If one or more downstream subscribers to a track are not paused, the relay MUST have an unpaused upstream subscription, in order to receive and forward the requested Objects. When all downstream subscribers are paused, the relay chooses whether to pause upstream at its discretion, considering the following tradeoffs and deployment considerations:
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Leaving the upstream subscription unpaused starts object delivery and pre-warms the relay's cache, so objects are available when a downstream subscriber resumes. This reduces latency but consumes upstream and publisher resources for content no downstream subscriber is currently receiving.
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Pausing the upstream subscription avoids that work, at the cost of higher latency when delivery is later resumed.