PostgreSQL pg_ctl start超时分析
PostgreSQL pg_ctl start超时分析
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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