So, I want to use a relationship field in a block to allow the editor to choose some posts (from various post types).
But the admin / back-end performance is so bad that it’s basically unusable – it takes between 30 and 60 seconds before the field even becomes responsive and then more time to show the first set of posts in the left hand column.
I’ve set the number of posts returned in the AJAX query to 1, and that makes no difference. I suspect it’s taxonomy related (we have about 500 terms in the tags taxonomy), and if I disable the taxonomy filter in the relationship field, performance is fine.
So, what can be done to speed this up, or is the relationship field not usable with the taxonomy filter?
There has historically been a scaling issue when it comes to many of the relationship type fields. ACF is working within what is provided by WP. The taxonomy filter on the relationship field must get all of the taxonomies and then all of the terms in each taxonomy in order to sort them for the filter. This is also effected by the post types that can be filtered or the post type setting when filtering. This can be improved by limiting the post types and the taxonomies that appear in the filter. With a taxonomy with many terms in it has been reported that the request time out and showing no results. It may be necessary to limit the post types and not allow filtering by taxonomy on extremely large sites.