"Pending request latency arises when all of your application's available instances are too busy to serve new requests. When this happens, incoming requests go t

"Pending request latency arises when all of your application's available instances are too busy to serve new requests. When this happens, incoming requests go to a pending request queue." https://developers.google.com/appengine/docs/adminconsole/performancesettings#scheduler https://developers.google.com/appengine/docs/adminconsole/pe... Pending latency is exposed as a metric on the App Engine Dashboard.