PostgreSQL pg_ctl start啟動超時例項分析
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?從什麼時候到哪個階段算超時?
二、分析:該資訊列印位置,從後面程式碼段do_start函式中可以看出
1、pg_ctl start呼叫start_postmaster啟動PG的主程序後,每隔0.1ms檢查一次postmaster.pid檔案,是否已寫入ready/standby
2、總共會檢查600次,即從啟動主程序後,最多等待60s,如果沒有寫入ready/standby則列印上述日誌並退出
3、預設等待時間是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、什麼時候postmaster.pid檔案寫入ready/standby
1、如果是主機不管有沒有設定hot standby
1)當startup程序恢復完成退出時,呼叫proc_exit函式向主程序傳送SIGCHLD訊號並退出
2)主程序接收到訊號後,signal處理函式reaper呼叫AddToDataDirLockFile向postmaster.pid檔案寫入ready
2、如果是備機即data目錄下有recovery.cnf檔案,且設定了hot standby,在實際恢復前沒有到達一致性位置
1)startup程序向主程序傳送PMSIGNAL_RECOVERY_STARTED訊號,主程序呼叫訊號處理函式sigusr1_handler,將pmState=PM_RECOVERY
2)每次讀取下一個xlog前都會呼叫CheckRecoveryConsistency函式進行一致性檢查:
2.1 進入一致性狀態,starup程序向主程序傳送PMSIGNAL_BEGIN_HOT_STANDBY訊號,主程序接收到訊號後呼叫sigusr1_handler->AddToDataDirLockFile向postmaster.pid檔案寫入ready
3、如果是備機即data目錄下有recovery.cnf檔案,且設定了hot standby,在實際恢復前沒有到達一致性位置
1)startup程序向主程序傳送PMSIGNAL_RECOVERY_STARTED訊號,主程序呼叫訊號處理函式sigusr1_handler,將pmState=PM_RECOVERY
2)每次讀取下一個xlog前都會呼叫CheckRecoveryConsistency函式進行一致性檢查。如果沒有進入一致性狀態
3)本地日誌恢復完成,切換日誌源時同樣呼叫CheckRecoveryConsistency函式進行一致性檢查
3.1 進入一致性狀態,starup程序向主程序傳送PMSIGNAL_BEGIN_HOT_STANDBY訊號,主程序接收到訊號後呼叫sigusr1_handler->AddToDataDirLockFile向postmaster.pid檔案寫入ready
4、如果是備機即data目錄下有recovery.cnf檔案,且設定了hot standby,在實際恢復前到達一致性位置
1)startup程序向主程序傳送PMSIGNAL_RECOVERY_STARTED訊號,主程序呼叫訊號處理函式sigusr1_handler,將pmState=PM_RECOVERY
2)CheckRecoveryConsistency函式進行一致性檢查,向主程序傳送PMSIGNAL_BEGIN_HOT_STANDBY訊號,主程序接收到訊號後呼叫sigusr1_handler->AddToDataDirLockFile向postmaster.pid檔案寫入ready
5、如果是備機即data目錄下有recovery.cnf檔案,沒有設定hot standby
1)startup程序向主程序傳送PMSIGNAL_RECOVERY_STARTED訊號
2)主程序接收到訊號後,向postmaster.將pmState=PM_RECOVERY
四、程式碼分析
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主程序及訊號處理函式
PostmasterMain-> pqsignal_no_restart(SIGUSR1,sigusr1_handler); /* message from child process */ pqsignal_no_restart(SIGCHLD,reaper); /* handle child termination */ ... StartupXLOG(); ... proc_exit(0);//exit函式向主程序傳送SIGCHLD訊號
reaper->//程序終止或者停止的訊號 AddToDataDirLockFile(LOCK_FILE_LINE_PM_STATUS,PM_STATUS_READY);
postmaster程序接收訊號: 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檔案中配置TRUE //表示在恢復的時候允許連線 if (!EnableHotStandby){ //將standby寫入postmaster.pid檔案,表示up但不允許連線 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檔案,允許連線 AddToDataDirLockFile(LOCK_FILE_LINE_PM_STATUS,PM_STATUS_READY); pmState = PM_HOT_STANDBY; } ...
3、Startup程序
StartupXLOG-> ReadCheckpointRecord if (ArchiveRecoveryRequested && IsUnderPostmaster){//有recovery.conf檔案則ArchiveRecoveryRequested為TRUE //有recovery.conf檔案則ArchiveRecoveryRequested為TRUE PublishStartupProcessInformation(); SetForwardFsyncRequests(); //向master程序傳送PMSIGNAL_RECOVERY_STARTED訊號 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後,每次讀取下一個record前都會呼叫CheckRecoveryConsistency
總結
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