PostgreSQL pg_ctl start启动超时实例分析

数据库  /  管理员 发布于 5年前   1415

一、问题

pg_ctl start启动时报错退出：pg_ctl：server did not start in time。超时时间是多少？从什么时候到哪个阶段算超时？

二、分析：该信息打印位置，从后面代码段do_start函数中可以看出

1、pg_ctl start调用start_postmaster启动PG的主进程后，每隔0.1ms检查一次postmaster.pid文件，是否已写入ready/standby

2、总共会检查600次，即从启动主进程后，最多等待60s，如果没有写入ready/standby则打印上述日志并退出

3、默认等待时间是60s，如果pg_ctl start -t指定等待时间，则等待时间为该指定时间

三、什么时候postmaster.pid文件写入ready/standby

1、如果是主机不管有没有设置hot standby

1）当startup进程恢复完成退出时，调用proc_exit函数向主进程发送SIGCHLD信号并退出

2）主进程接收到信号后，signal处理函数reaper调用AddToDataDirLockFile向postmaster.pid文件写入ready

2、如果是备机即data目录下有recovery.cnf文件，且设置了hot standby，在实际恢复前没有到达一致性位置

1）startup进程向主进程发送PMSIGNAL_RECOVERY_STARTED信号，主进程调用信号处理函数sigusr1_handler，将pmState=PM_RECOVERY

2）每次读取下一个xlog前都会调用CheckRecoveryConsistency函数进行一致性检查：

2.1 进入一致性状态，starup进程向主进程发送PMSIGNAL_BEGIN_HOT_STANDBY信号，主进程接收到信号后调用sigusr1_handler->AddToDataDirLockFile向postmaster.pid文件写入ready

3、如果是备机即data目录下有recovery.cnf文件，且设置了hot standby，在实际恢复前没有到达一致性位置

1）startup进程向主进程发送PMSIGNAL_RECOVERY_STARTED信号，主进程调用信号处理函数sigusr1_handler，将pmState=PM_RECOVERY

2）每次读取下一个xlog前都会调用CheckRecoveryConsistency函数进行一致性检查。如果没有进入一致性状态

3）本地日志恢复完成，切换日志源时同样调用CheckRecoveryConsistency函数进行一致性检查

3.1 进入一致性状态，starup进程向主进程发送PMSIGNAL_BEGIN_HOT_STANDBY信号，主进程接收到信号后调用sigusr1_handler->AddToDataDirLockFile向postmaster.pid文件写入ready

4、如果是备机即data目录下有recovery.cnf文件，且设置了hot standby，在实际恢复前到达一致性位置

1）startup进程向主进程发送PMSIGNAL_RECOVERY_STARTED信号，主进程调用信号处理函数sigusr1_handler，将pmState=PM_RECOVERY

2）CheckRecoveryConsistency函数进行一致性检查，向主进程发送PMSIGNAL_BEGIN_HOT_STANDBY信号，主进程接收到信号后调用sigusr1_handler->AddToDataDirLockFile向postmaster.pid文件写入ready

5、如果是备机即data目录下有recovery.cnf文件，没有设置hot standby

1）startup进程向主进程发送PMSIGNAL_RECOVERY_STARTED信号

2）主进程接收到信号后，向postmaster.将pmState=PM_RECOVERY

四、代码分析

1、pg_ctl start流程

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;

2、server主进程及信号处理函数

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; } ...

3、Startup进程

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

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