For example, lets say you were using storm to aggregate web visit start and end dates. A session starts with the first visit from a user and ends after 30 minutes of inactivity from that same user. This data is being streamed into storm in realtime as its collected. How would you tell storm to emit data after that 30 minutes of inactivity?
I am not sure but you can look for TOPOLOGY_TICK_TUPLE_FREQ_SECS properties in storm. As found in this article
Tick tuples: It’s common to require a bolt to “do something” at a fixed interval, like flush writes to a database. Many people have been using variants of a ClockSpout to send these ticks. The problem with a ClockSpout is that you can’t internalize the need for ticks within your bolt, so if you forget to set up your bolt correctly within your topology it won’t work correctly. 0.8.0 introduces a new “tick tuple” config that lets you specify the frequency at which you want to receive tick tuples via the “topology.tick.tuple.freq.secs” component-specific config, and then your bolt will receive a tuple from the __system component and __tick stream at that frequency.
You can also found the sample code to configure spouts or bolt to receive the tick tuple with a specific interval.