do_start->
 pm_pid = start_postmaster();
 if (do_wait){
  print_msg(_("waiting for server to start..."));
  switch (wait_for_postmaster(pm_pid, false)){
   case POSTMASTER_READY:
    print_msg(_(" done\n"));
    print_msg(_("server started\n"));
    break;
   case POSTMASTER_STILL_STARTING:
    print_msg(_(" stopped waiting\n"));
    write_stderr(_("%s: server did not start in time\n"), progname);
    exit(1);
    break;
   case POSTMASTER_FAILED:
    print_msg(_(" stopped waiting\n"));
    write_stderr(_("%s: could not start server\n" "Examine the log output.\n"), progname);
    exit(1);
    break;
  }
 }else
  print_msg(_("server starting\n"));

wait_for_postmaster->
 for (i = 0; i < wait_seconds * WAITS_PER_SEC; i++){
  if ((optlines = readfile(pid_file, &numlines)) != NULL && numlines >= LOCK_FILE_LINE_PM_STATUS){
   pmpid = atol(optlines[LOCK_FILE_LINE_PID - 1]);
   pmstart = atol(optlines[LOCK_FILE_LINE_START_TIME - 1]);
   if (pmstart >= start_time - 2 && pmpid == pm_pid){
    char  *pmstatus = optlines[LOCK_FILE_LINE_PM_STATUS - 1];
    if (strcmp(pmstatus, PM_STATUS_READY) == 0 || strcmp(pmstatus, PM_STATUS_STANDBY) == 0){
     /* postmaster is done starting up */
     free_readfile(optlines);
     return POSTMASTER_READY;
    }
   }
  }
  free_readfile(optlines);
  if (waitpid((pid_t) pm_pid, &exitstatus, WNOHANG) == (pid_t) pm_pid)
   return POSTMASTER_FAILED;
  pg_usleep(USEC_PER_SEC / WAITS_PER_SEC);
 }
 /* out of patience; report that postmaster is still starting up */
 return POSTMASTER_STILL_STARTING;

PostmasterMain->
 pqsignal_no_restart(SIGUSR1, sigusr1_handler); /* message from child process */
 pqsignal_no_restart(SIGCHLD, reaper); /* handle child termination */
 ...
 StartupXLOG();
 ...
 proc_exit(0);//exit函数向主进程发送SIGCHLD信号

reaper->//进程终止或者停止的信号
 AddToDataDirLockFile(LOCK_FILE_LINE_PM_STATUS, PM_STATUS_READY);

postmaster进程接收信号：
sigusr1_handler->
 if (CheckPostmasterSignal(PMSIGNAL_RECOVERY_STARTED) &&
  pmState == PM_STARTUP && Shutdown == NoShutdown){
  CheckpointerPID = StartCheckpointer();
  BgWriterPID = StartBackgroundWriter();
  if (XLogArchivingAlways())
   PgArchPID = pgarch_start();
  //hot_standby在postgresql.conf文件中配置TRUE
  //表示在恢复的时候允许连接
  if (!EnableHotStandby){
   //将standby写入postmaster.pid文件，表示up但不允许连接
   AddToDataDirLockFile(LOCK_FILE_LINE_PM_STATUS, PM_STATUS_STANDBY);
  }
  pmState = PM_RECOVERY;
 }
 if (CheckPostmasterSignal(PMSIGNAL_BEGIN_HOT_STANDBY) &&
  pmState == PM_RECOVERY && Shutdown == NoShutdown){
  PgStatPID = pgstat_start();
  //将ready写入postmaster.pid文件，允许连接
  AddToDataDirLockFile(LOCK_FILE_LINE_PM_STATUS, PM_STATUS_READY);
  pmState = PM_HOT_STANDBY;
 }
 ...

StartupXLOG->
 ReadCheckpointRecord
 if (ArchiveRecoveryRequested && IsUnderPostmaster){//有recovery.conf文件则ArchiveRecoveryRequested为TRUE
  //有recovery.conf文件则ArchiveRecoveryRequested为TRUE
  PublishStartupProcessInformation();
  SetForwardFsyncRequests();
  //向master进程发送PMSIGNAL_RECOVERY_STARTED信号
  SendPostmasterSignal(PMSIGNAL_RECOVERY_STARTED);
  bgwriterLaunched = true;
 }
 CheckRecoveryConsistency();-->...
 |-- if (standbyState == STANDBY_SNAPSHOT_READY && !LocalHotStandbyActive &&
 |  reachedConsistency && IsUnderPostmaster){
 |  SpinLockAcquire(&XLogCtl->info_lck);
 |  XLogCtl->SharedHotStandbyActive = true;
 |  SpinLockRelease(&XLogCtl->info_lck);
 |  LocalHotStandbyActive = true;
 |  SendPostmasterSignal(PMSIGNAL_BEGIN_HOT_STANDBY);
 |-- }
 ...
 回放一个record后，每次读取下一个record前都会调用CheckRecoveryConsistency