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https://issues.apache.org/jira/browse/ARROW-15969?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17511724#comment-17511724
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Alessandro Molina edited comment on ARROW-15969 at 3/24/22, 9:31 AM:
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{quote}Imho due to this difference, implementing RBR on the file reader would
lead to 'awkwardness' down the road - what if user wants to consume contents of
the file using RBR multiple times?
{quote}
I wasn't suggesting that {{RecordBatchReader}} should be implemented on top of
{{{}RecordBatchFileReader{}}}, I was mostly wondering if it wasn't the case for
the opposite. A random access reader should be able to reproduce all the
features of a stream reader, plus some additional capabilities like seeking.
The reason I was wondering is that if we exposed a class hierarchy like
{code:java}
RecordBatchReader
/. \
/ \
RecordBatchStreamReader RecordBatchFileReader{code}
We wouldn't have to deal with "converting" file readers, they could be used
directly wherever a \{{RecordBatchReader}} was needed
In the end, I don't see a reason why {{RecordBatchFileReader}} can't have a
{{get_next_batch}} method, when reading a file you have a current position for
the current ongoing read.
was (Author: amol-):
{quote}Imho due to this difference, implementing RBR on the file reader would
lead to 'awkwardness' down the road - what if user wants to consume contents of
the file using RBR multiple times?
{quote}
I wasn't suggesting that {{RecordBatchReader}} should be implemented on top of
{{{}RecordBatchFileReader{}}}, I was mostly wondering if it wasn't the case for
the opposite. A random access reader should be able to reproduce all the
features of a stream reader, plus some additional capabilities like seeking.
The reason I was wondering is that if we exposed a class hierarchy like
{code:java}
RecordBatchReader
/. \
/ \
RecordBatchStreamReader RecordBatchFileReader{code}
We wouldn't have to deal with "converting" file readers, they could be used
directly wherever a {{RecordBatchReader }}was needed
In the end, I don't see a reason why {{RecordBatchFileReader}} can't have a
{{get_next_batch}} method, when reading a file you have a current position for
the current ongoing read.
> [C++][Python] Add conversion from RecordBatchFileReader to RecordBatchReader
> ----------------------------------------------------------------------------
>
> Key: ARROW-15969
> URL: https://issues.apache.org/jira/browse/ARROW-15969
> Project: Apache Arrow
> Issue Type: Improvement
> Components: C++, Python
> Reporter: Lubo Slivka
> Priority: Major
>
> The suggested improvement is to introduce a conversion/adapter so that all
> batches from RecordBatchFileReader can be read one-by-one using
> RecordBatchReader.
> Perhaps a new instance method RecordBatchFileReader.to_reader()? This would
> follow the suit of for instance the pyarrow.flight.MetadataRecordBatchReader
> which also has to_reader().
> *Motivation*
> Record Batches serialized into IPC file format can be read using
> RecordBatchFileReader. The interface of this reader is incompatible with
> RecordBatchReader.
> This impacts for instance the Flight RPC DoGet, where it is not possible to
> efficiently (e.g. fully in C++) send out all data by using
> pyarrow.flight.RecordBatchStream. However, there may be other use cases where
> client code wants to read data batch-by-batch transparently, without caring
> about the serialization format.
> Further background is here:
> [https://lists.apache.org/thread/b9jwk103fgxfo4kct12t00ymdft7bklb]
>
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