Rate Limit Background Fetches

Note: Enabled by default, depends on statistics being enabled

To avoid overloading the origin server, PageSpeed will limit the number of background fetches it makes on a per-domain basis. As PageSpeed makes fetches it keeps a count of how many ongoing fetches there are for each domain, and if there are too many then additional fetches will only be allowed through if they're for user-facing requests. Other fetches (background fetches) will be queued up for completion later. If the queue gets too large, PageSpeed will give up on those background optimizations, leaving them to be reinitiated in response to a later request. This feature can be disabled by setting RateLimitBackgroundFetches to off:

pagespeed RateLimitBackgroundFetches off