Reduce batch size for WooCommerce Subscriptions upgrade process.

wcs-reduce-upgrade-batch-size.php

<?php
/**
 * Plugin Name: WooCommerce Subscriptions Reduce Upgrade Batch Size
 * Plugin URI:
 * Description: Drastically reduce the size of each batch of data WooCommerce Subscriptions upgrades per request. Handy to avoiding low script timeout settings on Nginx.
 * Author: Prospress Inc.
 * Version: 1.0
 * Author URI: http://prospress.com
 */
function eg_reduce_wcs_upgrade_batch_size( $batch_size ) {
	return ceil( $batch_size / 3 );
}
add_filter( 'woocommerce_subscriptions_hooks_to_upgrade', 'eg_reduce_wcs_upgrade_batch_size', 100 );
add_filter( 'woocommerce_subscriptions_to_upgrade', 'eg_reduce_wcs_upgrade_batch_size', 100 );