Can MySQL support concurrent queries per connection? - mysql

Question

If I have 10 queries, and each query is updating a particular table (i.e., 10 different tables).
Can I open one mySQL connection, spawn 10 threads, each thread handles 1 query such that they can run concurrently instead of executing one by one.
Thanks!

Answer 1

No you can't:
MySQL client library (at least native C one) is not thread safe to use same connection from different threads. You need to use a connection per thread.

Answer 2

If you just need update/insert queries running in parallel (asynchronously in terms of MySQL API) - you can use INSERT DELAYED and UPDATE LOW_PRIORITY queries.

Answer 3

Because of the way the MySQL protocol works, these will get sent to the server one-by-one if you only have one connection open.

Answer 4

There is no file "log.conn.txt" created, so there is no conflict between concurrent queries to the single mysql client connection:
<?
declare(ticks=1);
pcntl_signal(SIGUSR1, create_function('$signo', 'sleep(1);while (($pid=pcntl_wait(#$status, WNOHANG))>0) {}'));//protect against zombie children
$pdo=new PDO('mysql:host=192.168.0.2;port=3306;dbname=baseinfo', 'dev', 'dev',
array(PDO::ATTR_ERRMODE=>PDO::ERRMODE_EXCEPTION,
PDO::MYSQL_ATTR_INIT_COMMAND=>'set names utf8'
)
);
for ($i=0; $i<20; ++$i)
{if (($pid=pcntl_fork())===-1)
{//...
continue;
}
else if ($pid)
{$pids[]=$pid;
pcntl_wait($status, WNOHANG); //protect against zombie children, one wait vs one child
}
else if ($pid===0)
{ob_start();//prevent output to main process
register_shutdown_function(create_function('$pars', 'ob_end_clean();posix_kill(posix_getppid(), SIGUSR1);posix_kill(getmypid(), SIGKILL);'), array());//to kill self before exit();, or else the resource shared with parent will be closed
for ($j=0; $j<200; ++$j)
{try
{file_put_contents('log.'.$i.'.txt', $pdo->query('select partner_login from base_account where id=100')->fetch(PDO::FETCH_COLUMN, 0)."\t".time().substr(microtime(),2,6)."\n", FILE_APPEND);
}
catch (Exception $e)
{if ($pdo->getAttribute(PDO::ATTR_SERVER_INFO)==='MySQL server has gone away')
{file_put_contents('log.conn.txt', time().substr(microtime(),2,6).":{$i}:{$j} lost\n", FILE_APPEND);
$pdo=&new PDO('mysql:host=192.168.0.2;port=3306;dbname=baseinfo', 'dev', 'dev',
array(PDO::ATTR_ERRMODE=>PDO::ERRMODE_EXCEPTION,
PDO::MYSQL_ATTR_INIT_COMMAND=>'set names utf8'
)
);
}
}
usleep(50000);
}
exit();//avoid foreach loop in child process
}
}
//wait all child to end, avoid close db connection before all children self killed
foreach ($pids as $p)
{pcntl_waitpid($p, $status);
}
?>