Index: includes/session.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/session.inc,v
retrieving revision 1.37.2.2
diff -u -6 -p -r1.37.2.2 session.inc
--- includes/session.inc	26 Jul 2007 19:16:45 -0000	1.37.2.2
+++ includes/session.inc	19 Feb 2008 23:19:23 -0000
@@ -60,23 +60,27 @@ function sess_write($key, $value) {
   // and one isn't being created ($value), do nothing.
   if (!session_save_session() || (empty($_COOKIE[session_name()]) && empty($value))) {
     return TRUE;
   }
 
   $result = db_query("SELECT sid FROM {sessions} WHERE sid = '%s'", $key);
+  $new_session = !db_num_rows($result);
 
-  if (!db_num_rows($result)) {
+  if ($new_session) {
     // Only save session data when when the browser sends a cookie. This keeps
     // crawlers out of session table. This reduces memory and server load,
     // and gives more useful statistics. We can't eliminate anonymous session
     // table rows without breaking throttle module and "Who's Online" block.
     if ($user->uid || $value || count($_COOKIE)) {
-      db_query("INSERT INTO {sessions} (sid, uid, cache, hostname, session, timestamp) VALUES ('%s', %d, %d, '%s', '%s', %d)", $key, $user->uid, $user->cache, $_SERVER["REMOTE_ADDR"], $value, time());
+      // If the insert fails, it is usually because another parallel server 
+      // thread got here first.
+      $new_session = @db_query("INSERT INTO {sessions} (sid, uid, cache, hostname, session, timestamp) VALUES ('%s', %d, %d, '%s', '%s', %d)", $key, $user->uid, $user->cache, $_SERVER["REMOTE_ADDR"], $value, time());
     }
   }
-  else {
+
+  if (!$new_session) {
     db_query("UPDATE {sessions} SET uid = %d, cache = %d, hostname = '%s', session = '%s', timestamp = %d WHERE sid = '%s'", $user->uid, $user->cache, $_SERVER["REMOTE_ADDR"], $value, time(), $key);
 
     // TODO: this can be an expensive query. Perhaps only execute it every x minutes. Requires investigation into cache expiration.
     if ($user->uid) {
       db_query("UPDATE {users} SET access = %d WHERE uid = %d", time(), $user->uid);
     }