diff --git a/src/applications/cache/PhabricatorCaches.php b/src/applications/cache/PhabricatorCaches.php
--- a/src/applications/cache/PhabricatorCaches.php
+++ b/src/applications/cache/PhabricatorCaches.php
@@ -143,6 +143,39 @@
   }
 
 
+/* -(  Server State Cache  )------------------------------------------------- */
+
+
+  /**
+   * Highly specialized cache for storing server process state.
+   *
+   * We use this cache to track initial steps in the setup phase, before
+   * configuration is loaded.
+   *
+   * This cache does NOT use the cache namespace (it must be accessed before
+   * we build configuration), and is global across all instances on the host.
+   *
+   * @return PhutilKeyValueCacheStack Best available server state cache stack.
+   * @task setup
+   */
+  public static function getServerStateCache() {
+    static $cache;
+    if (!$cache) {
+      $caches = self::buildSetupCaches('phabricator-server');
+
+      // NOTE: We are NOT adding a cache namespace here! This cache is shared
+      // across all instances on the host.
+
+      $caches = self::addProfilerToCaches($caches);
+      $cache = id(new PhutilKeyValueCacheStack())
+        ->setCaches($caches);
+
+    }
+    return $cache;
+  }
+
+
+
 /* -(  Setup Cache  )-------------------------------------------------------- */
 
 
@@ -163,7 +196,7 @@
   public static function getSetupCache() {
     static $cache;
     if (!$cache) {
-      $caches = self::buildSetupCaches();
+      $caches = self::buildSetupCaches('phabricator-setup');
       $cache = self::newStackFromCaches($caches);
     }
     return $cache;
@@ -173,7 +206,7 @@
   /**
    * @task setup
    */
-  private static function buildSetupCaches() {
+  private static function buildSetupCaches($cache_name) {
     // If this is the CLI, just build a setup cache.
     if (php_sapi_name() == 'cli') {
       return array();
@@ -188,7 +221,7 @@
 
     // If we don't have APC, build a poor approximation on disk. This is still
     // much better than nothing; some setup steps are quite slow.
-    $disk_path = self::getSetupCacheDiskCachePath();
+    $disk_path = self::getSetupCacheDiskCachePath($cache_name);
     if ($disk_path) {
       $disk = new PhutilOnDiskKeyValueCache();
       $disk->setCacheFile($disk_path);
@@ -205,7 +238,7 @@
   /**
    * @task setup
    */
-  private static function getSetupCacheDiskCachePath() {
+  private static function getSetupCacheDiskCachePath($name) {
     // The difficulty here is in choosing a path which will change on server
     // restart (we MUST have this property), but as rarely as possible
     // otherwise (we desire this property to give the cache the best hit rate
@@ -230,7 +263,7 @@
 
     $tmp_dir = sys_get_temp_dir();
 
-    $tmp_path = $tmp_dir.DIRECTORY_SEPARATOR.'phabricator-setup';
+    $tmp_path = $tmp_dir.DIRECTORY_SEPARATOR.$name;
     if (!file_exists($tmp_path)) {
       @mkdir($tmp_path);
     }
diff --git a/src/applications/config/check/PhabricatorSetupCheck.php b/src/applications/config/check/PhabricatorSetupCheck.php
--- a/src/applications/config/check/PhabricatorSetupCheck.php
+++ b/src/applications/config/check/PhabricatorSetupCheck.php
@@ -74,6 +74,9 @@
     $cache = PhabricatorCaches::getSetupCache();
     $cache->setKey('phabricator.setup.issue-keys', $keys);
 
+    $server_cache = PhabricatorCaches::getServerStateCache();
+    $server_cache->setKey('phabricator.in-flight', 1);
+
     if ($update_database) {
       $db_cache = new PhabricatorKeyValueDatabaseCache();
       try {
@@ -204,7 +207,8 @@
    * @return bool True if we've made it through setup since the last restart.
    */
   final public static function isInFlight() {
-    return (self::getOpenSetupIssueKeys() !== null);
+    $cache = PhabricatorCaches::getServerStateCache();
+    return (bool)$cache->getKey('phabricator.in-flight');
   }
 
   final public static function loadAllChecks() {
diff --git a/src/infrastructure/env/PhabricatorEnv.php b/src/infrastructure/env/PhabricatorEnv.php
--- a/src/infrastructure/env/PhabricatorEnv.php
+++ b/src/infrastructure/env/PhabricatorEnv.php
@@ -315,14 +315,6 @@
    * @task read
    */
   public static function getEnvConfig($key) {
-    if (isset(self::$cache[$key])) {
-      return self::$cache[$key];
-    }
-
-    if (array_key_exists($key, self::$cache)) {
-      return self::$cache[$key];
-    }
-
     if (!self::$sourceStack) {
       throw new Exception(
         pht(
@@ -331,6 +323,14 @@
           $key));
     }
 
+    if (isset(self::$cache[$key])) {
+      return self::$cache[$key];
+    }
+
+    if (array_key_exists($key, self::$cache)) {
+      return self::$cache[$key];
+    }
+
     $result = self::$sourceStack->getKeys(array($key));
     if (array_key_exists($key, $result)) {
       self::$cache[$key] = $result[$key];