Re: open/close ports and active/inactive streams

[Vlad Rozov]

It is exactly the same use case with the exception that it is not 
necessary to write data to files. Consider 3 operators, an input 
operator, an aggregate operator and an output operator. When the 
application starts, the output port of the aggregate operator should be 
in the closed state, the stream between the second and the third would 
be inactive and the output operator does not need to be allocated. After 
the input operator process all data, it can close the output port and 
the input operator may be de-allocated. Once the aggregator receives EOS 
on it's input port, it should open the output port and start writing to 
it. At this point, the output operator needs to be deployed and the 
stream between the last two operators (aggregator and output) becomes 
active.

In a real batch use case, it is preferable to have full application DAG 
to be statically defined and delegate to platform 
activation/de-activation of stages. It is also preferable not to write 
intermediate files to disk/HDFS, but instead pass data in-memory.

Thank you,

Vlad

On 4/6/17 09:37, Thomas Weise wrote:
You would need to provide more specifics of the use case you are thinking
to address to make this a meaningful discussion.

An example for APEXCORE-408 (based on real batch use case): I have two
stages, first stage produces a set of files that second stage needs as
input. Stage 1 operators to be released and stage 2 operators deployed when
stage 2 starts. These can be independent operators, they don't need to be
connected through a stream.

Thomas


On Thu, Apr 6, 2017 at 9:21 AM, Vlad Rozov <v.ro...@datatorrent.com> wrote:

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