接前文 初步学习pg_control文件之四，继续看何时出现 DB_IN_CRASH_RECOVERY：
看下面代码就比较清楚了：如果对 InArchiveRecovery 判断值为假，而且 读取出来pg_control文件的 state不是 SHUTDOWNED状态，表明当初没有来得及把SHUTDOWNED状态写入到pg_control文件，那么就是说系统已经崩溃了。
/*
* This must be called ONCE during postmaster or standalone-backend startup
*/
void
StartupXLOG(void)
{ …
/*
* Read control file and check XLOG status looks valid.
*
* Note: in most control paths, *ControlFile is already valid and we need
* not do ReadControlFile() here, but might as well do it to be sure.
*/
ReadControlFile(); …
/*
* Check whether we need to force recovery from WAL. If it appears to
* have been a clean shutdown and we did not have a recovery.conf file,
* then assume no recovery needed.
*/
if (XLByteLT(checkPoint.redo, RecPtr))
{
if (wasShutdown)
ereport(PANIC,
(errmsg("invalid redo record in shutdown checkpoint")));
InRecovery = true;
}
else if (ControlFile->state != DB_SHUTDOWNED)
InRecovery = true;
else if (InArchiveRecovery)
{
/* force recovery due to presence of recovery.conf */
InRecovery = true;
} /* REDO */
if (InRecovery)
{
…
/*
* Update pg_control to show that we are recovering and to show the
* selected checkpoint as the place we are starting from. We also mark
* pg_control with any minimum recovery stop point obtained from a
* backup history file.
*/
if (InArchiveRecovery)
ControlFile->state = DB_IN_ARCHIVE_RECOVERY;
else
{
ereport(LOG,
(errmsg("database system was not properly shut down; "
automatic recovery in progress)));
ControlFile->state = DB_IN_CRASH_RECOVERY;
}
…
}
…
}
然而，还需要把整个拼图补上一块，在正常关闭的时候，是如何把SHUTDOWNED状态写入到pg_control文件中的。
注意下面出现的updateControlFile：
/*
* 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;
ControlFile->checkPoint = ProcLastRecPtr;
ControlFile->checkPointCopy = checkPoint;
ControlFile->time = (pg_time_t) time(NULL);
/* crash recovery should always recover to the end of WAL */
MemSet(&ControlFile->minRecoveryPoint, , sizeof(XLogRecPtr));
UpdateControlFile();
LWLockRelease(ControlFileLock);
…
}