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  • Hi @geert

    Hard to know where to start…

    Okay, so most people on the web with a WordPress site probably has shared hosting (I’m guessing). They have little to no control over the servers settings and limitations. Here’s some standard PHP values which are unlikely to be set higher in such shared hosting:

    disclaimer: I’m not gonna research everything here before (limited time) so some is a little bit of guesswork when it comes to numbers.

    max_input_vars there is one of the most interesting ones. Basically it says that PHP will accept a maximum of 1000 input fields to send to a single request (page load). In the case of WP admin that would likely be a POST request. WordPress per default already have quite a bit of fields for a standard edit screen. There’s a whole bunch of hidden fields as well as formats, categories, tags, featured image, title, editor, permalink, visibility, status etc. Let’s say you also have a few regular custom fields. Then you also add a repeater field to this. Each row might contain 2-10 fields + some hidden fields ACF uses to keep track of everything. Maybe you even have nested repeaters! So for each row there’s 2-10 fields + a nested repeater which in term contains 2-10 fields. And say you add in a gallery field there as well. That’s at the very least 1 field for each image.

    You’re quickly gonna find that you hit the 1000 input vars limit if you abuse repeaters. That’s gonna stop you from adding any new content to the page before you delete other. That in itself should be enough to reconsider huge repeater fields. But to make matters worse there’s also server limits like max_execution_time and max_allowed_packet (mysql). Saving all these fields will take some time and if you’re not on a great internet connection you may hit the max_excecution_time which will lead to your page save ending abruptly and unfinished. max_allowed_packet is a variable for mySQL which basically limits how large of data chunk you may insert in one go. It’s much harder to hit but it’s possible.

    If you’d be on a VPS you could prevent all of this by just upping your server stats. However you’ll still get a very slow admin experience and let’s face it, you’re patching a leaking boat and probably have to pay a hefty price for it (big servers aren’t cheap).

    Then there’s also the issue of WordPress database structure and the performance of WP_Query. 10up has written a great article on performance with WP_Query and one of the things to avoid is post meta lookup. Usually there’s no choice BUT we can at least do what we can to use simple post meta like a single date field or a boolean. And of course try to minimize the amount of post meta for each single post.
    Consider that ACF adds two rows to wp_postmeta for each field (both regular and sub fields).

    So if we can refactor our data structure to use a custom post type which would contain some fields and then perhaps link different posts/post types together with the post object or relationship field we’ll end up with safer and quicker admin requests, faster and often more versatile use of wp_queries in our front end and a better DB structure more fitting of WordPress strengths and weaknesses.

    It’s hard to say a number of repeater rows that’d be “too much” since it depends on what they contain. But for me, if I find that I’d end up with more than 20-30 row of simpler repeater data or 10-15 rows of more complex ones I would consider a different solution. Sometimes it’s hard to predict tho. We’ve had customers where they were supposed to use repeaters for just a few categories of Press media attachments but they ended up dumping soooo much media there that we eventually had to rebuild it for them with a CPT where each post was a single media file and a taxonomy for the categories of media.

    Hope that was a sufficient answer 🙂