereport(ERROR,
 663                                 (errcode_for_file_access(),
 664                                  errmsg("requested WAL segment %s has already been removed",
 665                                                 filename)));
 666         }
 667 }
 668
 669 /*
 670  * Read up to MAX_SEND_SIZE bytes of WAL that's been flushed to disk,
 671  * but not yet sent to the client, and send it.
 672  *
 673  * msgbuf is a work area in which the output message is constructed.  It's
 674  * passed in just so we can avoid re-palloc'ing the buffer on each cycle.
 675  * It must be of size 1 + sizeof(WalDataMessageHeader) + MAX_SEND_SIZE.
 676  *
 677  * If there is no unsent WAL remaining, *caughtup is set to true, otherwise
 678  * *caughtup is set to false.
 679  *
 680  * Returns true if OK, false if trouble.
 681  */
 682 static bool
 683 XLogSend(char *msgbuf, bool *caughtup)
 684 {
 685         XLogRecPtr      SendRqstPtr;
 686         XLogRecPtr      startptr;
 687         XLogRecPtr      endptr;
 688         Size            nbytes;
 689         WalDataMessageHeader msghdr;
 690
 691         /*
 692          * Attempt to send all data that's already been written out and fsync'd to
 693          * disk.  We cannot go further than what's been written out given the
 694          * current implementation of XLogRead().  And in any case it's unsafe to
 695          * send WAL that is not securely down to disk on the master: if the master
 696          * subsequently crashes and restarts, slaves must not have applied any WAL
 697          * that gets lost on the master.
 698          */
 699         SendRqstPtr = GetFlushRecPtr();
 700
 701         /* Quick exit if nothing to do */
 702         if (XLByteLE(SendRqstPtr, sentPtr))
 703         {
 704                 *caughtup = true;
 705                 return true;
 706         }
 707
 708         /*
 709          * Figure out how much to send in one message. If there's no more than
 710          * MAX_SEND_SIZE bytes to send, send everything. Otherwise send
 711          * MAX_SEND_SIZE bytes, but round back to logfile or page boundary.
 712          *
 713          * The rounding is not only for performance reasons. Walreceiver relies on
 714          * the fact that we never split a WAL record across two messages. Since a
 715          * long WAL record is split at page boundary into continuation records,
 716          * page boundary is always a safe cut-off point. We also assume that
 717          * SendRqstPtr never points to the middle of a WAL record.
 718          */
 719         startptr = sentPtr;
 720         if (startptr.xrecoff >= XLogFileSize)
 721         {
 722                 /*
 723                  * crossing a logid boundary, skip the non-existent last log segment
 724                  * in previous logical log file.
 725                  */
 726                 startptr.xlogid += 1;
 727                 startptr.xrecoff = 0;
 728         }
 729
 730         endptr = startptr;
 731         XLByteAdvance(endptr, MAX_SEND_SIZE);
 732         if (endptr.xlogid != startptr.xlogid)
 733         {
 734                 /* Don't cross a logfile boundary within one message */
 735                 Assert(endptr.xlogid == startptr.xlogid + 1);
 736                 endptr.xlogid = startptr.xlogid;
 737                 endptr.xrecoff = XLogFileSize;
 738         }
 739
 740         /* if we went beyond SendRqstPtr, back off */
 741         if (XLByteLE(SendRqstPtr, endptr))
 742         {
 743                 endptr = SendRqstPtr;
 744                 *caughtup = true;
 745         }
 746         else
 747         {
 748                 /* round down to page boundary. */
 749                 endptr.xrecoff -= (endptr.xrecoff % XLOG_BLCKSZ);
 750                 *caughtup = false;
 751         }
 752
 753         nbytes = endptr.xrecoff - startptr.xrecoff;
 754         Assert(nbytes <= MAX_SEND_SIZE);
 755
 756         /*
 757          * OK to read and send the slice.
 758          */
 759         msgbuf[0] = 'w';
 760
 761         /*
 762          * Read the log directly into the output buffer to avoid extra memcpy
 763          * calls.
 764          */
 765         XLogRead(msgbuf + 1 + sizeof(WalDataMessageHeader), startptr, nbytes);
 766
 767         /*
 768          * We fill the message header last so that the send timestamp is taken as
 769          * late as possible.
 770          */
 771         msghdr.dataStart = startptr;
 772         msghdr.walEnd = SendRqstPtr;
 773         msghdr.sendTime = GetCurrentTimestamp();
 774
 775         memcpy(msgbuf + 1, &msghdr, sizeof(WalDataMessageHeader));
 776
 777         pq_putmessage('d', msgbuf, 1 + sizeof(WalDataMessageHeader) + nbytes);
 778
 779         /* Flush pending output to the client */
 780         if (pq_flush())
 781                 return false;
 782
 783         sentPtr = endptr;
 784
 785         /* Update shared memory status */
 786         {
 787                 /* use volatile pointer to prevent code rearrangement */
 788                 volatile WalSnd *walsnd = MyWalSnd;
 789
 790                 SpinLockAcquire(&walsnd->mutex);
 791                 walsnd->sentPtr = sentPtr;
 792                 SpinLockRelease(&walsnd->mutex);
 793         }
 794
 795         /* Report progress of XLOG streaming in PS display */
 796         if (update_process_title)
 797         {
 798                 char            activitymsg[50];
 799
 800                 snprintf(activitymsg, sizeof(activitymsg), "streaming %X/%X",
 801                                  sentPtr.xlogid, sentPtr.xrecoff);
 802                 set_ps_display(activitymsg, false);
 803         }
 804
 805         return true;
 806 }
 807
 808 /* SIGHUP: set flag to re-read config file at next convenient time */
 809 static void
 810 WalSndSigHupHandler(SIGNAL_ARGS)
 811 {
 812         got_SIGHUP = true;
 813         if (MyWalSnd)
 814                 SetLatch(&MyWalSnd->latch);
 815 }
 816
 817 /* SIGTERM: set flag to shut down */
 818 static void
 819 WalSndShutdownHandler(SIGNAL_ARGS)
 820 {
 821         shutdown_requested = true;
 822         if (MyWalSnd)
 823                 SetLatch(&MyWalSnd->latch);
 824 }
 825
 826 /*
 827  * WalSndQuickDieHandler() occurs when signalled SIGQUIT by the postmaster.
 828  *
 829  * Some backend has bought the farm,
 830  * so we need to stop what we're doing and exit.
 831  */
 832 static void
 833 WalSndQuickDieHandler(SIGNAL_ARGS)
 834 {
 835         PG_SETMASK(&BlockSig);
 836
 837         /*
 838          * We DO NOT want to run proc_exit() callbacks -- we're here because
 839          * shared memory may be corrupted, so we don't want to try to clean up our
 840          * transaction.  Just nail the windows shut and get out of town.  Now that
 841          * there's an atexit callback to prevent third-party code from breaking
 842          * things by calling exit() directly, we have to reset the callbacks
 843          * explicitly to make this work as intended.
 844          */
 845         on_exit_reset();
 846
 847         /*
 848          * Note we do exit(2) not exit(0).      This is to force the postmaster into a
 849          * system reset cycle if some idiot DBA sends a manual SIGQUIT to a random
 850          * backend.  This is necessary precisely because we don't clean up our
 851          * shared memory state.  (The "dead man switch" mechanism in pmsignal.c
 852          * should ensure the postmaster sees this as a crash, too, but no harm in
 853          * being doubly sure.)
 854          */
 855         exit(2);
 856 }
 857
 858 /* SIGUSR1: set flag to send WAL records */
 859 static void
 860 WalSndXLogSendHandler(SIGNAL_ARGS)
 861 {
 862         latch_sigusr1_handler();
 863 }
 864
 865 /* SIGUSR2: set flag to do a last cycle and shut down afterwards */
 866 static void
 867 WalSndLastCycleHandler(SIGNAL_ARGS)
 868 {
 869         ready_to_stop = true;
 870         if (MyWalSnd)
 871                 SetLatch(&MyWalSnd->latch);
 872 }
 873
 874 /* Set up signal handlers */
 875 void
 876 WalSndSignals(void)
 877 {
 878         /* Set up signal handlers */
 879         pqsignal(SIGHUP, WalSndSigHupHandler);          /* set flag to read config
 880                                                                                                  * file */
 881         pqsignal(SIGINT, SIG_IGN);      /* not used */
 882         pqsignal(SIGTERM, WalSndShutdownHandler);       /* request shutdown */
 883         pqsignal(SIGQUIT, WalSndQuickDieHandler);       /* hard crash time */
 884         pqsignal(SIGALRM, SIG_IGN);
 885         pqsignal(SIGPIPE, SIG_IGN);
 886         pqsignal(SIGUSR1, WalSndXLogSendHandler);       /* request WAL sending */
 887         pqsignal(SIGUSR2, WalSndLastCycleHandler);      /* request a last cycle and
 888                                                                                                  * shutdown */
 889
 890         /* Reset some signals that are accepted by postmaster but not here */
 891         pqsignal(SIGCHLD, SIG_DFL);
 892         pqsignal(SIGTTIN, SIG_DFL);
 893         pqsignal(SIGTTOU, SIG_DFL);
 894         pqsignal(SIGCONT, SIG_DFL);
 895         pqsignal(SIGWINCH, SIG_DFL);
 896 }
 897
 898 /* Report shared-memory space needed by WalSndShmemInit */
 899 Size
 900 WalSndShmemSize(void)
 901 {
 902         Size            size = 0;
 903
 904         size = offsetof(WalSndCtlData, walsnds);
 905         size = add_size(size, mul_size(max_wal_senders, sizeof(WalSnd)));
 906
 907         return size;
 908 }
 909
 910 /* Allocate and initialize walsender-related shared memory */
 911 void
 912 WalSndShmemInit(void)
 913 {
 914         bool            found;
 915         int                     i;
 916
 917         WalSndCtl = (WalSndCtlData *)
 918                 ShmemInitStruct("Wal Sender Ctl", WalSndShmemSize(), &found);
 919
 920         if (!found)
 921         {
 922                 /* First time through, so initialize */
 923                 MemSet(WalSndCtl, 0, WalSndShmemSize());
 924
 925                 for (i = 0; i < max_wal_senders; i++)
 926                 {
 927                         WalSnd     *walsnd = &WalSndCtl->walsnds[i];
 928
 929                         SpinLockInit(&walsnd->mutex);
 930                         InitSharedLatch(&walsnd->latch);
 931                 }
 932         }
 933 }
 934
 935 /* Wake up all walsenders */
 936 void
 937 WalSndWakeup(void)
 938 {
 939         int             i;
 940
 941         for (i = 0; i < max_wal_senders; i++)
 942                 SetLatch(&WalSndCtl->walsnds[i].latch);
 943 }
 944
 945 /*
 946  * This isn't currently used for anything. Monitoring tools might be
 947  * interested in the future, and we'll need something like this in the
 948  * future for synchronous replication.
 949  */
 950 #ifdef NOT_USED
 951 /*
 952  * Returns the oldest Send position among walsenders. Or InvalidXLogRecPtr
 953  * if none.
 954  */
 955 XLogRecPtr
 956 GetOldestWALSendPointer(void)
 957 {
 958         XLogRecPtr      oldest = {0, 0};
 959         int                     i;
 960         bool            found = false;
 961
 962         for (i = 0; i < max_wal_senders; i++)
 963         {
 964                 /* use volatile pointer to prevent code rearrangement */
 965                 volatile WalSnd *walsnd = &WalSndCtl->walsnds[i];
 966                 XLogRecPtr      recptr;
 967
 968                 if (walsnd->pid == 0)
 969                         continue;
 970
 971                 SpinLockAcquire(&walsnd->mutex);
 972                 recptr = walsnd->sentPtr;
 973                 SpinLockRelease(&walsnd->mutex);
 974
 975                 if (recptr.xlogid == 0 && recptr.xrecoff == 0)
 976                         continue;
 977
 978                 if (!found || XLByteLT(recptr, oldest))
 979                         oldest = recptr;
 980                 found = true;
 981         }
 982         return oldest;
 983 }
 984
 985 #endif