From 4eba620ae3c8e2bcbbe3599c9db4dff43879ff27 Mon Sep 17 00:00:00 2001
From: Jun Pataleta <jun@moodle.com>
Date: Mon, 11 Apr 2016 10:10:00 +0800
Subject: [PATCH] MDL-53425 blocklib: Perform deletion of block instances by
 chunk

---
 lib/blocklib.php | 32 +++++++++++++++++++++-----------
 my/lib.php       | 24 ++++++++++++------------
 2 files changed, 33 insertions(+), 23 deletions(-)

diff --git a/lib/blocklib.php b/lib/blocklib.php
index 9a7c9963d52..23d99f5ec8a 100644
--- a/lib/blocklib.php
+++ b/lib/blocklib.php
@@ -2073,21 +2073,31 @@ function blocks_delete_instance($instance, $nolongerused = false, $skipblockstab
 function blocks_delete_instances($instanceids) {
     global $DB;
 
-    $instances = $DB->get_recordset_list('block_instances', 'id', $instanceids);
-    foreach ($instances as $instance) {
-        blocks_delete_instance($instance, false, true);
+    $limit = 1000;
+    $count = count($instanceids);
+    $chunks = [$instanceids];
+    if ($count > $limit) {
+        $chunks = array_chunk($instanceids, $limit);
     }
-    $instances->close();
 
-    $DB->delete_records_list('block_positions', 'blockinstanceid', $instanceids);
-    $DB->delete_records_list('block_instances', 'id', $instanceids);
+    // Perform deletion for each chunk.
+    foreach ($chunks as $chunk) {
+        $instances = $DB->get_recordset_list('block_instances', 'id', $chunk);
+        foreach ($instances as $instance) {
+            blocks_delete_instance($instance, false, true);
+        }
+        $instances->close();
 
-    $preferences = array();
-    foreach ($instanceids as $instanceid) {
-        $preferences[] = 'block' . $instanceid . 'hidden';
-        $preferences[] = 'docked_block_instance_' . $instanceid;
+        $DB->delete_records_list('block_positions', 'blockinstanceid', $chunk);
+        $DB->delete_records_list('block_instances', 'id', $chunk);
+
+        $preferences = array();
+        foreach ($chunk as $instanceid) {
+            $preferences[] = 'block' . $instanceid . 'hidden';
+            $preferences[] = 'docked_block_instance_' . $instanceid;
+        }
+        $DB->delete_records_list('user_preferences', 'name', $preferences);
     }
-    $DB->delete_records_list('user_preferences', 'name', $preferences);
 }
 
 /**
diff --git a/my/lib.php b/my/lib.php
index bd3219d440f..e0a4d37dd3b 100644
--- a/my/lib.php
+++ b/my/lib.php
@@ -150,22 +150,23 @@ function my_reset_page_for_all_users($private = MY_PAGE_PRIVATE, $pagetype = 'my
     $where = 'userid IS NOT NULL AND private = :private';
     $params = array('private' => $private);
     $pages = $DB->get_recordset_select('my_pages', $where, $params, 'id, userid');
-    $pageids = array();
     $blockids = array();
 
     foreach ($pages as $page) {
-        $pageids[] = $page->id;
         $usercontext = context_user::instance($page->userid);
 
         // Find all block instances in that page.
-        $blocks = $DB->get_recordset('block_instances', array('parentcontextid' => $usercontext->id,
-            'pagetypepattern' => $pagetype), '', 'id, subpagepattern');
-        foreach ($blocks as $block) {
-            if (is_null($block->subpagepattern) || $block->subpagepattern == $page->id) {
-                $blockids[] = $block->id;
-            }
+        $blockswhere = 'parentcontextid = :parentcontextid AND
+            pagetypepattern = :pagetypepattern AND
+            (subpagepattern IS NULL OR subpagepattern = :subpagepattern)';
+        $blockswhereparams = [
+            'parentcontextid' => $usercontext->id,
+            'pagetypepattern' => $pagetype,
+            'subpagepattern' => $page->id
+        ];
+        if ($pageblockids = $DB->get_fieldset_select('block_instances', 'id', $blockswhere, $blockswhereparams)) {
+            $blockids = array_merge($blockids, $pageblockids);
         }
-        $blocks->close();
     }
     $pages->close();
 
@@ -178,9 +179,8 @@ function my_reset_page_for_all_users($private = MY_PAGE_PRIVATE, $pagetype = 'my
     }
 
     // Finally delete the pages.
-    if (!empty($pageids)) {
-        list($insql, $inparams) = $DB->get_in_or_equal($pageids);
-        $DB->delete_records_select('my_pages', "id $insql", $pageids);
+    if (!empty($pages)) {
+        $DB->delete_records_select('my_pages', $where, $params);
     }
 
     // We should be good to go now.