Performance issues, attachment_url_to_postid
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Hi there!
I’ve recently triaged a case where a site was experiencing some performance issues. The site was making excessive database queries, leading to very slow requests and throttling.
After examining things closer, we found that every image on each page and post were leading to a query for the image and various subsizes, like the following.
SELECT post_id, meta_value FROM wp_postmeta WHERE meta_key = '_wp_attached_file' AND meta_value = '2022/03/example-image.jpg' SELECT post_id, meta_value FROM wp_postmeta WHERE meta_key = '_wp_attached_file' AND meta_value = '2022/03/example-image-300x163.jpg' SELECT post_id, meta_value FROM wp_postmeta WHERE meta_key = '_wp_attached_file' AND meta_value = '2022/03/example-image-200x108.jpg' SELECT post_id, meta_value FROM wp_postmeta WHERE meta_key = '_wp_attached_file' AND meta_value = '2022/03/example-image-400x217.jpg'`Examining the stack trace for these requests led to this:
Patreon_Compatibility->jetpack_photon_skip_image, attachment_url_to_postidI see the plugin has a compatibility fixer to try to identify gated images and disable the Jetpack Photon Image CDN for them.
Note that this may lead to severe performance issues on sites with a lot of images and traffic. It may be worth reviewing further and finding a more optimized solution.
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We are experiencing the same issue. On some pages it even causes our pages to crash. Here is the response from the engineers at WordPress.com, where we host.
Hi there!
My colleagues let me know of the 429 errors you were encountering on the site at <domain>. Thank you for your patience while we continued to review this.
FindingsWe took a closer look and identified that our servers are operating normally; however, your site’s plugins and code are causing some performance issues.
While we will not be able to make server or developer adjustments to alleviate the issues your site is causing, I will provide information about our findings and potential next steps.
429 & 599 ErrorsThe 429s you’re encountering are not typical rate-limiting issues. While they appear as 429s to you and visitors, we log these internally as 599. I’ll refer to these as 599s throughout the rest of my message.
Rather than being normal 429s, your site is making many requests that are not optimized or performance. The requests are might be occurring too quickly, too often, and may be taking too long to complete due to code issues.
This leads to your site being limited temporarily until the pending requests are completed, timeout, or are generally reduced.
CausesThe 599s seem to have been caused by two primary situations
Users simply interacting with the site
Admins/editors making edits.It is the requests being made during these situations that lead to the rate-limiting. As mentioned, there are a number of performance issues that appear to be contributing to this and I will cover those next.
QueriesSome posts and pages on the site make an excessive number of queries.
Specifically, at times there may be hundreds of queries like the following running at the time time. This make for slow and unoptimized requests that can cause your site to utilize too many PHP connections.
SELECT post_id, meta_value FROM wp_postmeta WHERE meta_key = '_wp_attached_file' AND meta_value = '2019/05/Witchmothers-Potent-Brew-Food.jpg'We then see the same query for each subsize of the image. This results in hundreds of requests on a large majority of your pages.
Here is a stack track for what is generating the query.
require('wp-blog-header.php'), require_once('wp-includes/template-loader.php'), include('/themes/Avada/100-width.php'), the_content, apply_filters('the_content'), WP_Hook->apply_filters, do_shortcode, preg_replace_callback, do_shortcode_tag, FusionSC_Container->render, do_shortcode, preg_replace_callback, do_shortcode_tag, Fusion_Row_Element->render, do_shortcode, preg_replace_callback, do_shortcode_tag, Fusion_Column_Element->render, do_shortcode, preg_replace_callback, do_shortcode_tag, FusionSC_Imageframe->render, fusion_add_responsive_image_markup, wp_filter_content_tags, wp_img_tag_add_srcset_and_sizes_attr, wp_image_add_srcset_and_sizes, wp_calculate_image_srcset, apply_filters('wp_calculate_image_srcset'), WP_Hook->apply_filters, Jetpack_Photon->filter_srcset_array, apply_filters('jetpack_photon_skip_image'), WP_Hook->apply_filters, Patreon_Compatibility->jetpack_photon_skip_image, attachment_url_to_postidWhile examining this closer, we found that this seems to be a conflict between the `
Patreon WordPress plugin and our Image CDN. The content loads in, Avada (Fusion) Builder renders the image, and our Image CDN generates the necessary source set and subsizes.Then, the Patreon WordPress plugin performs some sort of compatibility check and “fix”, Patreon_Compatibility->jetpack_photon_skip_image, attachment_url_to_postid.
<strong>This is what then causes the excessive requests.</strong>
We recommend not using these two tools together for now and it may be necessary to contact the developer of the Patreon WordPress plugin if you find you would like to use our Image CDN again.
Next StepsTo help alleviate this, we’ve deactivated our Jetpack Image CDN module. This prevents the excessive number of requests Patreon WordPress would normally make without much, if any, negative impact on your content and performance.
If you would ever like to enable the Image CDN again, it can be toggled on by visiting My Site > Settings > Performance. There toggle on the button next to Speed up image load times. I do not recommend enabling this with the `Patreon WordPress plugin active. Not until they make changes to prevent this issue.
Your site hasn’t experienced 599s for the last few days and we have made some accommodations to assist with reducing load of server requests. With these changes, specifically the deactivation of the Image CDN, I would not expect this specific issue to occur again.
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