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04.28.2008 at 02:21PM PDT, ID: 23360293
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7.4

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

Asked by drew22 in MySQL Server

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 finishedStart Free Trial 
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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');
[+][-]04.28.2008 at 02:55PM PDT, ID: 21457992

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[+][-]04.28.2008 at 02:57PM PDT, ID: 21457999

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[+][-]04.28.2008 at 03:28PM PDT, ID: 21458189

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[+][-]04.28.2008 at 03:31PM PDT, ID: 21458216

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[+][-]04.28.2008 at 03:45PM PDT, ID: 21458299

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[+][-]04.28.2008 at 04:00PM PDT, ID: 21458372

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[+][-]04.28.2008 at 04:33PM PDT, ID: 21458527

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[+][-]04.28.2008 at 04:35PM PDT, ID: 21458539

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[+][-]04.28.2008 at 04:39PM PDT, ID: 21458552

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[+][-]04.28.2008 at 04:42PM PDT, ID: 21458566

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About this solution

Zone: MySQL Server
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Solution Provided By: paulop1975
Participating Experts: 1
Solution Grade: A
 
 
 
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