MDL-66253 calendar: New indexes to reduce full table scans

The eventtype index will stop full table scans when the Event API
retrieves events for a group or category and there are a large number
of groups or categories so it cannot use the groupid or categoryid
indexes efficiently.

The modulename-instance index will improve the performance of queries
used by activity backup, deletion and visibility changes where all
the events for an individual activity need to be found.

lib/db/install.xml

@@ -461,6 +461,8 @@
         <INDEX NAME="uuid" UNIQUE="false" FIELDS="uuid"/>
         <INDEX NAME="type-timesort" UNIQUE="false" FIELDS="type, timesort"/>
         <INDEX NAME="groupid-courseid-categoryid-visible-userid" UNIQUE="false" FIELDS="groupid, courseid, categoryid, visible, userid" COMMENT="used for calendar view"/>
+        <INDEX NAME="eventtype" UNIQUE="false" FIELDS="eventtype"/>
+        <INDEX NAME="modulename-instance" UNIQUE="false" FIELDS="modulename, instance"/>
       </INDEXES>
     </TABLE>
     <TABLE NAME="cache_filters" COMMENT="For keeping information about cached data">

lib/db/upgrade.php

@@ -2145,5 +2145,22 @@ function xmldb_main_upgrade($oldversion) {
         upgrade_main_savepoint(true, 2019122000.01);
     }
 
+    if ($oldversion < 2020010900.02) {
+        $table = new xmldb_table('event');
+
+        // This index will improve the performance when the Events API retrieves category and group events.
+        $index = new xmldb_index('eventtype', XMLDB_INDEX_NOTUNIQUE, ['eventtype']);
+        if (!$dbman->index_exists($table, $index)) {
+            $dbman->add_index($table, $index);
+        }
+
+        // This index improves the performance of backups, deletion and visibilty changes on activities.
+        $index = new xmldb_index('modulename-instance', XMLDB_INDEX_NOTUNIQUE, ['modulename', 'instance']);
+        if (!$dbman->index_exists($table, $index)) {
+            $dbman->add_index($table, $index);
+        }
+
+        upgrade_main_savepoint(true, 2020010900.02);
+    }
     return true;
 }

version.php

@@ -29,7 +29,7 @@
 
 defined('MOODLE_INTERNAL') || die();
 
-$version  = 2020010900.00;              // YYYYMMDD      = weekly release date of this DEV branch.
+$version  = 2020010900.01;              // YYYYMMDD      = weekly release date of this DEV branch.
                                         //         RR    = release increments - 00 in DEV branches.
                                         //           .XX = incremental changes.
 $release  = '3.9dev (Build: 20200109)'; // Human-friendly version name