[support] User ID in users table

[Jamie Holly]

UID is figured by select max(uid). Here is the exact code from user.module:

  if (empty($account->uid)) {
         $account->uid = db_next_id(db_query('SELECT MAX(uid) FROM 
{users}')->fetchField());
       }
       // Allow 'created' to be set by the caller.
       if (!isset($account->created)) {
         $account->created = REQUEST_TIME;
       }
       $success = drupal_write_record('users', $account);

$account->uid == 0, which is the same as empty.

Other modules can influence this via the API, such as hook_user_presave, 
but for the core functionality, this is how the UID is figured.


Jamie Holly
http://www.intoxination.net
http://www.hollyit.net

On 11/30/2012 9:44 PM, Michael Prasuhn wrote:
> No. If if was just using SELECT MAX(uid) FROM {users} then it wouldn't have gaps like the OP was experiencing.
>
> Note that the result from that query is actually fed to db_next_id() which in turn uses a DBMS specific method to ensure unique IDs. (In MySQL this means using an insert query into a table that is set to auto increment and then reading the ID of the inserted record. This cannot produce duplicate keys. see http://api.drupal.org/api/drupal/includes%21database%21mysql%21database.inc/function/DatabaseConnection_mysql%3A%3AnextId/7 )
>
> -Mike
> __________________
> Michael Prasuhn
> http://mikeyp.net
>
> On Nov 30, 2012, at 5:42 AM, Earnie Boyd <earnie at users.sourceforge.net> wrote:
>
> > On Fri, Nov 30, 2012 at 8:32 AM, Jamie Holly wrote:
> >> This isn't the case in D7.  UID is assigned by a SELECT MAX(uid) FROM
> >> {users}. Check user.module line 571.
> >
> > Unless the whole users table is locked then this is guaranteed to fail
> > under heavy use.  Some poor user is going to get a DB error of
> > duplicate key.  The chances may be small but there is a chance it will
> > happen.  Do you know the issue # that caused this to happen?
> >
> > --
> > Earnie
> > -- https://sites.google.com/site/earnieboyd
> > --
> > [ Drupal support list | http://lists.drupal.org/ ]
>