diff --git a/availability/condition/completion/tests/behat/availability_completion.feature b/availability/condition/completion/tests/behat/availability_completion.feature
index 0f4c121d968..67743d3f1c0 100644
--- a/availability/condition/completion/tests/behat/availability_completion.feature
+++ b/availability/condition/completion/tests/behat/availability_completion.feature
@@ -54,3 +54,64 @@ Feature: availability_completion
     # Mark page 1 complete
     When I toggle the manual completion state of "Page 1"
     Then I should see "Page 2" in the "region-main" "region"
+
+  @javascript
+  Scenario: test completion and course cache rebuild
+    Given the following "activities" exist:
+      | activity | name    | intro   | course | idnumber |
+      | forum    | forum 1 | forum 1 | C1     | forum1   |
+    And I log in as "teacher1"
+    And I am on "Course 1" course homepage with editing mode on
+    And I open "forum 1" actions menu
+    And I click on "Edit settings" "link" in the "forum 1" activity
+    And I set the following fields to these values:
+      | Completion tracking    | Show activity as complete when conditions are met |
+      | completionview         | 1                                                 |
+      | completionpostsenabled | 1                                                 |
+      | completionposts        | 2                                                 |
+    And I press "Save and return to course"
+
+    And I add a new discussion to "forum 1" forum with:
+      | Subject | Forum post 1 |
+      | Message | This is the body |
+
+    And I am on "Course 1" course homepage with editing mode on
+    And I add a "Page" to section "2"
+    And I set the following fields to these values:
+      | Name         | Page 2 |
+      | Description  | Test   |
+      | Page content | Test   |
+    And I expand all fieldsets
+    And I press "Add restriction..."
+    And I click on "Activity completion" "button" in the "Add restriction..." "dialogue"
+    And I click on ".availability-item .availability-eye img" "css_element"
+    And I set the following fields to these values:
+      | Required completion status | must be marked complete |
+      | cm                         | forum 1                 |
+    And I press "Save and return to course"
+
+    When I log out
+    And I log in as "student1"
+    And I am on "Course 1" course homepage
+
+    # Page 2 should not appear yet.
+    Then I should not see "Page 2" in the "region-main" "region"
+    And I click on "forum 1" "link" in the "region-main" "region"
+    # Page 2 should not appear yet.
+    Then I should not see "Page 2" in the "region-main" "region"
+
+    When I log out
+    And I log in as "teacher1"
+    And I am on "Course 1" course homepage
+    And I am on the "forum 1" "forum activity editing" page
+    And I expand all fieldsets
+    And I set the following fields to these values:
+      | completionpostsenabled | 0 |
+    And I press "Save and display"
+
+    When I log out
+    And I log in as "student1"
+    And I am on "Course 1" course homepage
+    And I click on "forum 1" "link" in the "region-main" "region"
+    And I am on "Course 1" course homepage
+    Then I should see "Page 2" in the "region-main" "region"
diff --git a/availability/condition/date/classes/condition.php b/availability/condition/date/classes/condition.php
index 63b61b4ebce..fdf2f705006 100644
--- a/availability/condition/date/classes/condition.php
+++ b/availability/condition/date/classes/condition.php
@@ -292,14 +292,15 @@ class condition extends \core_availability\condition {
                 $updatesection->availability = json_encode($tree->save());
                 $updatesection->timemodified = time();
                 $DB->update_record('course_sections', $updatesection);
+                course_purge_section_cache($section);
 
                 $anychanged = true;
             }
         }
 
-        // Ensure course cache is cleared if required.
         if ($anychanged) {
-            rebuild_course_cache($courseid, true);
+            // Partial rebuild the sections which have been invalidated.
+            rebuild_course_cache($courseid, true, true);
         }
     }
 }
diff --git a/course/dnduploadlib.php b/course/dnduploadlib.php
index cf23b5da001..00216dc4441 100644
--- a/course/dnduploadlib.php
+++ b/course/dnduploadlib.php
@@ -614,8 +614,10 @@ class dndupload_ajax_processor {
         $visible = get_fast_modinfo($this->course)->get_section_info($this->section)->visible;
 
         $DB->set_field('course_modules', 'instance', $instanceid, array('id' => $this->cm->id));
+
+        course_purge_module_cache($this->cm);
         // Rebuild the course cache after update action
-        rebuild_course_cache($this->course->id, true);
+        rebuild_course_cache($this->course->id, true, true);
 
         $sectionid = course_add_cm_to_section($this->course, $this->cm->id, $this->section);
 
diff --git a/course/format/classes/base.php b/course/format/classes/base.php
index 23bb9b2d11e..1cfc6279eeb 100644
--- a/course/format/classes/base.php
+++ b/course/format/classes/base.php
@@ -1009,7 +1009,15 @@ abstract class base {
             }
         }
         if ($needrebuild) {
-            rebuild_course_cache($this->courseid, true);
+            if ($sectionid) {
+                $sectionrecord = $DB->get_record('course_sections', ['id' => $sectionid], 'course, section', MUST_EXIST);
+                course_purge_section_cache($sectionrecord);
+                // Partial rebuild sections that have been invalidated.
+                rebuild_course_cache($this->courseid, true, true);
+            } else {
+                // Full rebuild if sectionid is null.
+                rebuild_course_cache($this->courseid);
+            }
         }
         if ($changed) {
             // Reset internal caches.
@@ -1277,7 +1285,7 @@ abstract class base {
         }
         if (!is_object($section)) {
             $section = $DB->get_record('course_sections', array('course' => $this->get_courseid(), 'section' => $section),
-                'id,section,sequence,summary');
+                'id,course,section,sequence,summary');
         }
         if (!$section || !$section->section) {
             // Not possible to delete 0-section.
@@ -1314,7 +1322,9 @@ abstract class base {
         // Delete section and it's format options.
         $DB->delete_records('course_format_options', array('sectionid' => $section->id));
         $DB->delete_records('course_sections', array('id' => $section->id));
-        rebuild_course_cache($course->id, true);
+        course_purge_section_cache($section);
+        // Partial rebuild section cache that has been purged.
+        rebuild_course_cache($course->id, true, true);
 
         // Delete section summary files.
         $context = \context_course::instance($course->id);
diff --git a/course/lib.php b/course/lib.php
index 43733242a18..03d454fe95d 100644
--- a/course/lib.php
+++ b/course/lib.php
@@ -389,8 +389,12 @@ function course_integrity_check($courseid, $rawmods = null, $sections = null, $f
 /**
  * For a given course, returns an array of course activity objects
  * Each item in the array contains he following properties:
+ *
+ * @param int $courseid course id
+ * @param bool $usecache get activities from cache if modinfo exists when $usecache is true
+ * @return array list of activities
  */
-function get_array_of_activities($courseid) {
+function get_array_of_activities(int $courseid, bool $usecache = false): array {
 //  cm - course module id
 //  mod - name of the module (eg forum)
 //  section - the number of the section (eg week or topic)
@@ -406,12 +410,21 @@ function get_array_of_activities($courseid) {
         throw new moodle_exception('courseidnotfound');
     }
 
-    $mod = array();
-
     $rawmods = get_course_mods($courseid);
     if (empty($rawmods)) {
-        return $mod; // always return array
+        return [];
     }
+
+    $mods = [];
+    if ($usecache) {
+        // Get existing cache.
+        $cachecoursemodinfo = cache::make('core', 'coursemodinfo');
+        $coursemodinfo = $cachecoursemodinfo->get($courseid);
+        if ($coursemodinfo !== false) {
+            $mods = $coursemodinfo->modinfo;
+        }
+    }
+
     $courseformat = course_get_format($course);
 
     if ($sections = $DB->get_records('course_sections', array('course' => $courseid),
@@ -423,140 +436,152 @@ function get_array_of_activities($courseid) {
             $sections = $DB->get_records('course_sections', array('course' => $courseid),
                 'section ASC', 'id,section,sequence,visible');
         }
-        // Build array of activities.
-       foreach ($sections as $section) {
-           if (!empty($section->sequence)) {
-               $sequence = explode(",", $section->sequence);
-               foreach ($sequence as $seq) {
-                   if (empty($rawmods[$seq])) {
-                       continue;
-                   }
-                   // Adjust visibleoncoursepage, value in DB may not respect format availability.
-                   $rawmods[$seq]->visibleoncoursepage = (!$rawmods[$seq]->visible
-                           || $rawmods[$seq]->visibleoncoursepage
-                           || empty($CFG->allowstealth)
-                           || !$courseformat->allow_stealth_module_visibility($rawmods[$seq], $section)) ? 1 : 0;
 
-                   // Create an object that will be cached.
-                   $mod[$seq] = new stdClass();
-                   $mod[$seq]->id               = $rawmods[$seq]->instance;
-                   $mod[$seq]->cm               = $rawmods[$seq]->id;
-                   $mod[$seq]->mod              = $rawmods[$seq]->modname;
+        // Build array of activities.
+        foreach ($sections as $section) {
+            if (!empty($section->sequence)) {
+                $cmids = explode(",", $section->sequence);
+                $numberofmods = count($cmids);
+                for ($order = 0; $order < $numberofmods; $order++) {
+                    $cmid = $cmids[$order];
+                    // Activity not exist in database.
+                    $notexistindb = empty($rawmods[$cmid]);
+                    $activitycached = isset($mods[$cmid]);
+                    if ($activitycached || $notexistindb) {
+                        continue;
+                    }
+                    $modposition = ($order === 0) ? 0 : array_search($cmids[$order - 1], array_keys($mods)) + 1;
+                    $mods = array_slice($mods, 0, $modposition, true)
+                         + [$cmid => new stdClass()]
+                         + array_slice($mods, $modposition, null, true);
+
+                    // Adjust visibleoncoursepage, value in DB may not respect format availability.
+                    $rawmods[$cmid]->visibleoncoursepage = (!$rawmods[$cmid]->visible
+                           || $rawmods[$cmid]->visibleoncoursepage
+                           || empty($CFG->allowstealth)
+                           || !$courseformat->allow_stealth_module_visibility($rawmods[$cmid], $section)) ? 1 : 0;
+
+                    $mods[$cmid]->id = $rawmods[$cmid]->instance;
+                    $mods[$cmid]->cm = $rawmods[$cmid]->id;
+                    $mods[$cmid]->mod = $rawmods[$cmid]->modname;
 
                     // Oh dear. Inconsistent names left here for backward compatibility.
-                   $mod[$seq]->section          = $section->section;
-                   $mod[$seq]->sectionid        = $rawmods[$seq]->section;
+                    $mods[$cmid]->section = $section->section;
+                    $mods[$cmid]->sectionid = $rawmods[$cmid]->section;
 
-                   $mod[$seq]->module           = $rawmods[$seq]->module;
-                   $mod[$seq]->added            = $rawmods[$seq]->added;
-                   $mod[$seq]->score            = $rawmods[$seq]->score;
-                   $mod[$seq]->idnumber         = $rawmods[$seq]->idnumber;
-                   $mod[$seq]->visible          = $rawmods[$seq]->visible;
-                   $mod[$seq]->visibleoncoursepage = $rawmods[$seq]->visibleoncoursepage;
-                   $mod[$seq]->visibleold       = $rawmods[$seq]->visibleold;
-                   $mod[$seq]->groupmode        = $rawmods[$seq]->groupmode;
-                   $mod[$seq]->groupingid       = $rawmods[$seq]->groupingid;
-                   $mod[$seq]->indent           = $rawmods[$seq]->indent;
-                   $mod[$seq]->completion       = $rawmods[$seq]->completion;
-                   $mod[$seq]->extra            = "";
-                   $mod[$seq]->completiongradeitemnumber =
-                           $rawmods[$seq]->completiongradeitemnumber;
-                   $mod[$seq]->completionpassgrade = $rawmods[$seq]->completionpassgrade;
-                   $mod[$seq]->completionview   = $rawmods[$seq]->completionview;
-                   $mod[$seq]->completionexpected = $rawmods[$seq]->completionexpected;
-                   $mod[$seq]->showdescription  = $rawmods[$seq]->showdescription;
-                   $mod[$seq]->availability = $rawmods[$seq]->availability;
-                   $mod[$seq]->deletioninprogress = $rawmods[$seq]->deletioninprogress;
+                    $mods[$cmid]->module = $rawmods[$cmid]->module;
+                    $mods[$cmid]->added = $rawmods[$cmid]->added;
+                    $mods[$cmid]->score = $rawmods[$cmid]->score;
+                    $mods[$cmid]->idnumber = $rawmods[$cmid]->idnumber;
+                    $mods[$cmid]->visible = $rawmods[$cmid]->visible;
+                    $mods[$cmid]->visibleoncoursepage = $rawmods[$cmid]->visibleoncoursepage;
+                    $mods[$cmid]->visibleold = $rawmods[$cmid]->visibleold;
+                    $mods[$cmid]->groupmode = $rawmods[$cmid]->groupmode;
+                    $mods[$cmid]->groupingid = $rawmods[$cmid]->groupingid;
+                    $mods[$cmid]->indent = $rawmods[$cmid]->indent;
+                    $mods[$cmid]->completion = $rawmods[$cmid]->completion;
+                    $mods[$cmid]->extra = "";
+                    $mods[$cmid]->completiongradeitemnumber =
+                           $rawmods[$cmid]->completiongradeitemnumber;
+                    $mods[$cmid]->completionpassgrade = $rawmods[$cmid]->completionpassgrade;
+                    $mods[$cmid]->completionview = $rawmods[$cmid]->completionview;
+                    $mods[$cmid]->completionexpected = $rawmods[$cmid]->completionexpected;
+                    $mods[$cmid]->showdescription = $rawmods[$cmid]->showdescription;
+                    $mods[$cmid]->availability = $rawmods[$cmid]->availability;
+                    $mods[$cmid]->deletioninprogress = $rawmods[$cmid]->deletioninprogress;
 
-                   $modname = $mod[$seq]->mod;
-                   $functionname = $modname."_get_coursemodule_info";
+                    $modname = $mods[$cmid]->mod;
+                    $functionname = $modname . "_get_coursemodule_info";
 
-                   if (!file_exists("$CFG->dirroot/mod/$modname/lib.php")) {
-                       continue;
-                   }
+                    if (!file_exists("$CFG->dirroot/mod/$modname/lib.php")) {
+                        continue;
+                    }
 
-                   include_once("$CFG->dirroot/mod/$modname/lib.php");
+                    include_once("$CFG->dirroot/mod/$modname/lib.php");
 
-                   if ($hasfunction = function_exists($functionname)) {
-                       if ($info = $functionname($rawmods[$seq])) {
-                           if (!empty($info->icon)) {
-                               $mod[$seq]->icon = $info->icon;
-                           }
-                           if (!empty($info->iconcomponent)) {
-                               $mod[$seq]->iconcomponent = $info->iconcomponent;
-                           }
-                           if (!empty($info->name)) {
-                               $mod[$seq]->name = $info->name;
-                           }
-                           if ($info instanceof cached_cm_info) {
-                               // When using cached_cm_info you can include three new fields
-                               // that aren't available for legacy code
-                               if (!empty($info->content)) {
-                                   $mod[$seq]->content = $info->content;
-                               }
-                               if (!empty($info->extraclasses)) {
-                                   $mod[$seq]->extraclasses = $info->extraclasses;
-                               }
-                               if (!empty($info->iconurl)) {
-                                   // Convert URL to string as it's easier to store. Also serialized object contains \0 byte and can not be written to Postgres DB.
-                                   $url = new moodle_url($info->iconurl);
-                                   $mod[$seq]->iconurl = $url->out(false);
-                               }
-                               if (!empty($info->onclick)) {
-                                   $mod[$seq]->onclick = $info->onclick;
-                               }
-                               if (!empty($info->customdata)) {
-                                   $mod[$seq]->customdata = $info->customdata;
-                               }
-                           } else {
-                               // When using a stdclass, the (horrible) deprecated ->extra field
-                               // is available for BC
-                               if (!empty($info->extra)) {
-                                   $mod[$seq]->extra = $info->extra;
-                               }
-                           }
-                       }
-                   }
-                   // When there is no modname_get_coursemodule_info function,
-                   // but showdescriptions is enabled, then we use the 'intro'
-                   // and 'introformat' fields in the module table
-                   if (!$hasfunction && $rawmods[$seq]->showdescription) {
-                       if ($modvalues = $DB->get_record($rawmods[$seq]->modname,
-                               array('id' => $rawmods[$seq]->instance), 'name, intro, introformat')) {
-                           // Set content from intro and introformat. Filters are disabled
-                           // because we  filter it with format_text at display time
-                           $mod[$seq]->content = format_module_intro($rawmods[$seq]->modname,
-                                   $modvalues, $rawmods[$seq]->id, false);
+                    if ($hasfunction = function_exists($functionname)) {
+                        if ($info = $functionname($rawmods[$cmid])) {
+                            if (!empty($info->icon)) {
+                                $mods[$cmid]->icon = $info->icon;
+                            }
+                            if (!empty($info->iconcomponent)) {
+                                $mods[$cmid]->iconcomponent = $info->iconcomponent;
+                            }
+                            if (!empty($info->name)) {
+                                $mods[$cmid]->name = $info->name;
+                            }
+                            if ($info instanceof cached_cm_info) {
+                                // When using cached_cm_info you can include three new fields.
+                                // That aren't available for legacy code.
+                                if (!empty($info->content)) {
+                                    $mods[$cmid]->content = $info->content;
+                                }
+                                if (!empty($info->extraclasses)) {
+                                    $mods[$cmid]->extraclasses = $info->extraclasses;
+                                }
+                                if (!empty($info->iconurl)) {
+                                    // Convert URL to string as it's easier to store.
+                                    // Also serialized object contains \0 byte,
+                                    // ... and can not be written to Postgres DB.
+                                    $url = new moodle_url($info->iconurl);
+                                    $mods[$cmid]->iconurl = $url->out(false);
+                                }
+                                if (!empty($info->onclick)) {
+                                    $mods[$cmid]->onclick = $info->onclick;
+                                }
+                                if (!empty($info->customdata)) {
+                                    $mods[$cmid]->customdata = $info->customdata;
+                                }
+                            } else {
+                                // When using a stdclass, the (horrible) deprecated ->extra field,
+                                // ... that is available for BC.
+                                if (!empty($info->extra)) {
+                                    $mods[$cmid]->extra = $info->extra;
+                                }
+                            }
+                        }
+                    }
+                    // When there is no modname_get_coursemodule_info function,
+                    // ... but showdescriptions is enabled, then we use the 'intro',
+                    // ... and 'introformat' fields in the module table.
+                    if (!$hasfunction && $rawmods[$cmid]->showdescription) {
+                        if ($modvalues = $DB->get_record($rawmods[$cmid]->modname,
+                               ['id' => $rawmods[$cmid]->instance], 'name, intro, introformat')) {
+                            // Set content from intro and introformat. Filters are disabled.
+                            // Because we filter it with format_text at display time.
+                            $mods[$cmid]->content = format_module_intro($rawmods[$cmid]->modname,
+                                   $modvalues, $rawmods[$cmid]->id, false);
 
-                           // To save making another query just below, put name in here
-                           $mod[$seq]->name = $modvalues->name;
-                       }
-                   }
-                   if (!isset($mod[$seq]->name)) {
-                       $mod[$seq]->name = $DB->get_field($rawmods[$seq]->modname, "name", array("id"=>$rawmods[$seq]->instance));
-                   }
+                            // To save making another query just below, put name in here.
+                            $mods[$cmid]->name = $modvalues->name;
+                        }
+                    }
+                    if (!isset($mods[$cmid]->name)) {
+                        $mods[$cmid]->name = $DB->get_field($rawmods[$cmid]->modname, "name",
+                            ["id" => $rawmods[$cmid]->instance]);
+                    }
 
-                    // Minimise the database size by unsetting default options when they are
-                    // 'empty'. This list corresponds to code in the cm_info constructor.
-                    foreach (array('idnumber', 'groupmode', 'groupingid',
+                    // Minimise the database size by unsetting default options when they are 'empty'.
+                    // This list corresponds to code in the cm_info constructor.
+                    foreach (['idnumber', 'groupmode', 'groupingid',
                             'indent', 'completion', 'extra', 'extraclasses', 'iconurl', 'onclick', 'content',
                             'icon', 'iconcomponent', 'customdata', 'availability', 'completionview',
-                            'completionexpected', 'score', 'showdescription', 'deletioninprogress') as $property) {
-                       if (property_exists($mod[$seq], $property) &&
-                               empty($mod[$seq]->{$property})) {
-                           unset($mod[$seq]->{$property});
-                       }
-                   }
-                   // Special case: this value is usually set to null, but may be 0
-                   if (property_exists($mod[$seq], 'completiongradeitemnumber') &&
-                           is_null($mod[$seq]->completiongradeitemnumber)) {
-                       unset($mod[$seq]->completiongradeitemnumber);
-                   }
-               }
+                            'completionexpected', 'score', 'showdescription', 'deletioninprogress'] as $property) {
+                        if (property_exists($mods[$cmid], $property) &&
+                               empty($mods[$cmid]->{$property})) {
+                            unset($mods[$cmid]->{$property});
+                        }
+                    }
+                    // Special case: this value is usually set to null, but may be 0.
+                    if (property_exists($mods[$cmid], 'completiongradeitemnumber') &&
+                           is_null($mods[$cmid]->completiongradeitemnumber)) {
+                        unset($mods[$cmid]->completiongradeitemnumber);
+                    }
+                }
             }
         }
     }
-    return $mod;
+    return $mods;
 }
 
 /**
@@ -814,11 +839,7 @@ function course_add_cm_to_section($courseorid, $cmid, $sectionnum, $beforemod =
     }
     $DB->set_field("course_sections", "sequence", $newsequence, array("id" => $section->id));
     $DB->set_field('course_modules', 'section', $section->id, array('id' => $cmid));
-    if (is_object($courseorid)) {
-        rebuild_course_cache($courseorid->id, true);
-    } else {
-        rebuild_course_cache($courseorid, true);
-    }
+    rebuild_course_cache($courseid, true);
     return $section->id;     // Return course_sections ID that was used.
 }
 
@@ -837,7 +858,8 @@ function set_coursemodule_groupmode($id, $groupmode) {
     $cm = $DB->get_record('course_modules', array('id' => $id), 'id,course,groupmode', MUST_EXIST);
     if ($cm->groupmode != $groupmode) {
         $DB->set_field('course_modules', 'groupmode', $groupmode, array('id' => $cm->id));
-        rebuild_course_cache($cm->course, true);
+        course_purge_module_cache($cm);
+        rebuild_course_cache($cm->course, false, true);
     }
     return ($cm->groupmode != $groupmode);
 }
@@ -847,7 +869,8 @@ function set_coursemodule_idnumber($id, $idnumber) {
     $cm = $DB->get_record('course_modules', array('id' => $id), 'id,course,idnumber', MUST_EXIST);
     if ($cm->idnumber != $idnumber) {
         $DB->set_field('course_modules', 'idnumber', $idnumber, array('id' => $cm->id));
-        rebuild_course_cache($cm->course, true);
+        course_purge_module_cache($cm);
+        rebuild_course_cache($cm->course, false, true);
     }
     return ($cm->idnumber != $idnumber);
 }
@@ -924,7 +947,8 @@ function set_coursemodule_visible($id, $visible, $visibleoncoursepage = 1) {
         }
     }
 
-    rebuild_course_cache($cm->course, true);
+    course_purge_module_cache($cm);
+    rebuild_course_cache($cm->course, false, true);
     return true;
 }
 
@@ -961,7 +985,8 @@ function set_coursemodule_name($id, $name) {
     $DB->update_record($cm->modname, $module);
     $cm->name = $module->name;
     \core\event\course_module_updated::create_from_cm($cm)->trigger();
-    rebuild_course_cache($cm->course, true);
+    course_purge_module_cache($cm);
+    rebuild_course_cache($cm->course, false, true);
 
     // Attempt to update the grade item if relevant.
     $grademodule = $DB->get_record($cm->modname, array('id' => $cm->instance));
@@ -1113,13 +1138,14 @@ function course_delete_module($cmid, $async = false) {
         'context'  => $modcontext,
         'objectid' => $cm->id,
         'other'    => array(
-            'modulename' => $modulename,
+            'modulename'   => $modulename,
             'instanceid'   => $cm->instance,
         )
     ));
     $event->add_record_snapshot('course_modules', $cm);
     $event->trigger();
-    rebuild_course_cache($cm->course, true);
+    course_purge_module_cache($cm);
+    rebuild_course_cache($cm->course, false, true);
 }
 
 /**
@@ -1376,17 +1402,23 @@ function move_section_to($course, $section, $destination, $ignorenumsections = f
 
     $movedsections = reorder_sections($sections, $section, $destination);
 
+    $sectioninfo = new stdClass;
+    $sectioninfo->course = $course->id;
     // Update all sections. Do this in 2 steps to avoid breaking database
     // uniqueness constraint
     $transaction = $DB->start_delegated_transaction();
     foreach ($movedsections as $id => $position) {
         if ($sections[$id] !== $position) {
-            $DB->set_field('course_sections', 'section', -$position, array('id' => $id));
+            $DB->set_field('course_sections', 'section', -$position, ['id' => $id]);
+            $sectioninfo->section = $id;
+            course_purge_section_cache($sectioninfo);
         }
     }
     foreach ($movedsections as $id => $position) {
         if ($sections[$id] !== $position) {
-            $DB->set_field('course_sections', 'section', $position, array('id' => $id));
+            $DB->set_field('course_sections', 'section', $position, ['id' => $id]);
+            $sectioninfo->section = $id;
+            course_purge_section_cache($sectioninfo);
         }
     }
 
@@ -1394,14 +1426,14 @@ function move_section_to($course, $section, $destination, $ignorenumsections = f
     // Adjust the higlighted section location if we move something over it either direction.
     if ($section == $course->marker) {
         course_set_marker($course->id, $destination);
-    } elseif ($section > $course->marker && $course->marker >= $destination) {
+    } else if ($section > $course->marker && $course->marker >= $destination) {
         course_set_marker($course->id, $course->marker+1);
-    } elseif ($section < $course->marker && $course->marker <= $destination) {
+    } else if ($section < $course->marker && $course->marker <= $destination) {
         course_set_marker($course->id, $course->marker-1);
     }
 
     $transaction->allow_commit();
-    rebuild_course_cache($course->id, true);
+    rebuild_course_cache($course->id, true, true);
     return true;
 }
 
@@ -1576,7 +1608,8 @@ function course_update_section($course, $section, $data) {
     $data['id'] = $section->id;
     $data['timemodified'] = time();
     $DB->update_record('course_sections', $data);
-    rebuild_course_cache($courseid, true);
+    course_purge_section_cache($section);
+    rebuild_course_cache($courseid, false, true);
     course_get_format($courseid)->update_section_format_options($data);
 
     // Update fields of the $section object.
@@ -1608,11 +1641,13 @@ function course_update_section($course, $section, $data) {
                 } else {
                     // We hide the section, so we hide the module but we store the original state in visibleold.
                     set_coursemodule_visible($moduleid, 0, $cm->visibleoncoursepage);
-                    $DB->set_field('course_modules', 'visibleold', $cm->visible, array('id' => $moduleid));
+                    $DB->set_field('course_modules', 'visibleold', $cm->visible, ['id' => $moduleid]);
+                    course_purge_module_cache($cm);
                 }
                 \core\event\course_module_updated::create_from_cm($cm)->trigger();
             }
         }
+        rebuild_course_cache($courseid, false, true);
     }
 }
 
@@ -5130,3 +5165,50 @@ function course_output_fragment_new_base_form($args) {
 
     return $o;
 }
+
+/**
+ * Purge the cache of a course section.
+ *
+ * $sectioninfo must have following attributes:
+ *   - course: course id
+ *   - section: section number
+ *
+ * @param object $sectioninfo section info
+ * @return void
+ */
+function course_purge_section_cache(object $sectioninfo): void {
+    $section = $sectioninfo->section;
+    $courseid = $sectioninfo->course;
+    $cache = cache::make('core', 'coursemodinfo');
+    $cache->acquire_lock($courseid);
+    $coursemodinfo = $cache->get($courseid);
+    if (($coursemodinfo !== false) && array_key_exists($section, $coursemodinfo->sectioncache)) {
+        unset($coursemodinfo->sectioncache[$section]);
+        $cache->set($courseid, $coursemodinfo);
+    }
+    $cache->release_lock($courseid);
+}
+
+/**
+ * Purge the cache of a course module.
+ *
+ * $cm must have following attributes:
+ *   - id: cmid
+ *   - course: course id
+ *
+ * @param cm_info|stdClass $cm course module
+ * @return void
+ */
+function course_purge_module_cache($cm): void {
+    $cmid = $cm->id;
+    $courseid = $cm->course;
+    $cache = cache::make('core', 'coursemodinfo');
+    $cache->acquire_lock($courseid);
+    $coursemodinfo = $cache->get($courseid);
+    $hascache = ($coursemodinfo !== false) && array_key_exists($cmid, $coursemodinfo->modinfo);
+    if ($hascache) {
+        unset($coursemodinfo->modinfo[$cmid]);
+        $cache->set($courseid, $coursemodinfo);
+    }
+    $cache->release_lock($courseid);
+}
diff --git a/course/mod.php b/course/mod.php
index 67719a7aae2..86fc2bfcda5 100644
--- a/course/mod.php
+++ b/course/mod.php
@@ -190,7 +190,9 @@ if ((!empty($movetosection) or !empty($moveto)) and confirm_sesskey()) {
 
     $DB->set_field('course_modules', 'indent', $cm->indent, array('id'=>$cm->id));
 
-    rebuild_course_cache($cm->course);
+    course_purge_module_cache($cm);
+    // Rebuild invalidated module cache.
+    rebuild_course_cache($cm->course, false, true);
 
     redirect(course_get_url($course, $cm->sectionnum, array('sr' => $sectionreturn)));
 
diff --git a/course/modlib.php b/course/modlib.php
index 2afb5963cea..80e24b7b614 100644
--- a/course/modlib.php
+++ b/course/modlib.php
@@ -374,7 +374,11 @@ function edit_module_post_actions($moduleinfo, $course) {
         $moduleinfo->showgradingmanagement = $showgradingmanagement;
     }
 
-    rebuild_course_cache($course->id, true);
+    $cminfo = new stdClass();
+    $cminfo->course = $moduleinfo->course;
+    $cminfo->id = $moduleinfo->coursemodule;
+    course_purge_module_cache($cminfo);
+    rebuild_course_cache($course->id, true, true);
     if ($hasgrades) {
         grade_regrade_final_grades($course->id);
     }
diff --git a/course/tests/courselib_test.php b/course/tests/courselib_test.php
index 32f66639e07..9197e1a8ac6 100644
--- a/course/tests/courselib_test.php
+++ b/course/tests/courselib_test.php
@@ -1099,6 +1099,7 @@ class core_course_courselib_testcase extends advanced_testcase {
 
         // Delete section in the middle (2).
         $this->assertFalse(course_delete_section($course, 2, false));
+        $this->assertEquals(4, course_get_format($course)->get_last_section_number());
         $this->assertTrue(course_delete_section($course, 2, true));
         $this->assertFalse($DB->record_exists('course_modules', array('id' => $assign21->cmid)));
         $this->assertFalse($DB->record_exists('course_modules', array('id' => $assign22->cmid)));
diff --git a/course/tests/externallib_test.php b/course/tests/externallib_test.php
index 48650aa6cc7..03621e5cfe2 100644
--- a/course/tests/externallib_test.php
+++ b/course/tests/externallib_test.php
@@ -1085,8 +1085,9 @@ class externallib_test extends externallib_advanced_testcase {
             array('course' => $course->id, 'intro' => 'forum completion tracking auto', 'trackingtype' => 2),
             array('showdescription' => true, 'completionview' => 1, 'completion' => COMPLETION_TRACKING_AUTOMATIC));
         $forumcompleteautocm = get_coursemodule_from_id('forum', $forumcompleteauto->cmid);
-
-        rebuild_course_cache($course->id, true);
+        $sectionrecord = $DB->get_record('course_sections', $conditions);
+        course_purge_section_cache($sectionrecord);
+        rebuild_course_cache($course->id, true, true);
 
         return array($course, $forumcm, $datacm, $pagecm, $labelcm, $urlcm, $forumcompleteautocm);
     }
diff --git a/lib/db/caches.php b/lib/db/caches.php
index 5fabc3bbfb3..80f6d189f60 100644
--- a/lib/db/caches.php
+++ b/lib/db/caches.php
@@ -221,8 +221,16 @@ $definitions = array(
         'simplekeys' => true,
         'ttl' => 3600,
     ),
-    // Accumulated information about course modules and sections used to print course view page (user-independed).
-    // Used in function get_fast_modinfo(), reset in function rebuild_course_cache().
+    // Accumulated information about course modules and sections used to print course view page (user-independent).
+    // Used in functions:
+    // - course_modinfo::build_course_section_cache()
+    // - course_modinfo::inner_build_course_cache()
+    // - get_array_of_activities()
+    // Reset/update in functions:
+    // - rebuild_course_cache()
+    // - course_purge_module_cache()
+    // - course_purge_section_cache()
+    // - remove_course_contents().
     'coursemodinfo' => array(
         'mode' => cache_store::MODE_APPLICATION,
         'simplekeys' => true,
diff --git a/lib/modinfolib.php b/lib/modinfolib.php
index 191e5e062a6..a29078654ff 100644
--- a/lib/modinfolib.php
+++ b/lib/modinfolib.php
@@ -514,7 +514,7 @@ class course_modinfo {
                             ' does not have context. Rebuilding cache for course '. $course->id);
                     // Re-request the course record from DB as well, don't use get_course() here.
                     $course = $DB->get_record('course', array('id' => $course->id), '*', MUST_EXIST);
-                    $coursemodinfo = self::build_course_cache($course);
+                    $coursemodinfo = self::build_course_cache($course, true);
                     break;
                 }
             }
@@ -553,6 +553,7 @@ class course_modinfo {
                 $this->instances[$cm->modname] = array();
             }
             $this->instances[$cm->modname][$cm->instance] = $cm;
+            ksort($this->instances[$cm->modname]);
             $this->cms[$cm->id] = $cm;
 
             // Reconstruct sections. This works because modules are stored in order
@@ -562,6 +563,8 @@ class course_modinfo {
             $this->sections[$cm->sectionnum][] = $cm->id;
         }
 
+        ksort($this->cms);
+        ksort($this->instances);
         // Expand section objects
         $this->sectioninfo = array();
         foreach ($coursemodinfo->sectioncache as $number => $data) {
@@ -588,23 +591,37 @@ class course_modinfo {
      * in some other way.)
      *
      * @param stdClass $course Course object (must contain fields
+     * @param boolean $usecache use cached section info if exists, use true for partial course rebuild
      * @return array Information about sections, indexed by section number (not id)
      */
-    protected static function build_course_section_cache($course) {
+    protected static function build_course_section_cache(\stdClass $course, bool $usecache = false): array {
         global $DB;
 
         // Get section data
         $sections = $DB->get_records('course_sections', array('course' => $course->id), 'section',
                 'section, id, course, name, summary, summaryformat, sequence, visible, availability');
-        $compressedsections = array();
+        $compressedsections = [];
+        $courseformat = course_get_format($course);
+
+        if ($usecache) {
+            $cachecoursemodinfo = \cache::make('core', 'coursemodinfo');
+            $coursemodinfo = $cachecoursemodinfo->get($course->id);
+            if ($coursemodinfo !== false) {
+                $compressedsections = $coursemodinfo->sectioncache;
+            }
+        }
 
         $formatoptionsdef = course_get_format($course)->section_format_options();
         // Remove unnecessary data and add availability
         foreach ($sections as $number => $section) {
+            $sectioninfocached = isset($compressedsections[$number]);
+            if ($sectioninfocached) {
+                continue;
+            }
             // Add cached options from course format to $section object
             foreach ($formatoptionsdef as $key => $option) {
                 if (!empty($option['cache'])) {
-                    $formatoptions = course_get_format($course)->get_format_options($section);
+                    $formatoptions = $courseformat->get_format_options($section);
                     if (!array_key_exists('cachedefault', $option) || $option['cachedefault'] !== $formatoptions[$key]) {
                         $section->$key = $formatoptions[$key];
                     }
@@ -615,6 +632,7 @@ class course_modinfo {
             section_info::convert_for_section_cache($compressedsections[$number]);
         }
 
+        ksort($compressedsections);
         return $compressedsections;
     }
 
@@ -652,19 +670,20 @@ class course_modinfo {
      *
      * @param stdClass $course object from DB table course. Must have property 'id'
      *     but preferably should have all cached fields.
+     * @param boolean $partialrebuild Indicates it's partial course rebuild or not
      * @return stdClass object with all cached keys of the course plus fields modinfo and sectioncache.
      *     The same object is stored in MUC
      * @throws moodle_exception if course is not found (if $course object misses some of the
      *     necessary fields it is re-requested from database)
      */
-    public static function build_course_cache($course) {
+    public static function build_course_cache(\stdClass $course, bool $partialrebuild = false): \stdClass {
         if (empty($course->id)) {
             throw new coding_exception('Object $course is missing required property \id\'');
         }
 
         $lock = self::get_course_cache_lock($course->id);
         try {
-            return self::inner_build_course_cache($course, $lock);
+            return self::inner_build_course_cache($course, $lock, $partialrebuild);
         } finally {
             $lock->release();
         }
@@ -675,9 +694,11 @@ class course_modinfo {
      *
      * @param stdClass $course object from DB table course
      * @param \core\lock\lock $lock Lock object - not actually used, just there to indicate you have a lock
+     * @param bool $partialrebuild Is partial rebuild or not
      * @return stdClass Course object that has been stored in MUC
      */
-    protected static function inner_build_course_cache($course, \core\lock\lock $lock) {
+    protected static function inner_build_course_cache(\stdClass $course, \core\lock\lock $lock,
+            bool $partialrebuild = false): \stdClass {
         global $DB, $CFG;
         require_once("{$CFG->dirroot}/course/lib.php");
 
@@ -693,8 +714,8 @@ class course_modinfo {
         // This may take time on large courses and it is possible that another user modifies the same course during this process.
         // Field cacherev stored in both DB and cache will ensure that cached data matches the current course state.
         $coursemodinfo = new stdClass();
-        $coursemodinfo->modinfo = get_array_of_activities($course->id);
-        $coursemodinfo->sectioncache = self::build_course_section_cache($course);
+        $coursemodinfo->modinfo = get_array_of_activities($course->id, $partialrebuild);
+        $coursemodinfo->sectioncache = self::build_course_section_cache($course, $partialrebuild);
         foreach (self::$cachedfields as $key) {
             $coursemodinfo->$key = $course->$key;
         }
@@ -2415,9 +2436,22 @@ function get_course_and_cm_from_instance($instanceorid, $modulename, $courseorid
  * @param int $courseid id of course to rebuild, empty means all
  * @param boolean $clearonly only clear the cache, gets rebuild automatically on the fly.
  *     Recommended to set to true to avoid unnecessary multiple rebuilding.
+ * @param boolean $partialrebuild will not delete the whole cache when it's true.
+ *     use course_purge_module_cache() or course_purge_section_cache() must be
+ *         called before when partialrebuild is true.
+ *     use course_purge_module_cache() to invalidate mod cache.
+ *     use course_purge_section_cache() to invalidate section cache.
+ *
+ * @return void
+ * @throws coding_exception
  */
-function rebuild_course_cache($courseid=0, $clearonly=false) {
-    global $COURSE, $SITE, $DB, $CFG;
+function rebuild_course_cache(int $courseid = 0, bool $clearonly = false, bool $partialrebuild = false): void {
+    global $COURSE, $SITE, $DB;
+
+    if ($courseid == 0 and !empty($partialrebuild)) {
+        $error = 'partialrebuild only works when a valid course id is provided.';
+        throw new coding_exception($error);
+    }
 
     // Function rebuild_course_cache() can not be called during upgrade unless it's clear only.
     if (!$clearonly && !upgrade_ensure_not_running(true)) {
@@ -2433,7 +2467,10 @@ function rebuild_course_cache($courseid=0, $clearonly=false) {
     if (empty($courseid)) {
         // Clearing caches for all courses.
         increment_revision_number('course', 'cacherev', '');
-        $cachecoursemodinfo->purge();
+        if (!$partialrebuild) {
+            $cachecoursemodinfo->purge();
+        }
+        // Clear memory static cache.
         course_modinfo::clear_instance_cache();
         // Update global values too.
         $sitecacherev = $DB->get_field('course', 'cacherev', array('id' => SITEID));
@@ -2446,7 +2483,11 @@ function rebuild_course_cache($courseid=0, $clearonly=false) {
     } else {
         // Clearing cache for one course, make sure it is deleted from user request cache as well.
         increment_revision_number('course', 'cacherev', 'id = :id', array('id' => $courseid));
-        $cachecoursemodinfo->delete($courseid);
+        if (!$partialrebuild) {
+            // Purge all course modinfo.
+            $cachecoursemodinfo->delete($courseid);
+        }
+        // Clear memory static cache.
         course_modinfo::clear_instance_cache($courseid);
         // Update global values too.
         if ($courseid == $COURSE->id || $courseid == $SITE->id) {
@@ -2471,10 +2512,13 @@ function rebuild_course_cache($courseid=0, $clearonly=false) {
         core_php_time_limit::raise();  // this could take a while!   MDL-10954
     }
 
-    $rs = $DB->get_recordset("course", $select,'','id,'.join(',', course_modinfo::$cachedfields));
+    $fields = 'id,' . join(',', course_modinfo::$cachedfields);
+    $sort = '';
+    $rs = $DB->get_recordset("course", $select, $sort, $fields);
+
     // Rebuild cache for each course.
     foreach ($rs as $course) {
-        course_modinfo::build_course_cache($course);
+        course_modinfo::build_course_cache($course, $partialrebuild);
     }
     $rs->close();
 }
diff --git a/lib/tests/modinfolib_test.php b/lib/tests/modinfolib_test.php
index 0f6222871c2..97fa7cd76c6 100644
--- a/lib/tests/modinfolib_test.php
+++ b/lib/tests/modinfolib_test.php
@@ -365,7 +365,7 @@ class modinfolib_test extends advanced_testcase {
         $this->assertEquals($USER->id, $modinfo->userid);
         $this->assertEquals(array(0 => array($forum0->cmid, $assign0->cmid),
             1 => array($forum1->cmid, $assign1->cmid, $page1->cmid), 3 => array($page3->cmid)), $modinfo->sections);
-        $this->assertEquals(array('forum', 'assign', 'page'), array_keys($modinfo->instances));
+        $this->assertEquals(array('assign', 'forum', 'page'), array_keys($modinfo->instances));
         $this->assertEquals(array($assign0->id, $assign1->id), array_keys($modinfo->instances['assign']));
         $this->assertEquals(array($forum0->id, $forum1->id), array_keys($modinfo->instances['forum']));
         $this->assertEquals(array($page1->id, $page3->id), array_keys($modinfo->instances['page']));
diff --git a/lib/upgrade.txt b/lib/upgrade.txt
index 971a378ca0e..371ab500cab 100644
--- a/lib/upgrade.txt
+++ b/lib/upgrade.txt
@@ -25,7 +25,8 @@ information provided here is intended especially for developers.
 * The completion_info function display_help_icon() which returned the 'Your progress' help icon has been deprecated and
   should no longer be used.
 * The completion_info function print_help_icon() which has been deprecated since Moodle 2.0 should no longer be used.
-* @babel/polyfill has been removed in favour of corejs@3
+* @babel/polyfill has been removed in favour of corejs@3.
+* A new parameter $partialrebuild has been added to the rebuild_course_cache.
 * A new parameter $isbulkupdate has been added to the following functions:
   - grade_category::update()
   - grade_category::insert()
diff --git a/mod/chat/lib.php b/mod/chat/lib.php
index 06abf29fc9f..e742d2dce40 100644
--- a/mod/chat/lib.php
+++ b/mod/chat/lib.php
@@ -713,6 +713,9 @@ function chat_update_chat_times($chatid=0) {
         $cond = "modulename='chat' AND eventtype = :eventtype AND instance = :chatid AND timestart <> :chattime";
         $params = ['chattime' => $chat->chattime, 'eventtype' => CHAT_EVENT_TYPE_CHATTIME, 'chatid' => $chat->id];
 
+        $cm = get_coursemodule_from_instance('chat', $chat->id, $chat->course);
+        course_purge_module_cache($cm);
+
         if ($event->id = $DB->get_field_select('event', 'id', $cond, $params)) {
             $event->timestart = $chat->chattime;
             $event->timesort = $chat->chattime;
@@ -723,7 +726,7 @@ function chat_update_chat_times($chatid=0) {
 
     $courseids = array_unique($courseids);
     foreach ($courseids as $courseid) {
-        rebuild_course_cache($courseid, true);
+        rebuild_course_cache($courseid, true, true);
     }
 }
 
diff --git a/mod/lti/locallib.php b/mod/lti/locallib.php
index b14a4cdddb7..03dc710144a 100644
--- a/mod/lti/locallib.php
+++ b/mod/lti/locallib.php
@@ -2833,14 +2833,23 @@ function lti_update_type($type, $config) {
         }
         require_once($CFG->libdir.'/modinfolib.php');
         if ($clearcache) {
-            $sql = "SELECT DISTINCT course
-                      FROM {lti}
-                     WHERE typeid = ?";
+            $sql = "SELECT cm.id, cm.course
+                      FROM {course_modules} cm
+                      JOIN {modules} m ON cm.module = m.id
+                      JOIN {lti} l ON l.course = cm.course
+                     WHERE m.name = :name AND l.typeid = :typeid";
 
-            $courses = $DB->get_fieldset_sql($sql, array($type->id));
+            $rs = $DB->get_recordset_sql($sql, ['name' => 'lti', 'typeid' => $type->id]);
 
-            foreach ($courses as $courseid) {
-                rebuild_course_cache($courseid, true);
+            $courseids = [];
+            foreach ($rs as $record) {
+                $courseids[] = $record->course;
+                course_purge_module_cache($record);
+            }
+            $rs->close();
+            $courseids = array_unique($courseids);
+            foreach ($courseids as $courseid) {
+                rebuild_course_cache($courseid, false, true);
             }
         }
     }