moodle-performance

Moodle Performance

Overview

Moodle bottlenecks: too many DB queries per request, full-table scans, loading large recordsets into memory, blocking work on the request path. Mitigations: MUC caching, indexes, recordsets, ad-hoc tasks, careful capability checks.

When to Use

• Page renders slowly / hits per-page query limits
• N+1 query pattern in loops
• Memory-blow on large datasets
• Long-running operations on POST handlers
• Tuning a custom report or scheduled task

Diagnosis

Performance debug

config.php:

$CFG->debug = (E_ALL | E_STRICT);
$CFG->debugdisplay = 1;
$CFG->perfdebug = 15;     // shows query count + timings in footer

Site admin > Development > Debugging > Performance info: enables the footer toolbar (queries, time, memory, MUC hits/misses, sessions reads/writes).

$PERF

global $PERF;
$start = microtime(true);
// ... work ...
$PERF->dbqueries++;       // your manual counter
mtrace('Took ' . round(microtime(true) - $start, 3) . 's');

Slow query log

Postgres / MySQL slow-query log — turn on in dev. Moodle prefixes queries with the source class via $CFG->dboptions['debug'].

MUC — Moodle Universal Cache

3 cache modes:

Mode	Storage	Lifetime	Use
MODE_APPLICATION	Persistent (file/Redis/Memcached)	Until invalidated	Shared computed values
MODE_SESSION	Session	Session lifetime	Per-user computed values
MODE_REQUEST	PHP request	Single request	Memoize within request

Define a cache

db/caches.php:

<?php
defined('MOODLE_INTERNAL') || die();

$definitions = [
    'active_announcements' => [
        'mode'         => cache_store::MODE_APPLICATION,
        'simplekeys'   => true,
        'simpledata'   => true,
        'ttl'          => 600,
        'invalidationevents' => ['changesin_local_announcements'],
    ],
    'user_dashboard' => [
        'mode'       => cache_store::MODE_SESSION,
        'simplekeys' => true,
    ],
];