wordpress-performance

WordPress Performance

Performance optimization patterns for WordPress plugins, themes, and live sites.

Critical Rules

1. Never query without limits — posts_per_page => -1 and unbounded $wpdb queries are the most common cause of memory exhaustion on production sites.
2. Cache expensive queries — any query that runs on every page load and doesn't change per-request must be cached with transients or the object cache.
3. Use no_found_rows — set 'no_found_rows' => true on any WP_Query that doesn't need pagination; this skips SQL_CALC_FOUND_ROWS which is expensive on large tables.
4. Avoid meta queries on unindexed keys — meta_query on wp_postmeta performs full table scans unless you add custom indexes. Consider a custom table for heavily queried data.
5. Defer heavy work — operations on init run on every request. Use admin_init for admin-only work, rest_api_init for REST-only, and wp_loaded or later hooks when possible.
6. Prime caches, don't loop-query — use update_post_meta_cache(), update_post_caches(), or _prime_post_caches() to batch-load metadata instead of calling get_post_meta() in a loop.

Query Performance Patterns

Efficient WP_Query

// Good — limited, cache-friendly, no unnecessary data:
$query = new WP_Query( [
    'post_type'              => 'product',
    'posts_per_page'         => 20,
    'no_found_rows'          => true,   // Skip pagination count query.
    'update_post_meta_cache' => false,  // Skip if not reading meta.
    'update_post_term_cache' => false,  // Skip if not reading terms.
    'fields'                 => 'ids',  // Return only IDs when full objects aren't needed.
] );

// Bad — unbounded, forces full table scan:
$query = new WP_Query( [
    'post_type'      => 'product',
    'posts_per_page' => -1,  // Never do this.
] );

N+1 Query Prevention

// Bad — N+1 pattern (1 query per post in the loop):
foreach ( $posts as $post ) {
    $price = get_post_meta( $post->ID, '_price', true );  // Query per iteration.
}

// Good — prime the cache first, then loop reads from cache:
$post_ids = wp_list_pluck( $posts, 'ID' );
update_meta_cache( 'post', $post_ids );  // Single query loads all meta.

foreach ( $posts as $post ) {
    $price = get_post_meta( $post->ID, '_price', true );  // Reads from cache.
}