Help Needed for APEXCORE-619 Issue : When application is relaunched after long time with stateless opeartors at the end of the DAG, the stateless operators starts with a very high windowId. In this case the stateless operator ignors all the data received till upstream operator catches up with it. This breaks the *at-least-once* gaurantee while relaunch of the opeartor or when master is killed and application is restarted.
Solutions: - Fix windowId for stateless leaf operators from upstream opeartor. But it has some issues when we have a join with two upstrams operators at different windowId. If we set the windowID to min(upstream windowId), then we need to again recalulate the new recovery window ids for upstream paths from this operators. - Other solution is to create a empty file in checkpoint directory for stateless operators. This will help us to identify the checkpoints of stateless operators during relaunch instead of computing from latest timestamp. - Bring the entire DAG to committedWindowId. This could be achived using writing committedWindowId in a journal. we need to make sure that we are not puring the checkpointed state until the committedWundowId is saved in journal. Let me know your thoughs on this and preferred solution. Regards, -Tushar.
