Out of the box ACF is taxing on your site performance, but also CPU load if you have large sites (think 10k+ posts). There are ways to improve ACF by doing things like batch writes or pre-fetching values into the ACF Store. As I create some of these techniques I will add them to this Gist. This will work okay'ish without an object cache, but its…

acf-hooks.php

<?php
/**
 * This file contains some hooks to improve ACF performance.
 *
 * @package rheinardkorf
 */

add_filter(
	'acf/pre_load_value',
	function( $meta, $post_id, $field ) {

		$store = acf_get_store( 'values' );

		// Prefetch options into ACF Store.
		if ( 'options' === $post_id ) {

			// Prefetch site options.
			if ( ! $store->has( 'prefetched:options' ) ) {
				global $wpdb;

				$like = 'option_%';

				$prefetch_cache_key = md5( 'acf/pre_load_value/prefetched:options' );
				$results            = wp_cache_get( $prefetch_cache_key );

				if ( empty( $results ) ) {
					$results = $wpdb->get_results( $wpdb->prepare( "SELECT * FROM $wpdb->options WHERE option_name LIKE %s", $like ) ); // phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery

					// Let the Object Cache LRU take care of expiry.
					wp_cache_set( $prefetch_cache_key, $results );
				}

				foreach ( $results as $result ) {
					$key = str_replace( 'options_', '', $result->option_name );
					$key = "options:$key";
					$store->set( $key, $result->option_value );
				}

				$store->set( 'prefetched:options', true );
			}
		} else {

			// Prefetch object meta.
			if ( ! $store->has( "prefetched:$post_id" ) ) {

				$decoded   = acf_decode_post_id( $post_id );
				$meta_id   = $decoded['id'];
				$meta_type = $decoded['type'];

				$prefetch_cache_key = md5( "acf/pre_load_value/prefetched:$post_id" );
				$meta_data          = wp_cache_get( $prefetch_cache_key );

				if ( empty( $meta_data ) ) {
					$meta_data = get_metadata( $meta_type, $meta_id );

					// Let the Object Cache LRU take care of expiry.
					wp_cache_set( $prefetch_cache_key, $meta_data );
				}

				foreach ( $meta_data as $field_name => $value ) {
					$real_value = is_array( $value ) && 1 === count( $value ) ? array_pop( $value ) : $value;
					// Ignore hidden keys.
					if ( preg_match( '/^_/', $field_name ) ) {
						continue;
					}
					$store->set( "$post_id:$field_name", $real_value );
				}

				$store->set( "prefetched:$post_id", true );
			}
		}

		// If value is already fetched then return that value.
		$field_name = $field['name'];
		if ( $store->has( "$post_id:$field_name" ) ) {
			return $store->get( "$post_id:$field_name" );
		}

		// Fallback.
		return $meta;
	},
	10,
	3
);