diff --git a/includes/bootstrap.inc b/includes/bootstrap.inc
index de9a175..091d7e7 100644
--- a/includes/bootstrap.inc
+++ b/includes/bootstrap.inc
@@ -729,31 +729,19 @@ function drupal_get_filename($type, $name, $filename = NULL) {
  * file.
  */
 function variable_initialize($conf = array()) {
-  // NOTE: caching the variables improves performance by 20% when serving
-  // cached pages.
-  if ($cached = cache_get('variables', 'cache_bootstrap')) {
+  $cache = &drupal_static('variable', array());
+  if ($cached = cache_get('variable_cache', 'cache_bootstrap')) {
     $variables = $cached->data;
   }
   else {
-    // Cache miss. Avoid a stampede.
-    $name = 'variable_init';
-    if (!lock_acquire($name, 1)) {
-      // Another request is building the variable cache.
-      // Wait, then re-run this function.
-      lock_wait($name);
-      return variable_initialize($conf);
-    }
-    else {
-      // Proceed with variable rebuild.
-      $variables = array_map('unserialize', db_query('SELECT name, value FROM {variable}')->fetchAllKeyed());
-      cache_set('variables', $variables, 'cache_bootstrap');
-      lock_release($name);
-    }
+    $variables = array();
   }
-
   foreach ($conf as $name => $value) {
     $variables[$name] = $value;
   }
+  // Set $cache['#initialized']. After variable_initialize(), variable_set()
+  // queries the database if variables aren't already in $conf.
+  $cache['#initialized'] = TRUE;
 
   return $variables;
 }
@@ -778,6 +766,25 @@ function variable_initialize($conf = array()) {
  */
 function variable_get($name, $default = NULL) {
   global $conf;
+  if (isset($conf[$name])) {
+    return $conf[$name];
+  }
+  // Use the advanced drupal_static() pattern, since this is called very often.
+  static $drupal_static_fast;
+  if (!isset($drupal_static_fast)) {
+    $drupal_static_fast['cache'] = &drupal_static('variable', array());
+  }
+  $cache = &$drupal_static_fast['cache'];
+
+  // $cache is populated in variable_initialize() for each request. If it's not
+  // available here we are in a lower bootstrap phase where the database and
+  // cache system may not be available yet.
+  if (!empty($cache['#initialized']) && !array_key_exists($name,  $conf)) {
+    // If the variable is not already cached, look it up from the database.
+    $result = db_query('SELECT value FROM {variable} WHERE name = :name', array(':name' => $name))->fetchField();
+    $value = $result ? unserialize($result) : $default;
+    $conf[$name] = $cache[$name] = $value;
+  }
 
   return isset($conf[$name]) ? $conf[$name] : $default;
 }
@@ -799,13 +806,10 @@ function variable_get($name, $default = NULL) {
  * @see variable_get()
  */
 function variable_set($name, $value) {
-  global $conf;
-
   db_merge('variable')->key(array('name' => $name))->fields(array('value' => serialize($value)))->execute();
-
-  cache_clear_all('variables', 'cache_bootstrap');
-
-  $conf[$name] = $value;
+  $GLOBALS['conf'][$name] = $value;
+  variable_write_cache('variable_cache', 'cache_bootstrap', array('name' => $name, 'value' => $value));
+  variable_reset_cache(FALSE);
 }
 
 /**
@@ -822,14 +826,82 @@ function variable_set($name, $value) {
  * @see variable_set()
  */
 function variable_del($name) {
-  global $conf;
-
   db_delete('variable')
     ->condition('name', $name)
     ->execute();
-  cache_clear_all('variables', 'cache_bootstrap');
+  variable_write_cache('variable_cache', 'cache_bootstrap', array('name' => $name, 'unset' => TRUE));
 
-  unset($conf[$name]);
+  unset($GLOBALS['conf'][$name]);
+  variable_reset_cache(FALSE);
+}
+
+/**
+ * Reset the variable cache.
+ *
+ * @param $bootstrap
+ *   Optional parameter to reset the variable cache for bootstrap. If a
+ *   variable is not cached for bootstrap, there is no need to clear the cache.
+ *   Defaults to TRUE.
+ */
+function variable_reset_cache($bootstrap = TRUE) {
+  if ($bootstrap) {
+    cache_clear_all('variable_cache', 'cache_bootstrap');
+  }
+  cache_clear_all('variable_cache:', 'cache', TRUE);
+  $cache = &drupal_static('variable');
+  $cache = array('#initialized' => TRUE);
+}
+
+/**
+ * Update the variable cache after a cache miss, variable_set() or variable_del().
+ *
+ * Since the bootstrap variables cache may have high contention, to avoid
+ * stampedes we updated the cached variables and refresh the entry after
+ * variable_set() and variable_del() instead of just clearing the cache.
+ * This means that subsequent requests will get a new copy of the cache instead
+ * of having to rebuild it from scratch.
+ *
+ * @param $cid
+ *   The cache ID.
+ * @param $bin
+ *   The cache bin.
+ * @param $options
+ *   Optional paramater to allow updating the cache for a specific variable.
+ *   This is an array in the form of array('name' => $name, 'value' => $value)
+ *   or array('name' => $name, 'unset' => TRUE).
+ */
+function variable_write_cache($cid, $bin, $options = array()) {
+  $cache = &drupal_static('variable', array());
+  $write = FALSE;
+  // Clear out the #initialized flag.
+  unset($cache['#initialized']);
+  if (!empty($cache)) {
+    $write = TRUE;
+  }
+  if ($write || $options) {
+    // Get a fresh copy of the variable cache from cache_get(), this will
+    // include any changes made by other requests between variable_initialize()
+    // and variable_write_cache().
+    if ($cached = cache_get($cid, $bin)) {
+      $current_cache = $cached->data;
+      $cache = array_merge($current_cache, $cache);
+      if ($options) {
+        // Use array_key_exists() here because NULL is a valid value.
+        if (!empty($options['unset']) && array_key_exists($options['name'], $cache)) {
+          $write = TRUE;
+          unset($cache[$options['name']]);
+        }
+        elseif (array_key_exists('value', $options) && array_key_exists($options['name'], $cache)) {
+          $write = TRUE;
+          $cache[$options['name']] = $options['value'];
+        }
+      }
+    }
+    if ($write) {
+      cache_set($cid, $cache, $bin);
+    }
+  }
+  $cache = array('#initialized' => TRUE);
 }
 
 /**
@@ -2057,6 +2129,8 @@ function _drupal_bootstrap_page_cache() {
       if (variable_get('page_cache_invoke_hooks', TRUE)) {
         bootstrap_invoke_all('exit');
       }
+      // Allow the variables requested for cached pages to be cached.
+      variable_write_cache('variable_cache', 'cache_bootstrap');
       // We are done.
       exit;
     }
@@ -2124,10 +2198,6 @@ function _drupal_bootstrap_database() {
 function _drupal_bootstrap_variables() {
   global $conf;
 
-  // Initialize the lock system.
-  require_once DRUPAL_ROOT . '/' . variable_get('lock_inc', 'includes/lock.inc');
-  lock_initialize();
-
   // Load variables from the database, but do not overwrite variables set in settings.php.
   $conf = variable_initialize(isset($conf) ? $conf : array());
   // Load bootstrap modules.
@@ -2141,6 +2211,10 @@ function _drupal_bootstrap_variables() {
 function _drupal_bootstrap_page_header() {
   bootstrap_invoke_all('boot');
 
+  // Prepare for non-cached page workflow.
+  require_once DRUPAL_ROOT . '/' . variable_get('lock_inc', 'includes/lock.inc');
+  lock_initialize();
+
   if (!drupal_is_cli()) {
     ob_start();
     drupal_page_header();
diff --git a/includes/common.inc b/includes/common.inc
index 00b2e71..96b9e0d 100644
--- a/includes/common.inc
+++ b/includes/common.inc
@@ -2565,6 +2565,7 @@ function drupal_page_footer() {
   drupal_cache_system_paths();
   module_implements_write_cache();
   system_run_automated_cron();
+  variable_write_cache('variable_cache:' . arg(0), 'cache');
 }
 
 /**
@@ -2590,6 +2591,37 @@ function drupal_exit($destination = NULL) {
 }
 
 /**
+ * Initialize the variables cache after full bootstrap.
+ */
+function variable_initialize_full() {
+  // Allow variables fetched up to this point to be cached in the global
+  // variable_bootstrap cache.
+  // The cache system often relies on the variable system, so ensure that
+  // any variables needed for the cache_get() call are requested before we
+  // actually set the cache.
+  // After full bootstrap, we segment the variables cache by system path root.
+  // For example 'node' or 'admin'.
+  $cached = cache_get('variable_cache:' . arg(0), 'cache');
+  variable_write_cache('variable_cache', 'cache_bootstrap');
+  // For example 'node' or 'admin'.
+
+  $cache = &drupal_static('variable', array());
+  if ($cached) {
+    $variables = $cached->data;
+  }
+  else {
+    $variables = array();
+  }
+
+  // Ensure existing variables in $conf override cached values.
+  foreach ($GLOBALS['conf'] as $name => $value) {
+    $variables[$name] = $value;
+  }
+  $cache['#initialized'] = TRUE;
+  $GLOBALS['conf'] = $variables;
+}
+
+/**
  * Form an associative array from a linear array.
  *
  * This function walks through the provided array and constructs an associative
@@ -4929,6 +4961,7 @@ function _drupal_bootstrap_full() {
     menu_set_custom_theme();
     drupal_theme_initialize();
     module_invoke_all('init');
+    variable_initialize_full();
   }
 }
 
diff --git a/modules/color/color.module b/modules/color/color.module
index ff6c70e..aa13b45 100644
--- a/modules/color/color.module
+++ b/modules/color/color.module
@@ -159,7 +159,7 @@ function color_scheme_form($complete_form, &$form_state, $theme) {
 
   // See if we're using a predefined scheme.
   // Note: we use the original theme when the default scheme is chosen.
-  $current_scheme = variable_get('color_' . $theme . '_palette', array());
+  $current_scheme = variable_get('color_' . $theme . '_palette');
   foreach ($schemes as $key => $scheme) {
     if ($current_scheme == $scheme) {
       $scheme_name = $key;
diff --git a/modules/simpletest/drupal_web_test_case.php b/modules/simpletest/drupal_web_test_case.php
index a0cd114..b6de0e8 100644
--- a/modules/simpletest/drupal_web_test_case.php
+++ b/modules/simpletest/drupal_web_test_case.php
@@ -1238,16 +1238,6 @@ class DrupalWebTestCase extends DrupalTestCase {
       ->condition('test_id', $this->testId)
       ->execute();
 
-    // Clone the current connection and replace the current prefix.
-    $connection_info = Database::getConnectionInfo('default');
-    Database::renameConnection('default', 'simpletest_original_default');
-    foreach ($connection_info as $target => $value) {
-      $connection_info[$target]['prefix'] = array(
-        'default' => $value['prefix']['default'] . $this->databasePrefix,
-      );
-    }
-    Database::addConnectionInfo('default', 'default', $connection_info['default']);
-
     // Store necessary current values before switching to prefixed database.
     $this->originalLanguage = $language;
     $this->originalLanguageDefault = variable_get('language_default');
@@ -1276,6 +1266,16 @@ class DrupalWebTestCase extends DrupalTestCase {
     file_prepare_directory($temp_files_directory, FILE_CREATE_DIRECTORY);
     $this->generatedTestFiles = FALSE;
 
+    // Clone the current connection and replace the current prefix.
+    $connection_info = Database::getConnectionInfo('default');
+    Database::renameConnection('default', 'simpletest_original_default');
+    foreach ($connection_info as $target => $value) {
+      $connection_info[$target]['prefix'] = array(
+        'default' => $value['prefix']['default'] . $this->databasePrefix,
+      );
+    }
+    Database::addConnectionInfo('default', 'default', $connection_info['default']);
+
     // Log fatal errors.
     ini_set('log_errors', 1);
     ini_set('error_log', $public_files_directory . '/error.log');
@@ -1429,7 +1429,7 @@ class DrupalWebTestCase extends DrupalTestCase {
    */
   protected function refreshVariables() {
     global $conf;
-    cache_clear_all('variables', 'cache_bootstrap');
+    variable_reset_cache();
     $conf = variable_initialize();
   }
 
diff --git a/modules/simpletest/tests/file.test b/modules/simpletest/tests/file.test
index dc12b1b..0794722 100644
--- a/modules/simpletest/tests/file.test
+++ b/modules/simpletest/tests/file.test
@@ -2241,6 +2241,7 @@ class FileDownloadTest extends FileTestCase {
 
     // Deny access to all downloads via a -1 header.
     file_test_set_return('download', -1);
+    variable_reset_cache();
     $this->drupalHead($url);
     $this->assertResponse(403, t('Correctly denied access to a file when file_test sets the header to -1.'));
 
diff --git a/modules/simpletest/tests/upgrade/upgrade.test b/modules/simpletest/tests/upgrade/upgrade.test
index 1ef8525..f118df9 100644
--- a/modules/simpletest/tests/upgrade/upgrade.test
+++ b/modules/simpletest/tests/upgrade/upgrade.test
@@ -33,6 +33,26 @@ abstract class UpgradePathTestCase extends DrupalWebTestCase {
   protected function setUp() {
     global $user, $language, $conf;
 
+    // Store necessary current values before switching to prefixed database.
+    $this->originalLanguage = $language;
+    $this->originalLanguageDefault = variable_get('language_default');
+    $this->originalFileDirectory = variable_get('file_public_path', conf_path() . '/files');
+    $this->originalProfile = drupal_get_profile();
+    $clean_url_original = variable_get('clean_url', 0);
+
+    // Create test directories ahead of installation so fatal errors and debug
+    // information can be logged during installation process.
+    // Use mock files directories with the same prefix as the database.
+    $public_files_directory  = $this->originalFileDirectory . '/simpletest/' . substr($this->databasePrefix, 10);
+    $private_files_directory = $public_files_directory . '/private';
+    $temp_files_directory    = $private_files_directory . '/temp';
+
+    // Create the directories.
+    file_prepare_directory($public_files_directory, FILE_CREATE_DIRECTORY | FILE_MODIFY_PERMISSIONS);
+    file_prepare_directory($private_files_directory, FILE_CREATE_DIRECTORY);
+    file_prepare_directory($temp_files_directory, FILE_CREATE_DIRECTORY);
+    $this->generatedTestFiles = FALSE;
+
     // Load the Update API.
     require_once DRUPAL_ROOT . '/includes/update.inc';
 
@@ -59,31 +79,11 @@ abstract class UpgradePathTestCase extends DrupalWebTestCase {
     }
     Database::addConnectionInfo('default', 'default', $connection_info['default']);
 
-    // Store necessary current values before switching to prefixed database.
-    $this->originalLanguage = $language;
-    $this->originalLanguageDefault = variable_get('language_default');
-    $this->originalFileDirectory = variable_get('file_public_path', conf_path() . '/files');
-    $this->originalProfile = drupal_get_profile();
-    $clean_url_original = variable_get('clean_url', 0);
-
     // Unregister the registry.
     // This is required to make sure that the database layer works properly.
     spl_autoload_unregister('drupal_autoload_class');
     spl_autoload_unregister('drupal_autoload_interface');
 
-    // Create test directories ahead of installation so fatal errors and debug
-    // information can be logged during installation process.
-    // Use mock files directories with the same prefix as the database.
-    $public_files_directory  = $this->originalFileDirectory . '/simpletest/' . substr($this->databasePrefix, 10);
-    $private_files_directory = $public_files_directory . '/private';
-    $temp_files_directory    = $private_files_directory . '/temp';
-
-    // Create the directories.
-    file_prepare_directory($public_files_directory, FILE_CREATE_DIRECTORY | FILE_MODIFY_PERMISSIONS);
-    file_prepare_directory($private_files_directory, FILE_CREATE_DIRECTORY);
-    file_prepare_directory($temp_files_directory, FILE_CREATE_DIRECTORY);
-    $this->generatedTestFiles = FALSE;
-
     // Log fatal errors.
     ini_set('log_errors', 1);
     ini_set('error_log', $public_files_directory . '/error.log');
diff --git a/modules/system/system.test b/modules/system/system.test
index ae69d1f..a1a49c7 100644
--- a/modules/system/system.test
+++ b/modules/system/system.test
@@ -616,6 +616,7 @@ class CronRunTestCase extends DrupalWebTestCase {
     // Test if cron runs when the cron threshold was passed.
     $cron_last = time() - 200;
     variable_set('cron_last', $cron_last);
+    variable_reset_cache();
     $this->drupalGet('');
     sleep(1);
     $this->assertTrue($cron_last < variable_get('cron_last', NULL), t('Cron runs when the cron threshold is passed.'));