Shanthoosh Venkataraman created SAMZA-2118:
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Summary: Improve the shutdown sequence of AsyncRunLoop.
Key: SAMZA-2118
URL: https://issues.apache.org/jira/browse/SAMZA-2118
Project: Samza
Issue Type: Improvement
Reporter: Shanthoosh Venkataraman
Assignee: Shanthoosh Venkataraman
A samza container is comprised of multiple tasks and event-loop. Event loop is
the main orchestration layer between the different stages of a task(process,
commit, window) and delivers messages to task after polling from live
consumers.
Currently in samza, the event loop dispatches messages to the tasks as per
user-defined configuration `task.max.concurrency`. After dispatching messages
with count equal to `task.max.concurrency` to the tasks, the event loop is
blocked until the processing of at-least a single dispatched message
finishes(aka the task implementation invokes `taskCallBack.complete()` for
at-least a message).
When the event loop is blocked by this, the user thread would sometimes try to
shutdown the event loop. This shutdown intent marked by the user-thread will
take effect only when the processing of a single message completes. In
some-cases, when the task implementation does retry on failure for a message,
this could prolong the shutdown of the samza event loop.
This introduces tight coupling between the task processing time and the event
loop shutdown time. This behavior was observed predominantly in standalone
application where the samza container is shutdown as a part of the re-balancing
phase.
To alleviate this problem, as a part of this ticket, we propose to wake-up the
samza event-loop thread when the user-thread marks the intent to shutdown the
event-loop.
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