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Rendering queues

Prerender.io uses two queues to keep your cache fresh: a priority queue for urgent recache requests and a normal queue for routine refreshes.

TL;DR

Prerender.io recaches pages through two queues. The priority queue handles urgent recaches you trigger yourself (Recache API, sitemaps, manual Cache Manager actions). The normal queue recaches automatically based on your cache expiration setting, starting with the oldest pages. Your daily recache rate is roughly NUM_CACHED_PAGES / CACHE_EXPIRATION (in days). If a page returns anything other than 200 OK or 304 Not Modified during recache, it is removed from the cache. AI crawlers and search engines see a clean, current cache as a result.

 

Overview

Prerender.io uses two rendering queues, priority and normal, to manage how cached pages are refreshed over time. Together they keep your cached snapshots current so AI crawlers and search engines see fresh content, without you having to manually re-trigger renders. The queues process pages daily based on your cache freshness setting and your total cached URL count, so the recache work scales with your site size.

 

The priority queue

The priority queue handles urgent or user-initiated recache requests. It includes:

  • URLs submitted via the Recache API.
  • Pages listed in your Sitemaps.
  • URLs added manually in the dashboard's Cache Manager.

The priority queue processes pages in the order they were requested, so urgent updates flow through before the normal queue's older-pages-first work.

 

The normal queue

The normal queue runs automatically and recaches pages that have passed their cache freshness threshold (the cache expiration you set under cache expiration). It starts with the oldest cached pages and works forward in time, so the snapshot most likely to be stale gets refreshed first.

 

How the daily recache rate is calculated

Your daily recache rate scales with how much you have cached and how often you want it refreshed:

NUM_CACHED_PAGES / CACHE_EXPIRATION (in days)

To get the per-hour rate, divide that result by 24. The more pages you cache, or the shorter your cache expiration (TTL), the higher the recache rate, up to your queue allocation.

💡 You can see the current speed of each queue under the Scheduled Rendering menu in your dashboard. To temporarily speed up the priority queue (for a launch, a sale, or a content migration), use the Change Recache Speed API with a urlsPerHour between 3,600 and 36,000 (or 0 for the automatic default).

When pages get removed from cache

If a cached page returns anything other than 200 OK or 304 Not Modified during recache, Prerender.io removes it from the cache. This keeps the cache clean and SEO-appropriate so AI crawlers and search engines never receive a broken or temporarily-redirected response.

The exact conditions that trigger removal are:

  • Status code < 200.
  • Status code > 200 and < 304 (covers most 2xx variants and all 3xx redirects up to 303).
  • Status code > 304 and < 500 (covers 305-307, 308, and all 4xx including 404 Not Found).
  • Three consecutive responses with status code ≥ 500 (single 5xx errors are tolerated as transient).

📝 If your source page returns a 301 or 302 redirect and you want Prerender.io to keep caching it (rather than remove it), use the prerender-status-code and prerender-header meta tags described in do 404 or 301 pages count toward my render counter. With those tags in place, Prerender.io returns the redirect to crawlers correctly without dropping the URL from cache.

Common pitfalls

  • Aggressive cache expiration multiplies recache work. Shorter TTLs mean higher recache frequency and higher render usage. Pick a cache expiration that matches how often your content actually changes.
  • Bloated sitemaps starve high-priority pages. If you list every URL in your sitemap, low-value pages compete with your most important ones for priority-queue capacity. Keep sitemap lists focused on pages that genuinely need fresh snapshots.
  • Unexpected 3xx or 4xx responses silently shrink your cache. A misconfigured redirect rule or a temporary 404 during a deployment can remove perfectly good URLs from cache. Test your routes after each deployment and check the status codes returned by Prerender.io to spot anything unexpected.

 

Get support

If your cache is shrinking unexpectedly, pages are not recaching at the rate you expect, or you want to confirm whether a specific URL is in the priority or normal queue:

To help us diagnose quickly, please include:

  • A few example URLs that aren't behaving as expected.
  • Your current cache expiration setting and total cached URL count.
  • The status code your origin returns for the affected URLs.
  • Whether you have recently changed your sitemap, cache expiration, or recache-speed API settings.

 

Related articles

💬 Still need help?
If your cache is shrinking unexpectedly or the recache rate isn't matching what the formula predicts, our support team can help dig into your account.
→ Contact us at support@prerender.io

 

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