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7.4

SELECT ...FOR UPDATE locks entire table instead of one row

Asked by drew22 in MySQL Server

Tags: update, select, table, locks, entire

This SQL locks the table while processing. I'm trying to lock the only row that is returned by
SELECT access_code FROM access_codes WHERE retrieved = 0 LIMIT 1 FOR UPDATE

If I make the first request trigger the sleep function for 15 seconds, any subsequent requests backup until the first request is finished

Get your answer NOW

         
           
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             $db->sql('SET AUTOCOMMIT=0');
$db->sql('BEGIN');
	
list($access_code) = $db->getOne('SELECT access_code FROM access_codes WHERE retrieved = 0 LIMIT 1 FOR UPDATE');
	
if(! $access_code)
{
   $db->sql('ROLLBACK');
   message_exit('ERROR - out of access codes');
}	
	
// for testing...
if (isset($_GET['sleep']))
{
   $sec = (int) $_GET['sleep'];
   sleep($sec);
}	
		
	
$db->sql('UPDATE access_codes SET retrieved=retrieved+1 WHERE access_code = ' . mysql_safequote($access_code));
 
$db->sql('COMMIT');

           
         

SELECT ...FOR UPDATE locks entire table instead of one row

Asked by drew22 in MySQL Server

Tags: update, select, table, locks, entire

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