Index: database.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/database.inc,v
retrieving revision 1.69
diff -u -r1.69 database.inc
--- database.inc	25 May 2007 12:46:43 -0000	1.69
+++ database.inc	27 May 2007 07:52:11 -0000
@@ -115,8 +115,8 @@
  * @return the name of the previously active database or FALSE if non was found.
  */
 function db_set_active($name = 'default') {
-  global $db_url, $db_type, $active_db;
-  static $db_conns;
+  global $db_url, $db_slave_url, $db_type, $active_db, $active_slave_db;
+  static $db_conns, $db_slave_conns;
 
   if (empty($db_url)) {
     include_once 'includes/install.inc';
@@ -124,12 +124,31 @@
   }
 
   if (!isset($db_conns[$name])) {
-    // Initiate a new connection, using the named DB URL specified.
+    // If the $name doesn't have a corresponding URL, use the default.
+    if (!isset($db_url[$name])) {
+      $name = 'default';
+    }
+    
+    // Initiate a new connection, using the specifed DB URL.
     if (is_array($db_url)) {
-      $connect_url = array_key_exists($name, $db_url) ? $db_url[$name] : $db_url['default'];
+      $connect_url = $db_url[$name];
+      if (is_array($db_slave_url[$name])) {
+        $slave_index = mt_rand(0, count($db_slave_url[$name]));
+        $slave_connect_url = $db_slave_url[$name][$slave_index];
+      }
+      else {
+        $slave_connect_url = $db_slave_url[$name];        
+      }
     }
     else {
       $connect_url = $db_url;
+      if (is_array($db_slave_url)) {
+        $slave_index = mt_rand(0, count($db_slave_url));
+        $slave_connect_url = $db_slave_url[$slave_index];
+      }
+      else {
+        $slave_connect_url = $db_slave_url;        
+      }
     }
 
     $db_type = substr($connect_url, 0, strpos($connect_url, '://'));
@@ -147,11 +166,20 @@
     }
 
     $db_conns[$name] = db_connect($connect_url);
+    if (empty($slave_connect_url)) {
+      $db_slave_conns[$name] = db_connect($slave_connect_url); 
+    }
   }
 
   $previous_db = $active_db;
-  // Set the active connection.
+  // Set the active connections.
   $active_db = $db_conns[$name];
+  if (isset($db_slave_conns[$name])) {
+    $active_slave_db = $db_slave_conns[$name];
+  }
+  else {
+    unset($active_slave_db);
+  }
 
   return array_search($previous_db, $db_conns);
 }
@@ -222,6 +250,42 @@
 }
 
 /**
+ * Runs a basic, read-only query in the active slave database.
+ *
+ * User-supplied arguments to the query should be passed in as separate
+ * parameters so that they can be properly escaped to avoid SQL injection
+ * attacks.
+ *
+ * @param $query
+ *   A string containing an SQL query.
+ * @param ...
+ *   A variable number of arguments which are substituted into the query
+ *   using printf() syntax. Instead of a variable number of query arguments,
+ *   you may also pass a single array containing the query arguments.
+ *
+ *   Valid %-modifiers are: %s, %d, %f, %b (binary data, do not enclose
+ *   in '') and %%.
+ *
+ *   NOTE: using this syntax will cast NULL and FALSE values to decimal 0,
+ *   and TRUE values to decimal 1.
+ *
+ * @return
+ *   A database query result resource, or FALSE if the query was not
+ *   executed correctly.
+ */
+function db_query_read_only($query) {
+  $args = func_get_args();
+  array_shift($args);
+  $query = db_prefix_tables($query);
+  if (isset($args[0]) and is_array($args[0])) { // 'All arguments in one array' syntax
+    $args = $args[0];
+  }
+  _db_query_callback($args, TRUE);
+  $query = preg_replace_callback(DB_QUERY_REGEXP, '_db_query_callback', $query);
+  return _db_query($query, 0, TRUE);
+}
+
+/**
  * Helper function for db_rewrite_sql.
  *
  * Collects JOIN and WHERE statements via hook_db_rewrite_sql()
Index: database.mysql.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/database.mysql.inc,v
retrieving revision 1.73
diff -u -r1.73 database.mysql.inc
--- database.mysql.inc	25 May 2007 21:01:30 -0000	1.73
+++ database.mysql.inc	27 May 2007 07:52:11 -0000
@@ -133,15 +133,20 @@
 /**
  * Helper function for db_query().
  */
-function _db_query($query, $debug = 0) {
-  global $active_db, $queries;
+function _db_query($query, $debug = 0, $read_only = FALSE) {
+  global $active_db, $active_slave_db, $queries;
 
   if (variable_get('dev_query', 0)) {
     list($usec, $sec) = explode(' ', microtime());
     $timer = (float)$usec + (float)$sec;
   }
 
-  $result = mysql_query($query, $active_db);
+  if (isset($active_slave_db) && ($read_only || strtoupper(substr($query, 0, 6)) == 'SELECT')) {
+    $result = mysql_query($active_slave_db, $query);    
+  }
+  else {
+    $result = mysql_query($active_db, $query);
+  }
 
   if (variable_get('dev_query', 0)) {
     $bt = debug_backtrace();
@@ -310,6 +315,50 @@
 }
 
 /**
+ * Runs a limited-range, read-only query in the active slave database.
+ *
+ * Use this as a substitute for db_query() when a subset of the query is to be
+ * returned.
+ * User-supplied arguments to the query should be passed in as separate parameters
+ * so that they can be properly escaped to avoid SQL injection attacks.
+ *
+ * @param $query
+ *   A string containing an SQL query.
+ * @param ...
+ *   A variable number of arguments which are substituted into the query
+ *   using printf() syntax. The query arguments can be enclosed in one
+ *   array instead.
+ *   Valid %-modifiers are: %s, %d, %f, %b (binary data, do not enclose
+ *   in '') and %%.
+ *
+ *   NOTE: using this syntax will cast NULL and FALSE values to decimal 0,
+ *   and TRUE values to decimal 1.
+ *
+ * @param $from
+ *   The first result row to return.
+ * @param $count
+ *   The maximum number of result rows to return.
+ * @return
+ *   A database query result resource, or FALSE if the query was not executed
+ *   correctly.
+ */
+function db_query_range_read_only($query) {
+  $args = func_get_args();
+  $count = array_pop($args);
+  $from = array_pop($args);
+  array_shift($args);
+
+  $query = db_prefix_tables($query);
+  if (isset($args[0]) and is_array($args[0])) { // 'All arguments in one array' syntax
+    $args = $args[0];
+  }
+  _db_query_callback($args, TRUE);
+  $query = preg_replace_callback(DB_QUERY_REGEXP, '_db_query_callback', $query);
+  $query .= ' LIMIT '. (int)$from .', '. (int)$count;
+  return _db_query($query, 0, TRUE);
+}
+
+/**
  * Runs a SELECT query and stores its results in a temporary table.
  *
  * Use this as a substitute for db_query() when the results need to stored
Index: database.mysqli.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/database.mysqli.inc,v
retrieving revision 1.37
diff -u -r1.37 database.mysqli.inc
--- database.mysqli.inc	25 May 2007 21:01:30 -0000	1.37
+++ database.mysqli.inc	27 May 2007 07:52:12 -0000
@@ -124,15 +124,20 @@
 /**
  * Helper function for db_query().
  */
-function _db_query($query, $debug = 0) {
-  global $active_db, $queries;
+function _db_query($query, $debug = 0, $read_only = FALSE) {
+  global $active_db, $active_slave_db, $queries;
 
   if (variable_get('dev_query', 0)) {
     list($usec, $sec) = explode(' ', microtime());
     $timer = (float)$usec + (float)$sec;
   }
 
-  $result = mysqli_query($active_db, $query);
+  if (isset($active_slave_db) && ($read_only || strtoupper(substr($query, 0, 6)) == 'SELECT')) {
+    $result = mysqli_query($active_slave_db, $query);    
+  }
+  else {
+    $result = mysqli_query($active_db, $query);
+  }
 
   if (variable_get('dev_query', 0)) {
     $bt = debug_backtrace();
@@ -301,6 +306,51 @@
   return _db_query($query);
 }
 
+
+/**
+ * Runs a limited-range, read-only query in the active slave database.
+ *
+ * Use this as a substitute for db_query() when a subset of the query is to be
+ * returned.
+ * User-supplied arguments to the query should be passed in as separate parameters
+ * so that they can be properly escaped to avoid SQL injection attacks.
+ *
+ * @param $query
+ *   A string containing an SQL query.
+ * @param ...
+ *   A variable number of arguments which are substituted into the query
+ *   using printf() syntax. The query arguments can be enclosed in one
+ *   array instead.
+ *   Valid %-modifiers are: %s, %d, %f, %b (binary data, do not enclose
+ *   in '') and %%.
+ *
+ *   NOTE: using this syntax will cast NULL and FALSE values to decimal 0,
+ *   and TRUE values to decimal 1.
+ *
+ * @param $from
+ *   The first result row to return.
+ * @param $count
+ *   The maximum number of result rows to return.
+ * @return
+ *   A database query result resource, or FALSE if the query was not executed
+ *   correctly.
+ */
+function db_query_range_read_only($query) {
+  $args = func_get_args();
+  $count = array_pop($args);
+  $from = array_pop($args);
+  array_shift($args);
+
+  $query = db_prefix_tables($query);
+  if (isset($args[0]) and is_array($args[0])) { // 'All arguments in one array' syntax
+    $args = $args[0];
+  }
+  _db_query_callback($args, TRUE);
+  $query = preg_replace_callback(DB_QUERY_REGEXP, '_db_query_callback', $query);
+  $query .= ' LIMIT '. (int)$from .', '. (int)$count;
+  return _db_query($query, 0, TRUE);
+}
+
 /**
  * Runs a SELECT query and stores its results in a temporary table.
  *
Index: database.pgsql.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/database.pgsql.inc,v
retrieving revision 1.46
diff -u -r1.46 database.pgsql.inc
--- database.pgsql.inc	25 May 2007 12:46:43 -0000	1.46
+++ database.pgsql.inc	27 May 2007 07:52:12 -0000
@@ -114,15 +114,20 @@
 /**
  * Helper function for db_query().
  */
-function _db_query($query, $debug = 0) {
-  global $active_db, $last_result, $queries;
+function _db_query($query, $debug = 0, $read_only = FALSE) {
+  global $active_db, $active_slave_db, $last_result, $queries;
 
   if (variable_get('dev_query', 0)) {
     list($usec, $sec) = explode(' ', microtime());
     $timer = (float)$usec + (float)$sec;
   }
 
-  $last_result = pg_query($active_db, $query);
+  if (isset($active_slave_db) && ($read_only || strtoupper(substr($query, 0, 6)) == 'SELECT')) {
+    $result = pg_query($active_slave_db, $query);    
+  }
+  else {
+    $result = pg_query($active_db, $query);
+  }
 
   if (variable_get('dev_query', 0)) {
     $bt = debug_backtrace();
@@ -291,6 +296,51 @@
 }
 
 /**
+ * Runs a limited-range, read-only query in the active slave database.
+ *
+ * Use this as a substitute for db_query() when a subset of the query
+ * is to be returned.
+ * User-supplied arguments to the query should be passed in as separate
+ * parameters so that they can be properly escaped to avoid SQL injection
+ * attacks.
+ *
+ * @param $query
+ *   A string containing an SQL query.
+ * @param ...
+ *   A variable number of arguments which are substituted into the query
+ *   using printf() syntax. Instead of a variable number of query arguments,
+ *   you may also pass a single array containing the query arguments.
+ *   Valid %-modifiers are: %s, %d, %f, %b (binary data, do not enclose
+ *   in '') and %%.
+ *
+ *   NOTE: using this syntax will cast NULL and FALSE values to decimal 0,
+ *   and TRUE values to decimal 1.
+ *
+ * @param $from
+ *   The first result row to return.
+ * @param $count
+ *   The maximum number of result rows to return.
+ * @return
+ *   A database query result resource, or FALSE if the query was not executed
+ *   correctly.
+ */
+function db_query_range_read_only($query) {
+  $args = func_get_args();
+  $count = array_pop($args);
+  $from = array_pop($args);
+  array_shift($args);
+
+  $query = db_prefix_tables($query);
+  if (isset($args[0]) and is_array($args[0])) { // 'All arguments in one array' syntax
+    $args = $args[0];
+  }
+  _db_query_callback($args, TRUE);
+  $query = preg_replace_callback(DB_QUERY_REGEXP, '_db_query_callback', $query);
+  $query .= ' LIMIT '. (int)$count .' OFFSET '. (int)$from;
+  return _db_query($query, 0, TRUE);
+}
+
+/**
  * Runs a SELECT query and stores its results in a temporary table.
  *
  * Use this as a substitute for db_query() when the results need to stored