It is not about a use case difference. My proposal and APEXCORE-408
address the same use case - how to re-allocate resources for batch
applications or applications where processing happens in stages. The
difference between APEXCORE-408 and the proposal is shift in complexity
from application logic to the platform. IMO, supporting batch
applications using APEXCORE-408 will require more coding on the
application side.
Thank you,
Vlad
On 4/5/17 21:57, Thomas Weise wrote:
I think this needs more input on a use case level. The ability to
dynamically alter the DAG internally will also address the resource
allocation for operators:
https://issues.apache.org/jira/browse/APEXCORE-408
It can be used to implement stages of a batch pipeline and is very flexible
in general. Considering the likely implementation complexity for the
proposed feature I would like to understand what benefits it provides to
the user (use cases that cannot be addressed otherwise)?
Thanks,
Thomas
On Sat, Apr 1, 2017 at 12:23 PM, Vlad Rozov <v.ro...@datatorrent.com> wrote:
Correct, a statefull downstream operator can only be undeployed at a
checkpoint window after it consumes all data emitted by upstream operator
on the closed port.
It will be necessary to distinguish between closed port and inactive
stream. After port is closed, stream may still be active and after port is
open, stream may still be inactive (not yet ready).
The more contributors participate in the discussion and implementation,
the more solid the feature will be.
Thank you,
Vlad
Отправлено с iPhone
On Apr 1, 2017, at 11:03, Pramod Immaneni <pra...@datatorrent.com>
wrote:
Generally a good idea. Care should be taken around fault tolerance and
idempotency. Close stream would need to stop accepting new data but still
can't actually close all the streams and un-deploy operators till
committed. Idempotency might require the close stream to take effect at
the
end of the window. What would it then mean for re-opening streams within
a
window? Also, looks like a larger undertaking, as Ram suggested would be
good to understand the use cases and I also suggest that multiple folks
participate in the implementation effort to ensure that we are able to
address all the scenarios and minimize chances of regression in existing
behavior.
Thanks
On Sat, Apr 1, 2017 at 8:12 AM, Vlad Rozov <v.ro...@datatorrent.com>
wrote:
All,
Currently Apex assumes that an operator can emit on any defined output
port and all streams defined by a DAG are active. I'd like to propose an
ability for an operator to open and close output ports. By default all
ports defined by an operator will be open. In the case an operator for
any
reason decides that it will not emit tuples on the output port, it may
close it. This will make the stream inactive and the application master
may
undeploy the downstream (for that input stream) operators. If this
leads to
containers that don't have any active operators, those containers may be
undeployed as well leading to better cluster resource utilization and
better Apex elasticity. Later, the operator may be in a state where it
needs to emit tuples on the closed port. In this case, it needs to
re-open
the port and wait till the stream becomes active again before emitting
tuples on that port. Making inactive stream active again, requires the
application master to re-allocate containers and re-deploy the
downstream
operators.
It should be also possible for an application designer to mark streams
as
inactive when an application starts. This will allow the application
master
avoid reserving all containers when the application starts. Later, the
port
can be open and inactive stream become active.
Thank you,
Vlad
