I have been puzzling this out myself for a bit. I have a repeater field and each row of the repeater can have about 50 fields, many of them wysiwyg fields. Some of the posts have as many as 20 rows. This monster can actually timeout when you save a post. If I’d know this would happen I would have designed it differently.
The problem is not with ACF per-say. The problems is in the fact that WP can only insert or update a single custom field at a time. When you have a couple thousand fields that need to be updated it becomes ridiculously slow. I’ve been digging around in WP looking for a solutions. What I’d like to do is store all the upates and inserts and do them all at once. but $wpdb does not seem to have any way of doing multiple queries in one request.
