一、問題
pg_ctl start啟動時報錯退出：pg_ctl：server did not start in time。超時時間是多少？從什么時候到哪個階段算超時？
二、分析：該信息打印位置，從后面代碼段do_start函數(shù)中可以看出
1、pg_ctl start調用start_postmaster啟動PG的主進程后，每隔0.1ms檢查一次postmaster.pid文件，是否已寫入ready/standby
2、總共會檢查600次，即從啟動主進程后，最多等待60s，如果沒有寫入ready/standby則打印上述日志并退出
3、默認等待時間是60s，如果pg_ctl start -t指定等待時間，則等待時間為該指定時間
三、什么時候postmaster.pid文件寫入ready/standby
1、如果是主機不管有沒有設置hot standby
1）當startup進程恢復完成退出時，調用proc_exit函數(shù)向主進程發(fā)送SIGCHLD信號并退出
2）主進程接收到信號后，signal處理函數(shù)reaper調用AddToDataDirLockFile向postmaster.pid文件寫入ready
2、如果是備機即data目錄下有recovery.cnf文件，且設置了hot standby，在實際恢復前沒有到達一致性位置
1）startup進程向主進程發(fā)送PMSIGNAL_RECOVERY_STARTED信號，主進程調用信號處理函數(shù)sigusr1_handler，將pmState=PM_RECOVERY
2）每次讀取下一個xlog前都會調用CheckRecoveryConsistency函數(shù)進行一致性檢查：
2.1 進入一致性狀態(tài)，starup進程向主進程發(fā)送PMSIGNAL_BEGIN_HOT_STANDBY信號，主進程接收到信號后調用sigusr1_handler->AddToDataDirLockFile向postmaster.pid文件寫入ready
3、如果是備機即data目錄下有recovery.cnf文件，且設置了hot standby，在實際恢復前沒有到達一致性位置
1）startup進程向主進程發(fā)送PMSIGNAL_RECOVERY_STARTED信號，主進程調用信號處理函數(shù)sigusr1_handler，將pmState=PM_RECOVERY
2）每次讀取下一個xlog前都會調用CheckRecoveryConsistency函數(shù)進行一致性檢查。如果沒有進入一致性狀態(tài)
3）本地日志恢復完成，切換日志源時同樣調用CheckRecoveryConsistency函數(shù)進行一致性檢查
3.1 進入一致性狀態(tài)，starup進程向主進程發(fā)送PMSIGNAL_BEGIN_HOT_STANDBY信號，主進程接收到信號后調用sigusr1_handler->AddToDataDirLockFile向postmaster.pid文件寫入ready
4、如果是備機即data目錄下有recovery.cnf文件，且設置了hot standby，在實際恢復前到達一致性位置
1）startup進程向主進程發(fā)送PMSIGNAL_RECOVERY_STARTED信號，主進程調用信號處理函數(shù)sigusr1_handler，將pmState=PM_RECOVERY
2）CheckRecoveryConsistency函數(shù)進行一致性檢查，向主進程發(fā)送PMSIGNAL_BEGIN_HOT_STANDBY信號，主進程接收到信號后調用sigusr1_handler->AddToDataDirLockFile向postmaster.pid文件寫入ready
5、如果是備機即data目錄下有recovery.cnf文件，沒有設置hot standby
1）startup進程向主進程發(fā)送PMSIGNAL_RECOVERY_STARTED信號
2）主進程接收到信號后，向postmaster.將pmState=PM_RECOVERY
四、代碼分析
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主進程及信號處理函數(shù)
PostmasterMain-> pqsignal_no_restart(SIGUSR1, sigusr1_handler); /* message from child process */ pqsignal_no_restart(SIGCHLD, reaper); /* handle child termination */ ... StartupXLOG(); ... proc_exit(0);//exit函數(shù)向主進程發(fā)送SIGCHLD信號
reaper->//進程終止或者停止的信號 AddToDataDirLockFile(LOCK_FILE_LINE_PM_STATUS, PM_STATUS_READY);
postmaster進程接收信號：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 //表示在恢復的時候允許連接 if (!EnableHotStandby){ //將standby寫入postmaster.pid文件，表示up但不允許連接 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(); //將ready寫入postmaster.pid文件，允許連接 AddToDataDirLockFile(LOCK_FILE_LINE_PM_STATUS, PM_STATUS_READY); pmState = PM_HOT_STANDBY; } ...3、Startup進程
StartupXLOG-> ReadCheckpointRecord if (ArchiveRecoveryRequested && IsUnderPostmaster){//有recovery.conf文件則ArchiveRecoveryRequested為TRUE //有recovery.conf文件則ArchiveRecoveryRequested為TRUE PublishStartupProcessInformation(); SetForwardFsyncRequests(); //向master進程發(fā)送PMSIGNAL_RECOVERY_STARTED信號 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); |-- } ... 回放一個record后，每次讀取下一個record前都會調用CheckRecoveryConsistency總結
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