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From Amol Kekre <a...@datatorrent.com>
Subject Re: Modules
Date Tue, 03 Nov 2015 01:00:58 GMT
3,4 should follow conventions where the creator decides the api (including
accessibility). In general only those properties exposed by module creator
should be settable. What the module internally does with them is module
designer's call. Accessing internals of module from outside is uncommon.
For exampe in Java (or C++) private fields/members are not to be accessed.
Properties (setter and getter) are the api that module designer gives to
the module user. It is dangerous and has unintended consequences if module
user starts to access internals outside the api.

Partitioning should be next phase. As long as current design does not halt
partitioning it should be ok (which I believe is true).

Thks,
Amol


On Mon, Nov 2, 2015 at 3:44 PM, Vlad Rozov <v.rozov@datatorrent.com> wrote:

> 1. +1, though passing original DAG to module's populateDAG() it is not by
> design and is the current pull request implementation details.
>
> 2. While I agree that both Module and StreamingApplication let's
> module/application designer to expose DAG design reuse pattern and
> StreamingApplication interface may be extending Module, it does not seem to
> buy us much. Do we want to allow certain applications to be reused as
> Modules in other applications or should application package be different
> from Module package? The current approach is to distribute Modules as part
> of .jar for example as part of Malhar library without necessarily providing
> all necessary dependencies. Application package on other side must include
> all dependencies not provided by the platform.
>
> 3, 4. While this will help Module designer, it may complicate Module
> maintenance and how Modules are used. What if Module designer wants to
> change it's implementation and replace one operator implementation with
> another operator? Does StreamingApplication designer need to know internal
> structure of Modules? Should Module be considered as a black box during
> Application design time as it was initially planned?
>
> 5, 6, 7 +1. This is currently proposed behavior of Module functionality
> the way I understand it.
>
> 8. We need to see what Module designer can specify for partitioning. One
> of supported cases should be ability to specify cascading partitioning
> scheme.
>
> Thank you,
>
> Vlad
>
>
> On 11/2/15 10:30, Pramod Immaneni wrote:
>
>> I have some comments and suggestions on the module design. I think these
>> need to be taken into account before we can merge the implementation
>> provided below into the mainline code. I apologize if these should have
>> been brought up earlier as for some reason or the other I was out of loop
>> on this one
>>
>>      https://github.com/apache/incubator-apex-core/pull/148
>> <
>> https://github.com/apache/incubator-apex-core/pull/148#issuecomment-153104963
>> >
>>
>>      1. DAG scoping currently in the implementation is global for modules,
>> each module's populateDAG sees the entire DAG. It should be locally scoped
>> as one module does not and should not know about another.
>>      2. The module has a populateDAG method with exact same syntax as in
>> StreamingApplication. Is StreamingApplication also a module, should it
>> extend that interface.
>>      3. Setting properties for modules is too verbose. Module developer
>> needs to repeat every property they want exposed with a setter and getter
>> in JAVA. I don't disagree that module developer should be able to choose
>> which properties from which operators need to be exposed but the current
>> way seems to duplicate code. Here is a suggestion.
>>           a. Allow modules to specify which operators and properties can
>> be
>> accessible from outside. One way is in the "populateDAG" method of the
>> module when adding the operator have the ability to specify if this
>> operator can be accessible from outside and which or all properties can be
>> accessible.
>>           b. Provide methods in ModuleMeta or elsewhere to set property
>> values by specifying the operator name (friendly name) inside the module
>> and property name. If this is allowed by a. above it is successful else it
>> should fail.
>>           c. Allow a syntax in property files to specify the property in
>> b.
>> Example syntax dt.module.<modulename>.operator.<operatorname>.prop.<
>> propname>
>>      4. For attributes same mechanism as in 3 should apply for the
>> operators
>> that are exposed by the module.  For property file, example syntax
>> dt.module.<modulename>.operator.<operatorname>.attr.<attrname>
>>      5. Module developers in addition to 3. and 4. above may choose to
>> support module level properties and attributes. These should not be the
>> default when 3. and 4. are possible but complementary, in addition to
>> them.
>> In this case for properties they can implement setters and getters in the
>> module. For attributes the user should still be able to set the attributes
>> using the dag setAttribute method. You could introduce a method in the
>> module to process attributes that can get called by the engine once
>> everything is set.
>>      6. For 5. above setting global properties and attributes for module
>> is
>> akin to ideas that have been proposed for the application as well. A
>> consistent way must be possible for applications as well even if it is not
>> implemented now.
>>      7. For 5. or 6. above there should be a property file way of
>> specifying
>> the global module properties and attributes. Example syntax
>> dt.module.<modulename>.prop.<propname>,
>> dt.module.<modulename>.attr.<attrname>.
>> Notice the difference with 3. c. and 4 above that there is no operator
>> keyword here.
>>      8. Partitioning needs to be consistent with what the user will expect
>> when they see module as an entity. I will send an image of possible
>> examples of how the user will expect the physical plan to look in certain
>> cases.
>>
>> Thanks
>>
>>
>

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