typedef enum DBState { DB_STARTUP = 0, DB_SHUTDOWNED, DB_SHUTDOWNED_IN_RECOVERY, DB_SHUTDOWNING, DB_IN_CRASH_RECOVERY, DB_IN_ARCHIVE_RECOVERY, DB_IN_PRODUCTION } DBState;
PostgreSQL啓動以及關閉或運行過程中的狀態包括以上七種。在pg_controldata獲取的內容Database cluster state一欄顯示的是DB的狀態。其中:
DB_STARTUP:表示數據庫正在啓動狀態,實際上沒有使用該狀態。
DB_SHUTDOWNED:數據庫實例正常關閉(非standby)控制文件寫入的狀態就是這個狀態
DB_SHUTDOWNED_IN_RECOVERY:standby實例正常關閉,控制文件寫入的狀態是這個狀態。是由CreateRestartPoint修改該狀態。
DB_SHUTDOWNING:非standby實例在關閉時,做checkpoint:CreateCheckPoint,開始做時修改爲該狀態,做完後修改爲DB_SHUTDOWNED狀態。
DB_IN_CRASH_RECOVERY:實例異常關閉,重啓後,恢復時需要將實例先置爲該狀態
DB_IN_ARCHIVE_RECOVERY:standby實例重啓後置爲該狀態。
DB_IN_PRODUCTION:非standby實例正常重啓後就是這個狀態,standby是DB_IN_ARCHIVE_RECOVERY
分析
1、DB_STARTUP
initdb->BootStrapXLOG: memset(ControlFile, 0, sizeof(ControlFileData)); ... ControlFile->state = DB_SHUTDOWNED; ... WriteControlFile();
初始化時,首先將其狀態初始化爲DB_STARTUP,然後立即置成DB_SHUTDOWNED並將其刷寫到磁盤。
2、StartupXLOG
StartupXLOG-> ReadControlFile(); ... readRecoveryCommandFile();-> |--... | for (item = head; item; item = item->next){ | if (strcmp(item->name, "restore_command") == 0){ | ... | }... | else if (strcmp(item->name, "standby_mode") == 0){ | if (!parse_bool(item->value, &StandbyModeRequested)) | }... | } | ... |-- ArchiveRecoveryRequested = true; ... if (ArchiveRecoveryRequested && (ControlFile->minRecoveryPoint != InvalidXLogRecPtr || ControlFile->backupEndRequired || ControlFile->backupEndPoint != InvalidXLogRecPtr || ControlFile->state == DB_SHUTDOWNED)){ InArchiveRecovery = true; if (StandbyModeRequested) StandbyMode = true; } ... record = ReadCheckpointRecord(xlogreader, checkPointLoc, 1, true); ... if (InRecovery){ if (InArchiveRecovery)//何時? ControlFile->state = DB_IN_ARCHIVE_RECOVERY; else ControlFile->state = DB_IN_CRASH_RECOVERY; ... UpdateControlFile(); replay... } ... LWLockAcquire(ControlFileLock, LW_EXCLUSIVE); ControlFile->state = DB_IN_PRODUCTION; UpdateControlFile(); LWLockRelease(ControlFileLock); ...
只要有recovery.conf文件,ArchiveRecoveryRequested即爲TRUE->InArchiveRecovery = true,配置了standby_mode=on,那麼StandbyMode=TRUE。這樣standby啓動後,ControlFile->state爲DB_IN_ARCHIVE_RECOVERY狀態。
3、checkpoint
CheckpointerMain-> for (;;){ ... if (shutdown_requested){ ShutdownXLOG(0, 0);-> |--if (RecoveryInProgress()){ | CreateRestartPoint(CHECKPOINT_IS_SHUTDOWN | CHECKPOINT_IMMEDIATE); | }else{ | CreateCheckPoint(CHECKPOINT_IS_SHUTDOWN | CHECKPOINT_IMMEDIATE); | } |--... proc_exit(0); } ... if (do_checkpoint){ do_restartpoint = RecoveryInProgress(); ... if (flags & CHECKPOINT_END_OF_RECOVERY)//flags從哪來? do_restartpoint = false; ... if (!do_restartpoint){ CreateCheckPoint(flags); ckpt_performed = true; } else ckpt_performed = CreateRestartPoint(flags); } }
備機上做checkpoint調用CreateRestartPoint,主機做checkpoint調用CreateCheckPoint
CreateCheckPoint(int flags)-> if (flags & (CHECKPOINT_IS_SHUTDOWN | CHECKPOINT_END_OF_RECOVERY)) shutdown = true; else shutdown = false; ... if (shutdown){ LWLockAcquire(ControlFileLock, LW_EXCLUSIVE); ControlFile->state = DB_SHUTDOWNING; ControlFile->time = (pg_time_t) time(NULL); UpdateControlFile(); LWLockRelease(ControlFileLock); } ... LWLockAcquire(ControlFileLock, LW_EXCLUSIVE); if (shutdown) ControlFile->state = DB_SHUTDOWNED; ... UpdateControlFile(); LWLockRelease(ControlFileLock);
shutdown時,先將狀態置爲DB_SHUTDOWNING,最後將狀態置爲DB_SHUTDOWNED
CreateRestartPoint(int flags)-> LWLockAcquire(CheckpointLock, LW_EXCLUSIVE); SpinLockAcquire(&XLogCtl->info_lck); lastCheckPointRecPtr = XLogCtl->lastCheckPointRecPtr; lastCheckPointEndPtr = XLogCtl->lastCheckPointEndPtr; lastCheckPoint = XLogCtl->lastCheckPoint; SpinLockRelease(&XLogCtl->info_lck); if (!RecoveryInProgress()){ LWLockRelease(CheckpointLock); return false; } ... if (XLogRecPtrIsInvalid(lastCheckPointRecPtr) ||lastCheckPoint.redo <= ControlFile->checkPointCopy.redo){ UpdateMinRecoveryPoint(InvalidXLogRecPtr, true); if (flags & CHECKPOINT_IS_SHUTDOWN){ LWLockAcquire(ControlFileLock, LW_EXCLUSIVE); ControlFile->state = DB_SHUTDOWNED_IN_RECOVERY; ControlFile->time = (pg_time_t) time(NULL); UpdateControlFile(); LWLockRelease(ControlFileLock); } LWLockRelease(CheckpointLock); return false; } ... LWLockAcquire(ControlFileLock, LW_EXCLUSIVE); if (ControlFile->state == DB_IN_ARCHIVE_RECOVERY && ControlFile->checkPointCopy.redo < lastCheckPoint.redo){ ... if (flags & CHECKPOINT_IS_SHUTDOWN) ControlFile->state = DB_SHUTDOWNED_IN_RECOVERY; UpdateControlFile(); } LWLockRelease(ControlFileLock); ...
備機shutdown,將狀態置爲DB_SHUTDOWNED_IN_RECOVERY