support for redirection of read only queries to a round robbin of rea…

…d db handles

config/globalConfig.xsm

@@ -25,13 +25,15 @@
             <VAR name="defaultLocale"       value = "en_US" desc = "default locale for site" />
             <VAR name="useClientLocale"     value = "true"  desc = "when true, SiteManager will default to the locale requested by the clients browser, if available" />
         </SECTION>
+        <!--
         <SECTION name="db" id="default">
             <VAR name="active"              value = "false" desc = "whether this connection is active or not" />
             <VAR name="defaultConnection"   value = "true"  desc = "set to true to have this connection be the default connection. will be $dbH" />
             <VAR name="dbType"              value = "mysql" desc = "the database type. must be valid PEAR database type." />
             <VAR name="persistent"          value = "true"  desc = "bool to determine whether this is a persistent connection or not" />
             <VAR name="required"            value = "true"  desc = "if this is true, a fatal error will be thrown if the connection fails. if false, it will ignore a bad connection." />
         </SECTION>
+        -->
         <SECTION name="memcached" id="default">
             <VAR name="host"            value = "localhost"  desc = "memcached host" />
             <VAR name="port"            value = "11211"  desc = "memcached port" />

lib/smDbWrapper.inc

@@ -61,13 +61,25 @@ class SM_dbWrapper
     /**
      * simple counter
      */
-    public $queryCount = 0;
+    static public $queryCount = 0;
+    static public $readCount = 0;
 
     /**
      * read only database connection: only allow SELECT
      */
     public $readOnly = false;
 
+    /**
+     * a list of db handles we redirect SELECT queries to. it will rotate through
+     * the list in round robin fashion
+     */
+    public $roList = NULL;
+
+    /**
+     * last index we sent a query to in roList
+     */
+    public $roI = 0;
+
     function __construct($id, $dsn, $user = NULL, $pass = NULL, $options = NULL) {
         $this->SM_id = $id;
         $this->config['dsn'] = $dsn;
@@ -177,12 +189,25 @@ class SM_dbWrapper
         // so that siteManager knows the last ID in use
         $GLOBALS['SM_LAST_DB_ID'] = $this->SM_id;
 
-        $this->queryCount++;
-
-        // XXX we're strict here and require the first word to be SELECT.
-        // this is to avoid multiple queries in one string
-        if ($this->readOnly && strtoupper(substr($query,0,6)) != 'SELECT') {
-            SM_fatalErrorPage('ro db violation: '.substr($query,0,3));
+        self::$queryCount++;
+
+        // we're strict here and require the first word to be SELECT (no leading spaces)
+        // this avoids failing ro check on multiple queries in one string
+        if ($this->readOnly || $this->roList) {
+            $isSelect = (($query[0] == 'S' || $query[0] == 's') && ($query[1] == 'E' || $query[1] == 'e'));
+            if ($isSelect)
+                self::$readCount++;
+            // read only check
+            if ($this->readOnly && !$isSelect) {
+                SM_fatalErrorPage('ro db violation: '.substr($query,0,2));
+            }
+            // round robin read only redirects
+            elseif ($this->roList && $isSelect) {
+                $result = $this->roList[$this->roI]->query($query);
+                if (sizeof($this->roList) > 1)
+                    $this->roI = ($this->roI + 1) % sizeof($this->roList);
+                return $result;
+            }
         }
 
         // unless we're benchmarking, just record the last query (for errors) and go to parent

lib/smObject.inc

@@ -594,10 +594,10 @@ class SM_dbHandles implements ArrayAccess {
     // db settings to connect lazily (i.e., on first use)
     public $lazyConnect = array();
 
-    public function offsetGet($i) {
+    public function offsetGet($i,$fatal=true) {
         // if the handle they are looking for isn't defined,
         // see if it's a lazyConnect and if so, make the connection
-            global $SM_siteManager;
+        global $SM_siteManager;
         if (empty($this->data[$i])) {
             if (isset($this->lazyConnect[$i])) {
                 // do lazy connect
@@ -606,14 +606,15 @@ class SM_dbHandles implements ArrayAccess {
             }
             else {
                 // no lazy connect, it really doesn't exist
-                $SM_siteManager->fatalErrorPage('database connection undefined: '.$id);
+                if ($fatal)
+                    $SM_siteManager->fatalErrorPage('database connection undefined: '.$id);
             }
         }
         return $this->data[$i];
     }
 
     public function offsetExists ($i) {
-        $d = $this->offsetGet($i);
+        $d = $this->offsetGet($i,false);
         return !empty($d);
     }
 

lib/smRoot.inc

@@ -663,8 +663,23 @@ class SM_siteManagerRoot extends SM_object {
                                                 $dbSettings['userName'],
                                                 $dbSettings['passWord'],
                                                 array(PDO::ATTR_PERSISTENT => $dbSettings['persistent']));
+            $this->debugLog("added database connection [$id]");
             if ($dbSettings['readOnly'])
                 $this->dbHL[$id]->readOnly = true;
+            if ($dbSettings['readRedirect']) {
+                if ($this->dbHL[$id]->readOnly)
+                    $this->fatalErrorPage('cannot be readOnly and readRedirect');
+                // this db handle will redirect SELECTs to one or more other handles (which are presumably readOnly)
+                // these must have already been defined
+                $rList = explode(',',$dbSettings['readRedirect']);
+                foreach ($rList as $roid) {
+                    if (!isset($this->dbHL[$roid]))
+                        $this->fatalErrorPage('undefined readRedirect id: '.$roid);
+                    if (!$this->dbHL[$roid]->readOnly)
+                        $this->fatalErrorPage('readRedirect connection is not read only: '.$roid);
+                    $this->dbHL[$id]->roList[] =& $this->dbHL[$roid];
+                }
+            }
         } catch (PDOException $e) {
             if ($dieOnError) {
                 $this->debugLog($e->getMessage()."<br />\n");
@@ -905,7 +920,7 @@ class SM_siteManagerRoot extends SM_object {
         if ($this->siteConfig->getVar('flags','showLoadTime')) {
             if ($GLOBALS['SM_develState']) {
                 $mem = memory_get_peak_usage();
-                echo "\n<!-- $scriptLoadTime secs / $mem bytes / {$this->dbH->queryCount} queries -->\n";
+                echo "\n<!-- $scriptLoadTime secs / $mem bytes / ".SM_dbWrapper::$queryCount." (".SM_dbWrapper::$readCount." read) queries -->\n";
             }
             else {
                 echo "\n<!-- $scriptLoadTime s -->\n";