Extension:External Data/Throttling data retrievals

,,  ,  ,   and   can be throttled per data source, that is, a delay between calls to the same web service or program will be enforced. Meanwhile, a message informing that calls are throttled will be shown, or stale cache, if allowed and available will be used.

For web sites, soap services and server-side programs, throttling is configured by the settings  and  :
 * is a template generating a throttle key. Wildcards like,   or   (for web services) or   (for parameters to programs) will be replaced with their corresponding values. The default value is   meaning that, for example, any call to any page in Wikipedia in any language will have the throttle key  ;
 * is a float holding the mimimal interval, in seconds, between calls to web services or server-side programs with the same throttle key.

As with other settings, these are per data source, which can be:
 * The full URL,
 * host,
 * second-level domain,
 * for the default fallback for any site.

Throttling makes sense, when there are numerous calls of parser function (e.g., caused by a template embedded many times) addressing the same external service or program that either requires much computational resources or is, effectively, a call to an external service, like youtube-dl.

If there are no throttling key or throttling interval is zero or not set, there will be no throttling. This is the default setting.