WordPress Performance Optimization (Caching, DB)

WordPress Performance Optimization (Caching, Database)

Default WordPress configuration is slow: each page request executes 30–100 SQL queries, loads dozens of plugins, and regenerates HTML from scratch. Proper optimization achieves Time to First Byte < 200 ms and Core Web Vitals in the green zone.

Audit: What's Slowing Things Down

Before optimization—measure. Tools:

• Query Monitor (plugin) — shows all SQL queries, hooks, slow queries per page
• New Relic or Tideways — PHP profiler for production
• GTmetrix / PageSpeed Insights — external metrics

Typical causes of slow performance:

1. No PHP OPcache
2. No object cache (Memcached/Redis)
3. Slow plugins (plugin ≠ culprit, but WP_Query inside—often)
4. wp_options table with thousands of autoload options
5. Huge wp_postmeta table
6. No page caching

PHP OPcache

# /etc/php/8.3/fpm/conf.d/10-opcache.ini
opcache.enable=1
opcache.memory_consumption=256
opcache.interned_strings_buffer=16
opcache.max_accelerated_files=10000
opcache.revalidate_freq=0          ; 0 in production (don't check changes)
opcache.validate_timestamps=0      ; 0 in production
opcache.fast_shutdown=1
opcache.jit=tracing
opcache.jit_buffer_size=64m

OPcache performance gain—30–50% reduction in PHP execution time.

Redis for Object Cache

apt install redis-server
# In WordPress
composer require wpackagist-plugin/redis-cache

wp-config.php:

define('WP_CACHE_KEY_SALT', 'yourdomain.com_');
define('WP_REDIS_HOST', '127.0.0.1');
define('WP_REDIS_PORT', 6379);
define('WP_REDIS_DATABASE', 0);
define('WP_REDIS_TIMEOUT', 1);
define('WP_REDIS_READ_TIMEOUT', 1);

Redis caches WP_Query results, options (get_option), user data. Repeated page request: with Redis—1–5 SQL queries instead of 30–100.

Page Caching

For high-load sites—Nginx FastCGI Cache (bypassing PHP entirely):

fastcgi_cache_path /var/cache/nginx/wordpress levels=1:2 keys_zone=WORDPRESS:100m inactive=60m;
fastcgi_cache_key "$scheme$request_method$host$request_uri";

server {
    location ~ \.php$ {
        fastcgi_cache WORDPRESS;
        fastcgi_cache_valid 200 301 302 60m;
        fastcgi_cache_bypass $skip_cache;
        fastcgi_no_cache $skip_cache;

        # Don't cache authorized users and shopping cart
        set $skip_cache 0;
        if ($http_cookie ~* "wordpress_logged_in|woocommerce_cart_hash") {
            set $skip_cache 1;
        }
        if ($request_method = POST) { set $skip_cache 1; }

        fastcgi_pass unix:/var/run/php/php8.3-fpm.sock;
        # ...
    }
}

Cached pages are served with TTFB < 10 ms.

Database Cleanup

-- Remove old revisions (keep last 5 per post)
DELETE p FROM wp_posts p
LEFT JOIN (
    SELECT ID FROM wp_posts
    WHERE post_type = 'revision'
    ORDER BY post_date DESC
    LIMIT 5
) keep ON p.ID = keep.ID
WHERE p.post_type = 'revision' AND keep.ID IS NULL;

-- Remove orphaned postmeta
DELETE pm FROM wp_postmeta pm
LEFT JOIN wp_posts p ON p.ID = pm.post_id
WHERE p.ID IS NULL;

-- Analyze autoload options (cause of slow get_option)
SELECT option_name, LENGTH(option_value) as size
FROM wp_options
WHERE autoload = 'yes'
ORDER BY size DESC
LIMIT 20;

-- Disable autoload for unnecessary options
UPDATE wp_options SET autoload = 'no'
WHERE option_name IN ('_transient_some_plugin_cache', 'some_large_option');

Image Optimization

// WebP conversion on upload (via Imagick)
add_filter('wp_handle_upload', function (array $upload): array {
    if (!str_starts_with($upload['type'], 'image/')) return $upload;

    $image = new Imagick($upload['file']);
    $image->setImageFormat('webp');
    $image->setOption('webp:lossless', 'false');
    $image->setCompressionQuality(82);

    $webp_path = preg_replace('/\.(jpe?g|png)$/i', '.webp', $upload['file']);
    $image->writeImage($webp_path);

    return $upload;
});

Or via ShortPixel / Imagify plugin with CDN integration.

Typical Optimization Results

Timeline

Basic optimization (OPcache, Redis, database cleanup, page cache)—2–3 days. Full audit with profiling and slow query optimization—5–7 days.