接前文，初步学习pg_control文件之三 继续分析
何时出现 DB_SHUTDOWNING状态：
在正常的shutdown的时候，需要进行checkpoint，所以就在此处，设置pg_control文件的state状态为DB_SHUTDOWNING。
/* * Perform a checkpoint --- either during shutdown, or on-the-fly * * flags is a bitwise OR of the following: * CHECKPOINT_IS_SHUTDOWN: checkpoint is for database shutdown. * CHECKPOINT_END_OF_RECOVERY: checkpoint is for end of WAL recovery. * CHECKPOINT_IMMEDIATE: finish the checkpoint ASAP, * ignoring checkpoint_completion_target parameter. * CHECKPOINT_FORCE: force a checkpoint even if no XLOG activity has occured * since the last one (implied by CHECKPOINT_IS_SHUTDOWN or * CHECKPOINT_END_OF_RECOVERY). * * Note: flags contains other bits, of interest here only for logging purposes. * In particular note that this routine is synchronous and does not pay * attention to CHECKPOINT_WAIT. */ void CreateCheckPoint(int flags) { ... if (shutdown) { LWLockAcquire(ControlFileLock, LW_EXCLUSIVE); ControlFile->state = DB_SHUTDOWNING; ControlFile->time = (pg_time_t) time(NULL); UpdateControlFile(); LWLockRelease(ControlFileLock); } ... }
更进一步地说，是这样的：先是Shutdowning， 后来就变化为Shutdowned
/* * Perform a checkpoint --- either during shutdown, or on-the-fly * * flags is a bitwise OR of the following: * CHECKPOINT_IS_SHUTDOWN: checkpoint is for database shutdown. * CHECKPOINT_END_OF_RECOVERY: checkpoint is for end of WAL recovery. * CHECKPOINT_IMMEDIATE: finish the checkpoint ASAP, * ignoring checkpoint_completion_target parameter. * CHECKPOINT_FORCE: force a checkpoint even if no XLOG activity has occured * since the last one (implied by CHECKPOINT_IS_SHUTDOWN or * CHECKPOINT_END_OF_RECOVERY). * * Note: flags contains other bits, of interest here only for logging purposes. * In particular note that this routine is synchronous and does not pay * attention to CHECKPOINT_WAIT. */ void CreateCheckPoint(int flags) { … if (shutdown) { LWLockAcquire(ControlFileLock, LW_EXCLUSIVE); ControlFile->state = DB_SHUTDOWNING; ControlFile->time = (pg_time_t) time(NULL); UpdateControlFile(); LWLockRelease(ControlFileLock); } … /* * Update the control file. */ LWLockAcquire(ControlFileLock, LW_EXCLUSIVE); if (shutdown) ControlFile->state = DB_SHUTDOWNED; ControlFile->prevCheckPoint = ControlFile->checkPoint; … }
