[STORM-1351] Storm spouts and bolts need a way to communicate problems back to toplogy runner

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Component/s: storm-core
• Assignee: Roshan Naik
• Reporter: Roshan Naik
• Created: 24/Nov/15 23:06
• Updated: 03/Dec/15 03:41

Description

A spout can be having a problem generating a tuple in nextTuple() because
-a) there is no data to generate currently

• b) there is some I/O issues it is experiencing

If the spout returns immediately from the nextTuple() call then the nextTuple() will be invoked immediately leading to CPU spike. The CPU spike would last till the situation is remedied by new coming data or the i/o issues getting resolved.

Currently to work around this, the spouts will have to implement a exponential backoff mechanism internally. There are two problems with this:

• each spout needs to implement this backoff logic
• since nextTuple() has an internal sleep and takes longer to return, the latency metrics computation gets thrown off

Thoughts for Solution:
The spout should be able to indicate a 'no data', 'experiencing error' or 'all good' status back to the caller of nextTuple() so that the right backoff logic can kick in.

• The most natural way to do this is using the return type of the nextTuple method. Currently nextTuple() returns void. However, this will break source and binary compat since the new storm will not be able to invoke the methods on the unmodified spouts. This breaking change can only be considered as an option only prior to v1.0.

• Alternatively this can be done by providing an additional method on the collector to indicate the condition to the topology runner. The spout can invoke this explicitly. the metrics can then also account for 'no data' and 'error attempts'

• Alternatively - The toplogy runner may just examine the collector if there was new data generated by the nextTuple() call. In this case it cannot distinguish between errors v/s no incoming data.