Delay of pull through cache after upstream is updated

[originlake]

Hello,

We configured a ACR with pull through cache from docker hub, our production environment will pull the image with latest tag from time to time. The caching works fine, but the problem is, after we pushed the latest image to docker hub, if we pull the image from ACR immediately, it will still use the old cache. But if we wait for a couple minutes then pull the image, it can detect the changes and return the latest update.

Could you explain a bit what happens during the time? And what could be the maximum delay it could have so that we can be confident that the pulled image is in sync with upstream?