Matthew Stowe created AVRO-2098:
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Summary: Avro OCF support for non-seekable stream.
Key: AVRO-2098
URL: https://issues.apache.org/jira/browse/AVRO-2098
Project: Avro
Issue Type: New Feature
Components: csharp
Affects Versions: 1.8.2
Environment: csharp
Azure Data Lake Analytics
Reporter: Matthew Stowe
Priority: Minor
The Microsoft Azure environment supports saving Apache Avro files from an Event
Hub via a feature called Event Hub Capture. The Event Hub Capture feature can
be configured to Azure Data Lake Storage (ADLS).
When saving files to ADLS it is common to use Azure Data Lake Analytics (ADLA)
to run batch processing jobs in U-SQL over the raw storage files. When doing
this ADLA supports extractors that can deal with the format of the file (e.g.
Avro OCF) and extract file contents for downstream manipulation and filtering.
An issue I have encountered with the existing csharp implementation is that the
DataFileReader relies on the provided stream to support seeking. However, the
stream provided by ADLA does not support seeking. This leaves the integrating
developer with 2 options...
1 is to read the entire stream in to memory and provide a memory backed stream
to the DataFileReader. This is not ideal as files can be large and consuming a
lot of memory at once during processing may have undesired affects on ADLA's
ability to process files in parallel, as resources are of course limited.
2 is to enhance the DataFileReader to be able to work with streams that are not
seekable. With respect to this option I have implemented a short-term
workaround that can wrap a non-seekeable stream and allow seeking in the
pattern employed by the DataFileReader until this feature has been reviewed and
potentially implemented. My workaround is brittle and subject to breaking as
the DataFileReader evolves and is not the desired long term approach to dealing
with this issue.
[AvroDataFileReaderStream.cs|https://github.com/thebothead/apache-avro-adla/blob/master/src/Avro.IO.ADLA/AvroDataFileReaderStream.cs]
Cheers,
Matt
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