diff --git a/src/applications/cache/PhabricatorCaches.php b/src/applications/cache/PhabricatorCaches.php
index 5824c6458c..1127a7312b 100644
--- a/src/applications/cache/PhabricatorCaches.php
+++ b/src/applications/cache/PhabricatorCaches.php
@@ -206,40 +206,12 @@ final class PhabricatorCaches extends Phobject {
     // otherwise (we desire this property to give the cache the best hit rate
     // we can).
 
-    // In some setups, the parent PID is more stable and longer-lived that the
-    // PID (e.g., under apache, our PID will be a worker while the ppid will
-    // be the main httpd process). If we're confident we're running under such
-    // a setup, we can try to use the PPID as the basis for our cache instead
-    // of our own PID.
-    $use_ppid = false;
-
-    switch (php_sapi_name()) {
-      case 'cli-server':
-        // This is the PHP5.4+ built-in webserver. We should use the pid
-        // (the server), not the ppid (probably a shell or something).
-        $use_ppid = false;
-        break;
-      case 'fpm-fcgi':
-        // We should be safe to use PPID here.
-        $use_ppid = true;
-        break;
-      case 'apache2handler':
-        // We're definitely safe to use the PPID.
-        $use_ppid = true;
-        break;
-    }
+    // Unfortunately, we don't have a very good strategy for minimizing the
+    // churn rate of the cache. We previously tried to use the parent process
+    // PID in some cases, but this was not reliable. See T9599 for one case of
+    // this.
 
     $pid_basis = getmypid();
-    if ($use_ppid) {
-      if (function_exists('posix_getppid')) {
-        $parent_pid = posix_getppid();
-        // On most systems, normal processes can never have PIDs lower than 100,
-        // so something likely went wrong if we we get one of these.
-        if ($parent_pid > 100) {
-          $pid_basis = $parent_pid;
-        }
-      }
-    }
 
     // If possible, we also want to know when the process launched, so we can
     // drop the cache if a process restarts but gets the same PID an earlier
diff --git a/src/applications/cache/spec/PhabricatorDataCacheSpec.php b/src/applications/cache/spec/PhabricatorDataCacheSpec.php
index f5fe1c6277..eae5d75790 100644
--- a/src/applications/cache/spec/PhabricatorDataCacheSpec.php
+++ b/src/applications/cache/spec/PhabricatorDataCacheSpec.php
@@ -63,7 +63,9 @@ final class PhabricatorDataCacheSpec extends PhabricatorCacheSpec {
   private function initNoneSpec() {
     if (version_compare(phpversion(), '5.5', '>=')) {
       $message = pht(
-        'Installing the "APCu" PHP extension will improve performance.');
+        'Installing the "APCu" PHP extension will improve performance. '.
+        'This extension is strongly recommended. Without it, Phabricator '.
+        'must rely on a very inefficient disk-based cache.');
 
       $this
         ->newIssue('extension.apcu')