Issue #1930960 by pounard, iamEAP, pjcdawkins, msonnabaum, David_Rothstein: Fixed Block caching disable hardcoded on sites with hook_node_grant() causes serious performance troubles when not necessary.

Author: DavidRothstein

CHANGELOG.txt

@@ -1,6 +1,8 @@
 
 Drupal 7.33, xxxx-xx-xx (development version)
 -----------------------
+- Added a "block_cache_bypass_node_grants" variable to allow sites which have
+  node access modules enabled to use the block cache if desired (API addition).
 - Made image derivative generation HTTP requests return a 404 error (rather
   than a 500 error) when the source image does not exist.
 - Fixed a bug which caused user pictures to be removed from the user object

modules/block/block.module

@@ -848,10 +848,19 @@ function block_block_list_alter(&$blocks) {
  *   An array of visible blocks as expected by drupal_render().
  */
 function _block_render_blocks($region_blocks) {
-  // Block caching is not compatible with node access modules. We also
-  // preserve the submission of forms in blocks, by fetching from cache only
+  $cacheable = TRUE;
+
+  // We preserve the submission of forms in blocks, by fetching from cache only
   // if the request method is 'GET' (or 'HEAD').
-  $cacheable = !count(module_implements('node_grants')) && ($_SERVER['REQUEST_METHOD'] == 'GET' || $_SERVER['REQUEST_METHOD'] == 'HEAD');
+  if ($_SERVER['REQUEST_METHOD'] != 'GET' && $_SERVER['REQUEST_METHOD'] != 'HEAD') {
+    $cacheable = FALSE;
+  }
+  // Block caching is not usually compatible with node access modules, so by
+  // default it is disabled when node access modules exist. However, it can be
+  // allowed by using the variable 'block_cache_bypass_node_grants'.
+  elseif (!variable_get('block_cache_bypass_node_grants', FALSE) && count(module_implements('node_grants'))) {
+    $cacheable = FALSE;
+  }
 
   // Proceed to loop over all blocks in order to compute their respective cache
   // identifiers; this allows us to do one single cache_get_multiple() call
@@ -1054,7 +1063,7 @@ function block_menu_delete($menu) {
  * Implements hook_form_FORM_ID_alter().
  */
 function block_form_system_performance_settings_alter(&$form, &$form_state) {
-  $disabled = count(module_implements('node_grants'));
+  $disabled = (!variable_get('block_cache_bypass_node_grants', FALSE) && count(module_implements('node_grants')));
   $form['caching']['block_cache'] = array(
     '#type' => 'checkbox',
     '#title' => t('Cache blocks'),

sites/default/default.settings.php

@@ -434,6 +434,18 @@
 # $conf['css_gzip_compression'] = FALSE;
 # $conf['js_gzip_compression'] = FALSE;
 
+/**
+ * Block caching:
+ *
+ * Block caching may not be compatible with node access modules depending on
+ * how the original block cache policy is defined by the module that provides
+ * the block. By default, Drupal therefore disables block caching when one or
+ * more modules implement hook_node_grants(). If you consider block caching to
+ * be safe on your site and want to bypass this restriction, uncomment the line
+ * below.
+ */
+# $conf['block_cache_bypass_node_grants'] = TRUE;
+
 /**
  * String overrides:
  *