diff --git a/framework/YiiBase.php b/framework/YiiBase.php
index 213b81c..9d3698b 100644
--- a/framework/YiiBase.php
+++ b/framework/YiiBase.php
@@ -8,7 +8,9 @@
  */
 
 use yii\base\Exception;
+use yii\logging\Logger;
 use yii\base\InvalidCallException;
+use yii\base\InvalidConfigException;
 
 /**
  * Gets the application start timestamp.
@@ -394,7 +396,7 @@ class YiiBase
 	public static function trace($message, $category = 'application')
 	{
 		if (YII_DEBUG) {
-			self::getLogger()->trace($message, $category);
+			self::getLogger()->log($message, Logger::LEVEL_TRACE, $category);
 		}
 	}
 
@@ -407,7 +409,7 @@ class YiiBase
 	 */
 	public static function error($message, $category = 'application')
 	{
-		self::getLogger()->error($message, $category);
+		self::getLogger()->log($message, Logger::LEVEL_ERROR, $category);
 	}
 
 	/**
@@ -419,7 +421,7 @@ class YiiBase
 	 */
 	public static function warning($message, $category = 'application')
 	{
-		self::getLogger()->warning($message, $category);
+		self::getLogger()->log($message, Logger::LEVEL_WARNING, $category);
 	}
 
 	/**
@@ -431,7 +433,7 @@ class YiiBase
 	 */
 	public static function info($message, $category = 'application')
 	{
-		self::getLogger()->info($message, $category);
+		self::getLogger()->log($message, Logger::LEVEL_INFO, $category);
 	}
 
 	/**
@@ -453,7 +455,7 @@ class YiiBase
 	 */
 	public static function beginProfile($token, $category = 'application')
 	{
-		self::getLogger()->beginProfile($token, $category);
+		self::getLogger()->log($token, Logger::LEVEL_PROFILE_BEGIN, $category);
 	}
 
 	/**
@@ -465,7 +467,7 @@ class YiiBase
 	 */
 	public static function endProfile($token, $category = 'application')
 	{
-		self::getLogger()->endProfile($token, $category);
+		self::getLogger()->log($token, Logger::LEVEL_PROFILE_END, $category);
 	}
 
 	/**
@@ -477,13 +479,13 @@ class YiiBase
 		if (self::$_logger !== null) {
 			return self::$_logger;
 		} else {
-			return self::$_logger = new \yii\logging\Logger;
+			return self::$_logger = new Logger;
 		}
 	}
 
 	/**
 	 * Sets the logger object.
-	 * @param \yii\logging\Logger $logger the logger object.
+	 * @param Logger $logger the logger object.
 	 */
 	public static function setLogger($logger)
 	{
diff --git a/framework/base/Application.php b/framework/base/Application.php
index e945160..6a20182 100644
--- a/framework/base/Application.php
+++ b/framework/base/Application.php
@@ -75,6 +75,8 @@ use yii\base\InvalidCallException;
  */
 class Application extends Module
 {
+	const EVENT_BEFORE_REQUEST = 'beforeRequest';
+	const EVENT_AFTER_REQUEST = 'afterRequest';
 	/**
 	 * @var string the application name. Defaults to 'My Application'.
 	 */
@@ -178,7 +180,7 @@ class Application extends Module
 	 */
 	public function beforeRequest()
 	{
-		$this->trigger('beforeRequest');
+		$this->trigger(self::EVENT_BEFORE_REQUEST);
 	}
 
 	/**
@@ -186,7 +188,7 @@ class Application extends Module
 	 */
 	public function afterRequest()
 	{
-		$this->trigger('afterRequest');
+		$this->trigger(self::EVENT_AFTER_REQUEST);
 	}
 
 	/**
diff --git a/framework/logging/DbTarget.php b/framework/logging/DbTarget.php
index dc541f5..004bf21 100644
--- a/framework/logging/DbTarget.php
+++ b/framework/logging/DbTarget.php
@@ -9,6 +9,9 @@
 
 namespace yii\logging;
 
+use yii\db\Connection;
+use yii\base\InvalidConfigException;
+
 /**
  * DbTarget stores log messages in a database table.
  *
@@ -23,23 +26,21 @@ namespace yii\logging;
 class DbTarget extends Target
 {
 	/**
-	 * @var string the ID of [[\yii\db\Connection]] application component.
+	 * @var string the ID of [[Connection]] application component.
 	 * Defaults to 'db'. Please make sure that your database contains a table
 	 * whose name is as specified in [[tableName]] and has the required table structure.
 	 * @see tableName
 	 */
 	public $connectionID = 'db';
 	/**
-	 * @var string the name of the DB table that stores log messages. Defaults to '{{log}}'.
-	 * If you are using table prefix 'tbl_' (configured via [[\yii\db\Connection::tablePrefix]]),
-	 * it means the DB table would be named as 'tbl_log'.
+	 * @var string the name of the DB table that stores log messages. Defaults to 'tbl_log'.
 	 *
-	 * The DB table must have the following structure:
+	 * The DB table should have the following structure:
 	 *
 	 * ~~~
 	 * CREATE TABLE tbl_log (
 	 *	   id       INTEGER NOT NULL AUTO_INCREMENT PRIMARY KEY,
-	 *	   level    VARCHAR(32),
+	 *	   level    INTEGER,
 	 *	   category VARCHAR(255),
 	 *	   log_time INTEGER,
 	 *	   message  TEXT,
@@ -50,42 +51,53 @@ class DbTarget extends Target
 	 *
 	 * Note that the 'id' column must be created as an auto-incremental column.
 	 * The above SQL shows the syntax of MySQL. If you are using other DBMS, you need
-	 * to adjust it accordingly. For example, in PosgreSQL, it should be `id SERIAL PRIMARY KEY`.
+	 * to adjust it accordingly. For example, in PostgreSQL, it should be `id SERIAL PRIMARY KEY`.
 	 *
 	 * The indexes declared above are not required. They are mainly used to improve the performance
 	 * of some queries about message levels and categories. Depending on your actual needs, you may
-	 * want to create other indexes.
+	 * want to create additional indexes (e.g. index on log_time).
 	 */
-	public $tableName = '{{log}}';
+	public $tableName = 'tbl_log';
 
 	private $_db;
 
 	/**
 	 * Returns the DB connection used for saving log messages.
-	 * @return \yii\db\Connection the DB connection instance
-	 * @throws \yii\base\Exception if [[connectionID]] does not refer to a valid application component ID.
+	 * @return Connection the DB connection instance
+	 * @throws InvalidConfigException if [[connectionID]] does not point to a valid application component.
 	 */
 	public function getDb()
 	{
 		if ($this->_db === null) {
-			$this->_db = \Yii::$application->getComponent($this->connectionID);
-			if (!$this->_db instanceof \yii\db\Connection) {
-				throw new \yii\base\Exception('DbTarget.connectionID must refer to a valid application component ID');
+			$db = \Yii::$application->getComponent($this->connectionID);
+			if ($db instanceof Connection) {
+				$this->_db = $db;
+			} else {
+				throw new InvalidConfigException("DbTarget::connectionID must refer to the ID of a DB application component.");
 			}
 		}
 		return $this->_db;
 	}
 
 	/**
+	 * Sets the DB connection used by the cache component.
+	 * @param Connection $value the DB connection instance
+	 */
+	public function setDb($value)
+	{
+		$this->_db = $value;
+	}
+
+	/**
 	 * Stores log [[messages]] to DB.
 	 * @param boolean $final whether this method is called at the end of the current application
 	 */
 	public function exportMessages($final)
 	{
-		$sql = "INSERT INTO {$this->tableName}
-			(level, category, log_time, message) VALUES
-			(:level, :category, :log_time, :message)";
-		$command = $this->getDb()->createCommand($sql);
+		$db = $this->getDb();
+		$tableName = $db->quoteTableName($this->tableName);
+		$sql = "INSERT INTO $tableName (level, category, log_time, message) VALUES (:level, :category, :log_time, :message)";
+		$command = $db->createCommand($sql);
 		foreach ($this->messages as $message) {
 			$command->bindValues(array(
 				':level' => $message[1],
diff --git a/framework/logging/FileTarget.php b/framework/logging/FileTarget.php
index 2595ed3..f4ddf44 100644
--- a/framework/logging/FileTarget.php
+++ b/framework/logging/FileTarget.php
@@ -8,17 +8,16 @@
  */
 
 namespace yii\logging;
+use yii\base\InvalidConfigException;
 
 /**
- * FileTarget records log messages in files.
+ * FileTarget records log messages in a file.
  *
- * The log files are stored under [[logPath]] and their name
- * is specified by [[logFile]]. If the size of the log file exceeds
- * [[maxFileSize]] (in kilo-bytes), a rotation will be performed,
- * which renames the current log file by suffixing the file name
- * with '.1'. All existing log files are moved backwards one place,
- * i.e., '.2' to '.3', '.1' to '.2', and so on. The property
- * [[maxLogFiles]] specifies how many files to keep.
+ * The log file is specified via [[logFile]]. If the size of the log file exceeds
+ * [[maxFileSize]] (in kilo-bytes), a rotation will be performed, which renames
+ * the current log file by suffixing the file name with '.1'. All existing log
+ * files are moved backwards by one place, i.e., '.2' to '.3', '.1' to '.2', and so on.
+ * The property [[maxLogFiles]] specifies how many files to keep.
  *
  * @author Qiang Xue <qiang.xue@gmail.com>
  * @since 2.0
@@ -26,6 +25,12 @@ namespace yii\logging;
 class FileTarget extends Target
 {
 	/**
+	 * @var string log file path or path alias. If not set, it means the 'application.log' file under
+	 * the application runtime directory. Please make sure the directory containing
+	 * the log file is writable by the Web server process.
+	 */
+	public $logFile;
+	/**
 	 * @var integer maximum log file size, in kilo-bytes. Defaults to 1024, meaning 1MB.
 	 */
 	public $maxFileSize = 1024; // in KB
@@ -33,14 +38,6 @@ class FileTarget extends Target
 	 * @var integer number of log files used for rotation. Defaults to 5.
 	 */
 	public $maxLogFiles = 5;
-	/**
-	 * @var string directory storing log files. Defaults to the application runtime path.
-	 */
-	public $logPath;
-	/**
-	 * @var string log file name. Defaults to 'application.log'.
-	 */
-	public $logFile = 'application.log';
 
 
 	/**
@@ -50,11 +47,14 @@ class FileTarget extends Target
 	public function init()
 	{
 		parent::init();
-		if ($this->logPath === null) {
-			$this->logPath = \Yii::$application->getRuntimePath();
+		if ($this->logFile === null) {
+			$this->logFile = \Yii::$application->getRuntimePath() . DIRECTORY_SEPARATOR . 'application.log';
+		} else {
+			$this->logFile = \Yii::getAlias($this->logFile);
 		}
-		if (!is_dir($this->logPath) || !is_writable($this->logPath)) {
-			throw new \yii\base\Exception("Directory '{$this->logPath}' does not exist or is not writable.");
+		$logPath = dirname($this->logFile);
+		if (!is_dir($logPath) || !is_writable($logPath)) {
+			throw new InvalidConfigException("Directory '$logPath' does not exist or is not writable.");
 		}
 		if ($this->maxLogFiles < 1) {
 			$this->maxLogFiles = 1;
@@ -70,15 +70,14 @@ class FileTarget extends Target
 	 */
 	public function exportMessages($final)
 	{
-		$logFile = $this->logPath . DIRECTORY_SEPARATOR . $this->logFile;
-		if (@filesize($logFile) > $this->maxFileSize * 1024) {
+		if (@filesize($this->logFile) > $this->maxFileSize * 1024) {
 			$this->rotateFiles();
 		}
 		$messages = array();
 		foreach ($this->messages as $message) {
 			$messages[] = $this->formatMessage($message);
 		}
-		@file_put_contents($logFile, implode('', $messages), FILE_APPEND | LOCK_EX);
+		@file_put_contents($this->logFile, implode('', $messages), FILE_APPEND | LOCK_EX);
 	}
 
 	/**
@@ -86,7 +85,7 @@ class FileTarget extends Target
 	 */
 	protected function rotateFiles()
 	{
-		$file = $this->logPath . DIRECTORY_SEPARATOR . $this->logFile;
+		$file = $this->logFile;
 		for ($i = $this->maxLogFiles; $i > 0; --$i) {
 			$rotateFile = $file . '.' . $i;
 			if (is_file($rotateFile)) {
diff --git a/framework/logging/Logger.php b/framework/logging/Logger.php
index b6fc7da..e1f809f 100644
--- a/framework/logging/Logger.php
+++ b/framework/logging/Logger.php
@@ -10,6 +10,7 @@
 namespace yii\logging;
 
 use yii\base\Event;
+use yii\base\Exception;
 
 /**
  * Logger records logged messages in memory.
@@ -18,8 +19,6 @@ use yii\base\Event;
  * call [[flush()]] to send logged messages to different log targets, such as
  * file, email, Web.
  *
- * Logger provides a set of events for further customization:
- *
  * @author Qiang Xue <qiang.xue@gmail.com>
  * @since 2.0
  */
@@ -30,12 +29,40 @@ class Logger extends \yii\base\Component
 	 */
 	const EVENT_FLUSH = 'flush';
 
-	const LEVEL_ERROR = 'error';
-	const LEVEL_WARNING = 'warning';
-	const LEVEL_INFO = 'info';
-	const LEVEL_TRACE = 'trace';
-	const LEVEL_PROFILE_BEGIN = 'profile-begin';
-	const LEVEL_PROFILE_END = 'profile-end';
+	/**
+	 * Error message level. An error message is one that indicates the abnormal termination of the
+	 * application and may require developer's handling.
+	 */
+	const LEVEL_ERROR = 0x01;
+	/**
+	 * Warning message level. A warning message is one that indicates some abnormal happens but
+	 * the application is able to continue to run. Developers should pay attention to this message.
+	 */
+	const LEVEL_WARNING = 0x02;
+	/**
+	 * Informational message level. An informational message is one that includes certain information
+	 * for developers to review.
+	 */
+	const LEVEL_INFO = 0x04;
+	/**
+	 * Tracing message level. An tracing message is one that reveals the code execution flow.
+	 */
+	const LEVEL_TRACE = 0x08;
+	/**
+	 * Profiling message level. This indicates the message is for profiling purpose.
+	 */
+	const LEVEL_PROFILE = 0x40;
+	/**
+	 * Profiling message level. This indicates the message is for profiling purpose. It marks the
+	 * beginning of a profiling block.
+	 */
+	const LEVEL_PROFILE_BEGIN = 0x50;
+	/**
+	 * Profiling message level. This indicates the message is for profiling purpose. It marks the
+	 * end of a profiling block.
+	 */
+	const LEVEL_PROFILE_END = 0x60;
+
 
 	/**
 	 * @var integer how many messages should be logged before they are flushed from memory and sent to targets.
@@ -52,7 +79,7 @@ class Logger extends \yii\base\Component
 	 * ~~~
 	 * array(
 	 *   [0] => message (mixed)
-	 *   [1] => level (string)
+	 *   [1] => level (integer)
 	 *   [2] => category (string)
 	 *   [3] => timestamp (float, obtained by microtime(true))
 	 * )
@@ -61,85 +88,13 @@ class Logger extends \yii\base\Component
 	public $messages = array();
 
 	/**
-	 * Logs an error message.
-	 * An error message is typically logged when an unrecoverable error occurs
-	 * during the execution of an application.
-	 * @param mixed $message the message to be logged.
-	 * @param string $category the category of the message.
-	 */
-	public function error($message, $category = 'application')
-	{
-		$this->log($message, self::LEVEL_ERROR, $category);
-	}
-
-	/**
-	 * Logs a trace message.
-	 * Trace messages are logged mainly for development purpose to see
-	 * the execution work flow of some code.
-	 * @param mixed $message the message to be logged.
-	 * @param string $category the category of the message.
-	 */
-	public function trace($message, $category = 'application')
-	{
-		$this->log($message, self::LEVEL_TRACE, $category);
-	}
-
-	/**
-	 * Logs a warning message.
-	 * A warning message is typically logged when an error occurs while the execution
-	 * can still continue.
-	 * @param mixed $message the message to be logged.
-	 * @param string $category the category of the message.
-	 */
-	public function warning($message, $category = 'application')
-	{
-		$this->log($message, self::LEVEL_WARNING, $category);
-	}
-
-	/**
-	 * Logs an informative message.
-	 * An informative message is typically logged by an application to keep record of
-	 * something important (e.g. an administrator logs in).
-	 * @param mixed $message the message to be logged.
-	 * @param string $category the category of the message.
-	 */
-	public function info($message, $category = 'application')
-	{
-		$this->log($message, self::LEVEL_INFO, $category);
-	}
-
-	/**
-	 * Marks the beginning of a code block for profiling.
-	 * This has to be matched with a call to [[endProfile()]] with the same category name.
-	 * The begin- and end- calls must also be properly nested.
-	 * @param string $token token for the code block
-	 * @param string $category the category of this log message
-	 * @see endProfile
-	 */
-	public function beginProfile($token, $category = 'application')
-	{
-		$this->log($token, self::LEVEL_PROFILE_BEGIN, $category);
-	}
-
-	/**
-	 * Marks the end of a code block for profiling.
-	 * This has to be matched with a previous call to [[beginProfile()]] with the same category name.
-	 * @param string $token token for the code block
-	 * @param string $category the category of this log message
-	 * @see beginProfile
-	 */
-	public function endProfile($token, $category = 'application')
-	{
-		$this->log($token, self::LEVEL_PROFILE_END, $category);
-	}
-
-	/**
 	 * Logs a message with the given type and category.
 	 * If `YII_DEBUG` is true and `YII_TRACE_LEVEL` is greater than 0, then additional
 	 * call stack information about application code will be appended to the message.
 	 * @param string $message the message to be logged.
-	 * @param string $level the level of the message. This must be one of the following:
-	 * 'trace', 'info', 'warning', 'error', 'profile'.
+	 * @param integer $level the level of the message. This must be one of the following:
+	 * `Logger::LEVEL_ERROR`, `Logger::LEVEL_WARNING`, `Logger::LEVEL_INFO`, `Logger::LEVEL_TRACE`,
+	 * `Logger::LEVEL_PROFILE_BEGIN`, `Logger::LEVEL_PROFILE_END`.
 	 * @param string $category the category of the message.
 	 */
 	public function log($message, $level, $category = 'application')
@@ -242,14 +197,14 @@ class Logger extends \yii\base\Component
 
 		$stack = array();
 		foreach ($this->messages as $log) {
-			if ($log[1] === self::LEVEL_PROFILE_BEGIN) {
+			list($token, $level, $category, $timestamp) = $log;
+			if ($level == self::LEVEL_PROFILE_BEGIN) {
 				$stack[] = $log;
-			} elseif ($log[1] === self::LEVEL_PROFILE_END) {
-				list($token, $level, $category, $timestamp) = $log;
+			} elseif ($level == self::LEVEL_PROFILE_END) {
 				if (($last = array_pop($stack)) !== null && $last[0] === $token) {
 					$timings[] = array($token, $category, $timestamp - $last[3]);
 				} else {
-					throw new \yii\base\Exception("Unmatched profiling block: $token");
+					throw new Exception("Unmatched profiling block: $token");
 				}
 			}
 		}
diff --git a/framework/logging/Router.php b/framework/logging/Router.php
index ba04b46..aaac8f8 100644
--- a/framework/logging/Router.php
+++ b/framework/logging/Router.php
@@ -9,6 +9,10 @@
 
 namespace yii\logging;
 
+use Yii;
+use yii\base\Component;
+use yii\base\Application;
+
 /**
  * Router manages [[Target|log targets]] that record log messages in different media.
  *
@@ -48,17 +52,17 @@ namespace yii\logging;
  * as follows:
  *
  * ~~~
- * \Yii::$application->log->targets['file']->enabled = false;
+ * Yii::$application->log->targets['file']->enabled = false;
  * ~~~
  *
  * @author Qiang Xue <qiang.xue@gmail.com>
  * @since 2.0
  */
-class Router extends \yii\base\ApplicationComponent
+class Router extends Component
 {
 	/**
 	 * @var Target[] list of log target objects or configurations. If the latter, target objects will
-	 * be created in [[init()]] by calling [[\Yii::createObject()]] with the corresponding object configuration.
+	 * be created in [[init()]] by calling [[Yii::createObject()]] with the corresponding object configuration.
 	 */
 	public $targets = array();
 
@@ -74,28 +78,28 @@ class Router extends \yii\base\ApplicationComponent
 
 		foreach ($this->targets as $name => $target) {
 			if (!$target instanceof Target) {
-				$this->targets[$name] = \Yii::createObject($target);
+				$this->targets[$name] = Yii::createObject($target);
 			}
 		}
 
-		\Yii::getLogger()->on('flush', array($this, 'processMessages'));
-		if (\Yii::$application !== null) {
-			\Yii::$application->on('afterRequest', array($this, 'processMessages'));
+		Yii::getLogger()->on(Logger::EVENT_FLUSH, array($this, 'processMessages'));
+		if (Yii::$application !== null) {
+			Yii::$application->on(Application::EVENT_AFTER_REQUEST, array($this, 'processMessages'));
 		}
 	}
 
 	/**
 	 * Retrieves and processes log messages from the system logger.
 	 * This method mainly serves the event handler to [[Logger::onFlush]]
-	 * and [[\yii\base\Application::onEndRequest]] events.
-	 * It will retrieve the available log messages from the [[\Yii::getLogger|system logger]]
+	 * and [[Application::onEndRequest]] events.
+	 * It will retrieve the available log messages from the [[Yii::getLogger|system logger]]
 	 * and invoke the registered [[targets|log targets]] to do the actual processing.
 	 * @param \yii\base\Event $event event parameter
 	 */
 	public function processMessages($event)
 	{
-		$messages = \Yii::getLogger()->messages;
-		$final = $event->name !== 'flush';
+		$messages = Yii::getLogger()->messages;
+		$final = $event->name === Application::EVENT_AFTER_REQUEST;
 		foreach ($this->targets as $target) {
 			if ($target->enabled) {
 				$target->processMessages($messages, $final);
diff --git a/framework/logging/Target.php b/framework/logging/Target.php
index cda12df..a4e7714 100644
--- a/framework/logging/Target.php
+++ b/framework/logging/Target.php
@@ -9,6 +9,8 @@
 
 namespace yii\logging;
 
+use yii\base\InvalidConfigException;
+
 /**
  * Target is the base class for all log target classes.
  *
@@ -20,6 +22,8 @@ namespace yii\logging;
  * satisfying both filter conditions will be handled. Additionally, you
  * may specify [[except]] to exclude messages of certain categories.
  *
+ * @property integer $levels the message levels that this target is interested in.
+ *
  * @author Qiang Xue <qiang.xue@gmail.com>
  * @since 2.0
  */
@@ -30,10 +34,6 @@ abstract class Target extends \yii\base\Component
 	 */
 	public $enabled = true;
 	/**
-	 * @var array list of message levels that this target is interested in. Defaults to empty, meaning all levels.
-	 */
-	public $levels = array();
-	/**
 	 * @var array list of message categories that this target is interested in. Defaults to empty, meaning all categories.
 	 * You can use an asterisk at the end of a category so that the category may be used to
 	 * match those categories sharing the same common prefix. For example, 'yii\db\*' will match
@@ -70,17 +70,19 @@ abstract class Target extends \yii\base\Component
 	 */
 	public $logVars = array('_GET', '_POST', '_FILES', '_COOKIE', '_SESSION', '_SERVER');
 	/**
-	 * @var boolean whether this target should export the collected messages to persistent storage
-	 * (e.g. DB, email) whenever [[processMessages()]] is called. Defaults to true. If false,
-	 * the collected messages will be stored in [[messages]] without any further processing.
+	 * @var integer how many messages should be accumulated before they are exported.
+	 * Defaults to 1000. Note that messages will always be exported when the application terminates.
+	 * Set this property to be 0 if you don't want to export messages until the application terminates.
 	 */
-	public $autoExport = true;
+	public $exportInterval = 1000;
 	/**
 	 * @var array the messages that are retrieved from the logger so far by this log target.
 	 * @see autoExport
 	 */
 	public $messages = array();
 
+	private $_levels = 0;
+
 	/**
 	 * Exports log messages to a specific destination.
 	 * Child classes must implement this method. Note that you may need
@@ -102,7 +104,8 @@ abstract class Target extends \yii\base\Component
 		$messages = $this->filterMessages($messages);
 		$this->messages = array_merge($this->messages, $messages);
 
-		if (!empty($this->messages) && ($this->autoExport || $final)) {
+		$count = count($this->messages);
+		if ($count > 0 && ($final || $this->exportInterval > 0 && $count >= $this->exportInterval)) {
 			$this->prepareExport($final);
 			$this->exportMessages($final);
 			$this->messages = array();
@@ -160,6 +163,58 @@ abstract class Target extends \yii\base\Component
 	}
 
 	/**
+	 * @return integer the message levels that this target is interested in. This is a bitmap of
+	 * level values. Defaults to 0, meaning all available levels.
+	 */
+	public function getLevels()
+	{
+		return $this->_levels;
+	}
+
+	/**
+	 * Sets the message levels that this target is interested in.
+	 *
+	 * The parameter can be either an array of interested level names or an integer representing
+	 * the bitmap of the interested level values. Valid level names include: 'error',
+	 * 'warning', 'info', 'trace' and 'profile'; valid level values include:
+	 * [[Logger::LEVEL_ERROR]], [[Logger::LEVEL_WARNING]], [[Logger::LEVEL_INFO]],
+	 * [[Logger::LEVEL_TRACE]] and [[Logger::LEVEL_PROFILE]].
+	 *
+	 * For example,
+	 *
+	 * ~~~
+	 * array('error', 'warning')
+	 * // which is equivalent to:
+	 * Logger::LEVEL_ERROR | Logger::LEVEL_WARNING
+	 * ~~~
+	 *
+	 * @param array|integer $levels message levels that this target is interested in.
+	 * @throws InvalidConfigException if an unknown level name is given
+	 */
+	public function setLevels($levels)
+	{
+		static $levelMap = array(
+			'error' => Logger::LEVEL_ERROR,
+			'warning' => Logger::LEVEL_WARNING,
+			'info' => Logger::LEVEL_INFO,
+			'trace' => Logger::LEVEL_TRACE,
+			'profile' => Logger::LEVEL_PROFILE,
+		);
+		if (is_array($levels)) {
+			$this->_levels = 0;
+			foreach ($levels as $level) {
+				if (isset($levelMap[$level])) {
+					$this->_levels |= $levelMap[$level];
+				} else {
+					throw new InvalidConfigException("Unrecognized level: $level");
+				}
+			}
+		} else {
+			$this->_levels = $levels;
+		}
+	}
+
+	/**
 	 * Filters the given messages according to their categories and levels.
 	 * @param array $messages messages to be filtered
 	 * @return array the filtered messages.
@@ -168,8 +223,10 @@ abstract class Target extends \yii\base\Component
 	 */
 	protected function filterMessages($messages)
 	{
+		$levels = $this->getLevels();
+
 		foreach ($messages as $i => $message) {
-			if (!empty($this->levels) && !in_array($message[1], $this->levels)) {
+			if ($levels && !($levels & $message[1])) {
 				unset($messages[$i]);
 				continue;
 			}
@@ -210,7 +267,19 @@ abstract class Target extends \yii\base\Component
 	 */
 	public function formatMessage($message)
 	{
-		$s = is_string($message[0]) ? $message[0] : var_export($message[0], true);
-		return date('Y/m/d H:i:s', $message[3]) . " [{$message[1]}] [{$message[2]}] $s\n";
+		static $levels = array(
+			Logger::LEVEL_ERROR => 'error',
+			Logger::LEVEL_WARNING => 'warning',
+			Logger::LEVEL_INFO => 'info',
+			Logger::LEVEL_TRACE => 'trace',
+			Logger::LEVEL_PROFILE_BEGIN => 'profile begin',
+			Logger::LEVEL_PROFILE_END => 'profile end',
+		);
+		list($text, $level, $category, $timestamp) = $message;
+		$level = isset($levels[$level]) ? $levels[$level] : 'unknown';
+		if (!is_string($text)) {
+			$text = var_export($text, true);
+		}
+		return date('Y/m/d H:i:s', $timestamp) . " [$level] [$category] $text\n";
 	}
 }
diff --git a/todo.md b/todo.md
index 777c57b..0c21fe2 100644
--- a/todo.md
+++ b/todo.md
@@ -1,6 +1,18 @@
+- db
+	* pgsql, sql server, oracle, db2 drivers
+	  * write a guide on creating own schema definitions
+	* document-based (should allow storage-specific methods additionally to generic ones)
+	  * mongodb (put it under framework/db/mongodb)
+	* key-value-based (should allow storage-specific methods additionally to generic ones)
+	  * redis (put it under framework/db/redis or perhaps framework/caching?)
 - logging
 	* WebTarget
 	* ProfileTarget
+- caching
+	* a console command to clear cached data
+
+---
+
 - base
 	* module
 	  - Module should be able to define its own configuration including routes. Application should be able to overwrite it.
@@ -16,17 +28,6 @@
 		* support for markdown syntax
 		* support for [[name]]
 		* consider to be released as a separate tool for user app docs
-- caching
-	* a way to invalidate/clear cached data
-	* a command to clear cached data
-- db
-	* pgsql, sql server, oracle, db2 drivers
-	  * write a guide on creating own schema definitions
-	* document-based (should allow storage-specific methods additionally to generic ones)
-	  * mongodb
-	* key-value-based (should allow storage-specific methods additionally to generic ones)
-	  * redis
-	  * memcachedb
 - i18n
 	* consider using PHP built-in support and data
 	* message translations, choice format