Real-time intermediate persistence explanation

Could you please explain in more details the real-time intermediate persistence?
How it it related to the windowPeriod?
How it behaves in case of real-time restart?
What if after restart there are persisted messaged that are out of windowPeriod?
How it’s related to kafka offsets? “2016-01-05T20:25:20,423 INFO [impressions_test4-incremental-persist] io.druid.firehose.kafka.KafkaEightFirehoseFactory - committing offsets”

I would like to know all these in order to know what to expect from real-time in different situations. What if i restart the node? What will happen with data if i have two real-time nodes and restart one of them?

Thanks, Vadim.

Hi Vadim, have you tried this http://static.druid.io/docs/druid.pdf?