From 075c08fc57608ecfbabbe024fb65153f3bf871f7 Mon Sep 17 00:00:00 2001
From: Mark Johnson <mark.johnson@catalyst-eu.net>
Date: Fri, 19 Jul 2024 16:40:52 +0100
Subject: [PATCH] MDL-82545 gradereport_grader: Limit grades per page

This replaces the limit on the number of students per page with a number
of grades per page, to take into account the number of grade items on a
course.
---
 grade/report/grader/index.php | 11 ++++++++---
 grade/report/grader/lib.php   | 24 ++++++++++++++++++++++--
 2 files changed, 30 insertions(+), 5 deletions(-)

diff --git a/grade/report/grader/index.php b/grade/report/grader/index.php
index 307b9015e03..f780b84157a 100644
--- a/grade/report/grader/index.php
+++ b/grade/report/grader/index.php
@@ -28,6 +28,10 @@ require_once($CFG->dirroot.'/user/renderer.php');
 require_once($CFG->dirroot.'/grade/lib.php');
 require_once($CFG->dirroot.'/grade/report/grader/lib.php');
 
+// This report may require a lot of memory and time on large courses.
+raise_memory_limit(MEMORY_HUGE);
+set_time_limit(120);
+
 $courseid      = required_param('id', PARAM_INT);        // course id
 $page          = optional_param('page', 0, PARAM_INT);   // active page
 $edit          = optional_param('edit', -1, PARAM_BOOL); // sticky editting mode
@@ -192,8 +196,9 @@ if ($studentsperpage) {
 $pagingoptions = array_unique($pagingoptions);
 sort($pagingoptions);
 $pagingoptions = array_combine($pagingoptions, $pagingoptions);
-if ($numusers > grade_report_grader::MAX_STUDENTS_PER_PAGE) {
-    $pagingoptions['0'] = grade_report_grader::MAX_STUDENTS_PER_PAGE;
+$maxusers = $report->get_max_students_per_page();
+if ($numusers > $maxusers) {
+    $pagingoptions['0'] = $maxusers;
 } else {
     $pagingoptions['0'] = get_string('all');
 }
@@ -216,7 +221,7 @@ $footercontent = html_writer::div(
 );
 
 // The number of students per page is always limited even if it is claimed to be unlimited.
-$studentsperpage = $studentsperpage ?: grade_report_grader::MAX_STUDENTS_PER_PAGE;
+$studentsperpage = $studentsperpage ?: $maxusers;
 $footercontent .= html_writer::div(
     $OUTPUT->paging_bar($numusers, $report->page, $studentsperpage, $report->pbarurl),
     'col'
diff --git a/grade/report/grader/lib.php b/grade/report/grader/lib.php
index 5a6bdead030..717a05e2ffb 100644
--- a/grade/report/grader/lib.php
+++ b/grade/report/grader/lib.php
@@ -105,6 +105,13 @@ class grade_report_grader extends grade_report {
     /** @var int Maximum number of students that can be shown on one page */
     public const MAX_STUDENTS_PER_PAGE = 5000;
 
+    /**
+     * @var int The maximum number of grades that can be shown on one page.
+     *
+     * More than this causes issues for the browser due to the size of the page.
+     */
+    public const MAX_GRADES_PER_PAGE = 200000;
+
     /** @var int[] List of available options on the pagination dropdown */
     public const PAGINATION_OPTIONS = [20, 100];
 
@@ -466,9 +473,10 @@ class grade_report_grader extends grade_report {
                    $this->userwheresql
                    $this->groupwheresql
               ORDER BY $sort";
-        // We never work with unlimited result. Limit the number of records by MAX_STUDENTS_PER_PAGE if no other limit is specified.
+        // We never work with unlimited result. Limit the number of records by $this->get_max_students_per_page() if no other limit
+        // is specified.
         $studentsperpage = ($this->get_students_per_page() && !$allusers) ?
-            $this->get_students_per_page() : static::MAX_STUDENTS_PER_PAGE;
+            $this->get_students_per_page() : $this->get_max_students_per_page();
         $this->users = $DB->get_records_sql($sql, $params, $studentsperpage * $this->page, $studentsperpage);
 
         if (empty($this->users)) {
@@ -526,6 +534,18 @@ class grade_report_grader extends grade_report {
         return $this->allgradeitems;
     }
 
+    /**
+     * Return the maximum number of students we can display per page.
+     *
+     * This is based on the number of grade items on the course, to limit the overall number of grades displayed on a single page.
+     * Trying to display too many grades causes browser issues.
+     *
+     * @return int
+     */
+    public function get_max_students_per_page(): int {
+        return round(static::MAX_GRADES_PER_PAGE / count($this->get_allgradeitems()));
+    }
+
     /**
      * we supply the userids in this query, and get all the grades
      * pulls out all the grades, this does not need to worry about paging