初步学习pg_control文件之五

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);
    …
}