conditional dataset output

[lars.bachmann]

Hi,

let's assume I have a dataset and depending on the input data and
different filter operations this dataset can be empty. Now I want to
output the dataset to HD, but I want that files are only created if the
dataset is not empty. If the dataset is empty I don't want any files.
The default way: dataset.write(...) will always create as many files as
the parallelism of this operator is configured - in case of an empty
dataset all files would be empty as well. I thought about doing
something like:

if (dataset.count() > 0) {
    dataset.write(...)
}

but I don't think thats the way to go, because dataset.count() triggers
a execution of the (sub)program.

Is there a simple way how to avoid creating empty files for empty
datasets?

Regards,

Lars

[Chesnay Schepler]

Hello Lars,

The only other way i can think of how this could be done is by wrapping
the used
outputformat in a custom format, which calls open on the wrapped
outputformat
when you receive the first record.

This should work but is quite hacky though as it interferes with the
format life-cycle.

Regards,
Chesnay

On 08.12.2016 16:39, [hidden email] wrote:

> Hi,
>
> let's assume I have a dataset and depending on the input data and
> different filter operations this dataset can be empty. Now I want to
> output the dataset to HD, but I want that files are only created if
> the dataset is not empty. If the dataset is empty I don't want any
> files. The default way: dataset.write(...) will always create as many
> files as the parallelism of this operator is configured - in case of
> an empty dataset all files would be empty as well. I thought about
> doing something like:
>
> if (dataset.count() > 0) {
>    dataset.write(...)
> }
>
> but I don't think thats the way to go, because dataset.count()
> triggers a execution of the (sub)program.
>
> Is there a simple way how to avoid creating empty files for empty
> datasets?
>
> Regards,
>
> Lars
>

[lars.bachmann]

Hi Chesnay,

I actually thought about the same but like you said it seems a bit hacky
;-). Anyway thank you!

Regards,

Lars

Am 08.12.2016 16:47 schrieb Chesnay Schepler:

> Hello Lars,
>
> The only other way i can think of how this could be done is by wrapping
> the used
> outputformat in a custom format, which calls open on the wrapped
> outputformat
> when you receive the first record.
>
> This should work but is quite hacky though as it interferes with the
> format life-cycle.
>
> Regards,
> Chesnay
>
> On 08.12.2016 16:39, [hidden email] wrote:
>> Hi,
>>
>> let's assume I have a dataset and depending on the input data and
>> different filter operations this dataset can be empty. Now I want to
>> output the dataset to HD, but I want that files are only created if
>> the dataset is not empty. If the dataset is empty I don't want any
>> files. The default way: dataset.write(...) will always create as many
>> files as the parallelism of this operator is configured - in case of
>> an empty dataset all files would be empty as well. I thought about
>> doing something like:
>>
>> if (dataset.count() > 0) {
>>    dataset.write(...)
>> }
>>
>> but I don't think thats the way to go, because dataset.count()
>> triggers a execution of the (sub)program.
>>
>> Is there a simple way how to avoid creating empty files for empty
>> datasets?
>>
>> Regards,
>>
>> Lars
>>