1. A method, comprising: receiving a data stream for an application running on a distributed streaming platform over a networked cluster of servers; converting the data into a plurality of data tuples structured according to a schema; repeatedly emitting a specified number of the data tuples as a streaming window, which is separated from other streaming windows by a leading control tuple associated with an ordinal identifier for the streaming window and by a trailing control tuple associated with the same ordinal identifier, wherein the streaming window is an atomic sequence of tuples that is associated with a recovery policy; and emitting a checkpointing tuple following the trailing control tuple after a specified number of streaming windows, wherein the checkpointing tuple causes checkpointing of an instance of an operator for the application when the checkpointing tuple is received by the instance, wherein each of the operations is executed by one or more processors in real time or near real time rather than offline.