Hi

can a php page be used by 2 people at the same time or will one page load be completed before another person can call it?

I have a registration form which, when processed will update several tables at once. Nothing new there, but ive come accross something which i feel could ultimately be a problem and that is a very common procedure. it goes like this -

my user table has a userid field which is auto increment, and my images table has a userid id field which is not auto increment. During a transaction i add a row to my user table, which auto increments the userid column, then before i confirm the transaction i need to enter the user's image information and tie it to the user table with the userid which has just been assigned to the user table.

my transaction would look something like this -

BEGIN TRANSACTION

ENTER USER TABLE INFO

SELECT RECENT USERID FROM USER TABLE

(increment userid as the entry above hasnt been confirmed yet)
$userid=($userid+1)

ENTER IMAGES TABLE INFO WITH $userid as key

CONFIRM OR DECLINE TRANSACTION

What would happen if 2 people submitted their registration forms within nano seconds of one another and the SELECT USERID query of user 2 retrieved the userid of user 1 whos transaction had been confirmed between the ENTER USER TABLE query and the SELECT USERID query of user 2?

I hope this makes some sense. Its a very simple concept that i have difficulty explaining.

thanks in advance

mark

It's all handled by the server, as long as your have a normal server and aren't trying to do it with 64K RAM or something you shouldn't face an issue because it'll handle it fast enough. From what I see you have something like:

PHP Code:

$query = "insert into user_table values(NULL)";
$result = mysql_query($query);
$idget = "select user_id from user_table sort by user_id DESC limit 1";
$getid = mysql_query($idget);
$userid = mysql_fetch_array($getid);
$userid = $userid[0];
$picput = "insert into pic_table values('$userid',$img)";
$putpic = mysql_query($picput); 


That would all be run as the page was parsed, let's call the users user_1 and user_2. When user_1 requests that to be parsed it starts parse_job_1 user_2 then asks for it to be parsed and it queues parse_job_2 until parse_job_1 finishes. Then it'll run parse_job_2. Now then if you're reloading the page etc then you could have an issue there.

Don't use a separate query for retreiving the user id, use mysql_insert_id function.

i know its very unlikely to happen arenlor, but it only needs to happen once to wreak a fair bit of havoc which is quite difficult to rectify afterwards.

the mysql_insert_id function is exactly what i was looking for thanks dman.