初步学习pg_control文件之三

/*                                            
 * 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);                                        
                                            
    …                                        
                                            
}