=== modified file 'modules/system/system.install'
--- modules/system/system.install	2009-10-05 04:34:04 +0000
+++ modules/system/system.install	2009-10-12 14:43:39 +0000
@@ -1226,12 +1226,6 @@ function system_schema() {
         'default' => '',
         'description' => 'The queue name.',
       ),
-      'consumer_id' => array(
-        'type' => 'int',
-        'not null' => TRUE,
-        'default' => 0,
-        'description' => 'The ID of the dequeuing consumer.',
-      ),
       'data' => array(
         'type' => 'text',
         'not null' => FALSE,
@@ -1254,23 +1248,11 @@ function system_schema() {
     ),
     'primary key' => array('item_id'),
     'indexes' => array(
-      'consumer_queue' => array('consumer_id', 'name', 'created'),
-      'consumer_expire' => array('consumer_id', 'expire'),
+      'name_created' => array('name', 'created'),
+      'expire' => array('expire'),
     ),
   );
 
-  $schema['queue_consumer_id'] = array(
-    'description' => 'Stores queue consumer IDs, used to auto-increment the consumer ID so that a unique consumer ID is used.',
-    'fields' => array(
-      'consumer_id'  => array(
-        'type' => 'serial',
-        'not null' => TRUE,
-        'description' => 'Primary Key: Unique consumer ID used to make sure only one consumer gets one item.',
-      ),
-    ),
-    'primary key' => array('consumer_id'),
-  );
-
   $schema['registry'] = array(
     'description' => "Each record is a function, class, or interface name and the file it is in.",
     'fields' => array(

=== modified file 'modules/system/system.queue.inc'
--- modules/system/system.queue.inc	2009-10-10 13:32:01 +0000
+++ modules/system/system.queue.inc	2009-10-12 14:44:40 +0000
@@ -182,7 +182,6 @@ class SystemQueue implements DrupalQueue
     $record = new stdClass();
     $record->name = $this->name;
     $record->data = $data;
-    $record->consumer_id = 0;
     // We cannot rely on REQUEST_TIME because many items might be created by a
     // single request which takes longer than 1 second.
     $record->created = time();
@@ -194,30 +193,25 @@ class SystemQueue implements DrupalQueue
   }
 
   public function claimItem($lease_time = 30) {
-    if (!isset($this->consumerId)) {
-      $this->consumerId = db_insert('queue_consumer_id')
-        ->useDefaults(array('consumer_id'))
-        ->execute();
-    }
-    // Claim an item by updating its consumer_id and expire fields. If claim
-    // is not successful another thread may have claimed the item in the
-    // meantime. Therefore loop until an item is successfully claimed or we are
-    // reasonably sure there are no unclaimed items left.
+    // Claim an item by updating its expire fields. If claim is not successful
+    // another thread may have claimed the item in the meantime. Therefore loop
+    // until an item is successfully claimed or we are reasonably sure there
+    // are no unclaimed items left.
     while (TRUE) {
-      $item = db_query_range('SELECT data, item_id FROM {queue} q WHERE consumer_id = 0 AND name = :name ORDER BY created ASC', 0, 1, array(':name' => $this->name))->fetchObject();
+      $item = db_query_range('SELECT data, item_id FROM {queue} q WHERE name = :name ORDER BY created ASC', 0, 1, array(':name' => $this->name))->fetchObject();
       if ($item) {
-        // Try to mark the item as ours. We cannot rely on REQUEST_TIME
-        // because items might be claimed by a single consumer which runs
-        // longer than 1 second. If we continue to use REQUEST_TIME instead of
-        // the current time(), we steal time from the lease, and will tend to
-        // reset items before the lease should really expire.
+        // Try to update the item. Only one thread can succeed in UPDATEing the
+        // same row. We cannot rely on REQUEST_TIME because items might be
+        // claimed by a single consumer which runs longer than 1 second. If we
+        // continue to use REQUEST_TIME instead of the current time(), we steal
+        // time from the lease, and will tend to reset items before the lease
+        // should really expire.
         $update = db_update('queue')
           ->fields(array(
-            'consumer_id' => $this->consumerId,
             'expire' => time() + $lease_time,
           ))
           ->condition('item_id', $item->item_id)
-          ->condition('consumer_id', 0);
+          ->condition('expire', 0);
         // If there are affected rows, this update succeeded.
         if ($update->execute()) {
           $item->data = unserialize($item->data);