|Yes NTP can still have skew. It may be measured in fractions of a second, but with Flink that can be significant if you care about sub-second latency accuracy. Since I have a 20 stage stream with 0.002 second latency it can matter.|
Back pressure is the limiting of input due to the inability of down-stream tasks to accept input. For example if you have a map that reads from a database to enhance an element, that may limit earlier steps performance as they can not push elements to it faster than it can read from the database. This can flow all the way back to the source and slow records coming into the system.