初步学习pg_control文件之三

接前文，初步学习pg_control文件之二

继续学习：

研究 DBState，先研究 DB_IN_PRODUCTION ，看它如何出现：

它出现在启动Postmaster时运行的函数处：

/*
 * 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();                                        

    if (ControlFile->state < DB_SHUTDOWNED ||
        ControlFile->state > DB_IN_PRODUCTION ||
        !XRecOffIsValid(ControlFile->checkPoint.xrecoff))
        ereport(FATAL,(errmsg("control file contains invalid data")));                            

    if (ControlFile->state == DB_SHUTDOWNED)
        ereport(LOG, errmsg("database system was shut down at %s", str_time(ControlFile->time))));
    else if (ControlFile->state == DB_SHUTDOWNED_IN_RECOVERY)
        ereport(LOG,(errmsg("database system was shut down in recovery at %s", 
                        str_time(ControlFile->time))));
 
    else if (ControlFile->state == DB_SHUTDOWNING)
        ereport(LOG,(errmsg("database system shutdown was interrupted; last known up at %s",
                        str_time(ControlFile->time))));                    

    else if (ControlFile->state == DB_IN_CRASH_RECOVERY)
        ereport(LOG,
           (errmsg("database system was interrupted while in recovery at %s",
                   str_time(ControlFile->time)),
            errhint("This probably means that some data is corrupted and"
                     you will have to use the last backup for recovery.)));                        

    else if (ControlFile->state == DB_IN_ARCHIVE_RECOVERY)
        ereport(LOG, (errmsg("database system was interrupted while in recovery at log time %s",
                str_time(ControlFile->checkPointCopy.time)),
                errhint("If this has occurred more than once some data might be corrupted
                    and you might need to choose an earlier recovery target.")));                          

    else if (ControlFile->state == DB_IN_PRODUCTION)
        ereport(LOG,(errmsg("database system was interrupted; last known up at %s",
                      str_time(ControlFile->time))));                        

    /* This is just to allow attaching to startup process with a debugger */
    #ifdef XLOG_REPLAY_DELAY
    if (ControlFile->state != DB_SHUTDOWNED)
        pg_usleep(60000000L);
    #endif                                        

    …
    /*
     * 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))
    {
        …
    }
    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;
        }                                    

        …
    }                                        

    …                                        

    /*
     * Okay, we're officially UP.
     */
    InRecovery = false;                                        

    LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
    ControlFile->state = DB_IN_PRODUCTION;
    ControlFile->time = (pg_time_t) time(NULL);
    UpdateControlFile();
    LWLockRelease(ControlFileLock);                                        

    …                                        

}                                            

可以说，只要是正常启动了，那么就是DB_IN_PRODUCTION状态。