Index: includes/bootstrap.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/bootstrap.inc,v
retrieving revision 1.165
diff -u -r1.165 bootstrap.inc
--- includes/bootstrap.inc	8 May 2007 16:36:55 -0000	1.165
+++ includes/bootstrap.inc	17 May 2007 06:23:47 -0000
@@ -444,10 +444,10 @@
 function variable_set($name, $value) {
   global $conf;
 
-  db_lock_table('variable');
-  db_query("DELETE FROM {variable} WHERE name = '%s'", $name);
-  db_query("INSERT INTO {variable} (name, value) VALUES ('%s', '%s')", $name, serialize($value));
-  db_unlock_tables();
+  db_query_replace(
+    array("DELETE FROM {variable} WHERE name = '%s'", $name),
+    array("INSERT INTO {variable} (name, value) VALUES ('%s', '%s')", $name, serialize($value))
+  );
 
   cache_clear_all('variables', 'cache');
 
Index: includes/cache.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/cache.inc,v
retrieving revision 1.11
diff -u -r1.11 cache.inc
--- includes/cache.inc	12 May 2007 18:26:15 -0000	1.11
+++ includes/cache.inc	17 May 2007 06:23:47 -0000
@@ -104,12 +104,10 @@
     $data = serialize($data);
     $serialized = 1;
   }
-  db_lock_table($table);
-  db_query("UPDATE {". $table ."} SET data = %b, created = %d, expire = %d, headers = '%s', serialized = %d WHERE cid = '%s'", $data, time(), $expire, $headers, $serialized, $cid);
-  if (!db_affected_rows()) {
-    @db_query("INSERT INTO {". $table ."} (cid, data, created, expire, headers, serialized) VALUES ('%s', %b, %d, %d, '%s', %d)", $cid, $data, time(), $expire, $headers, $serialized);
-  }
-  db_unlock_tables();
+  db_query_replace(
+    array("DELETE FROM {%s} WHERE cid = '%s'", $table, $cid),
+    array("INSERT INTO {%s} (cid, data, created, expire, headers) VALUES ('%s', %b, %d, %d, '%s')", $table, $cid, $data, time(), $expire, $headers)
+  );
 }
 
 /**
Index: includes/database.mysql.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/database.mysql.inc,v
retrieving revision 1.71
diff -u -r1.71 database.mysql.inc
--- includes/database.mysql.inc	8 May 2007 16:36:55 -0000	1.71
+++ includes/database.mysql.inc	17 May 2007 06:23:47 -0000
@@ -248,13 +248,22 @@
  * with table prefixes. For example, db_next_id('{node}_nid');
  */
 function db_next_id($name) {
+  // Prefix any curly-bracket "{table}" names
   $name = db_prefix_tables($name);
-  db_query('LOCK TABLES {sequences} WRITE');
-  $id = db_result(db_query("SELECT id FROM {sequences} WHERE name = '%s'", $name)) + 1;
-  db_query("REPLACE INTO {sequences} VALUES ('%s', %d)", $name, $id);
-  db_query('UNLOCK TABLES');
-
-  return $id;
+  // Assume initially that the sequence already exists.  Attempt to update it atomically.
+  // LAST_INSERT_ID lets us get its value later. IGNORE suppresses update failures.
+  db_query("UPDATE IGNORE {sequences} SET id=LAST_INSERT_ID(id + 1) WHERE name = '%s'", $name);
+  // Check whether that worked
+  if (!db_affected_rows()) {
+    // Updated failed, so the sequence doesn't exist yet.
+    // In either case, try to create a new sequence starting from zero
+    // IGNORE suppresses insert error if e.g. a concurrent process got there first.
+    db_query("INSERT IGNORE INTO {sequences} VALUES ('%s', %d)", $name, 0);
+    // Sequence now exists (unless some database error occurred to prevent it)
+    // Retry update, allowing for possible concurrent process. It should work this time.
+    db_query("UPDATE {sequences} SET id = LAST_INSERT_ID(id + 1) WHERE name = '%s'", $name);
+  }
+  return mysql_insert_id();
 }
 
 /**
@@ -435,7 +444,20 @@
 }
 
 /**
+ * Perform a replace query.
+ *
+ * @param $delete
+ *   An array, where the first value is a query which deletes one row,
+ *   subsequent values are arguments. Same syntax as of db_query.
+ * @param
+ *   An array, where the first value is a query which inserts the new row,
+ *   subsequent values are arguments. Same syntax as of db_query.
+ */
+function db_query_replace($delete, $insert) {
+  $insert_query = array_shift($insert);
+  db_query(preg_replace('/^INSERT /', 'REPLACE ', $insert_query), $insert);
+}
+
+/**
  * @} End of "ingroup database".
  */
-
-
Index: includes/database.mysqli.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/database.mysqli.inc,v
retrieving revision 1.35
diff -u -r1.35 database.mysqli.inc
--- includes/database.mysqli.inc	21 Apr 2007 18:08:41 -0000	1.35
+++ includes/database.mysqli.inc	17 May 2007 06:23:47 -0000
@@ -239,13 +239,22 @@
  * with table prefixes. For example, db_next_id('{node}_nid');
  */
 function db_next_id($name) {
+  // Prefix any curly-bracket "{table}" names
   $name = db_prefix_tables($name);
-  db_query('LOCK TABLES {sequences} WRITE');
-  $id = db_result(db_query("SELECT id FROM {sequences} WHERE name = '%s'", $name)) + 1;
-  db_query("REPLACE INTO {sequences} VALUES ('%s', %d)", $name, $id);
-  db_query('UNLOCK TABLES');
-
-  return $id;
+  // Assume initially that the sequence already exists.  Attempt to update it atomically.
+  // LAST_INSERT_ID lets us get its value later. IGNORE suppresses update failures.
+  db_query("UPDATE IGNORE {sequences} SET id=LAST_INSERT_ID(id + 1) WHERE name = '%s'", $name);
+  // Check whether that worked
+  if (!db_affected_rows()) {
+    // Updated failed, so the sequence doesn't exist yet.
+    // In either case, try to create a new sequence starting from zero
+    // IGNORE suppresses insert error if e.g. a concurrent process got there first.
+    db_query("INSERT IGNORE INTO {sequences} VALUES ('%s', %d)", $name, 0);
+    // Sequence now exists (unless some database error occurred to prevent it)
+    // Retry update, allowing for possible concurrent process. It should work this time.
+    db_query("UPDATE {sequences} SET id = LAST_INSERT_ID(id + 1) WHERE name = '%s'", $name);
+  }
+  return mysqli_insert_id();
 }
 
 /**
@@ -426,6 +435,21 @@
 }
 
 /**
+ * Perform a replace query.
+ *
+ * @param $delete
+ *   An array, where the first value is a query which deletes one row,
+ *   subsequent values are arguments. Same syntax as of db_query.
+ * @param
+ *   An array, where the first value is a query which inserts the new row,
+ *   subsequent values are arguments. Same syntax as of db_query.
+ */
+function db_query_replace($delete, $insert) {
+  $insert_query = array_shift($insert);
+  db_query(preg_replace('/^INSERT /', 'REPLACE ', $insert_query), $insert);
+}
+
+/**
  * @} End of "ingroup database".
  */
 
Index: includes/database.pgsql.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/database.pgsql.inc,v
retrieving revision 1.45
diff -u -r1.45 database.pgsql.inc
--- includes/database.pgsql.inc	21 Apr 2007 18:08:41 -0000	1.45
+++ includes/database.pgsql.inc	17 May 2007 06:23:47 -0000
@@ -433,6 +433,26 @@
 }
 
 /**
+ * Perform a replace query.
+ *
+ * @param $delete
+ *   An array, where the first value is a query which deletes one row,
+ *   subsequent values are arguments. Same syntax as of db_query.
+ * @param
+ *   An array, where the first value is a query which inserts the new row,
+ *   subsequent values are arguments. Same syntax as of db_query.
+ */
+function db_query_replace($delete, $insert) {
+  $delete_query = array_shift($delete);
+  db_query('BEGIN');
+  db_query(preg_replace('/^DELETE /', 'SELECT ', $delete_query .' FOR UPDATE'), $delete);
+  db_query($delete_query, $delete);
+  $insert_query = array_shift($insert);
+  db_query($insert_query, $insert);
+  db_query('COMMIT');
+}
+
+/**
  * @} End of "ingroup database".
  */