BigQuery IO Source is not Exporting to GCS as written in documentation

[kennknowles]

Did some check on the beam code and find out that DataFlow is querying BigQuery and retrieve the result using pagination [1]. As per our understanding, this means no parallelism on reading BigQuery table. It is contradictory to what the documentation is telling us [2].
 
Is this some kind of work in progress? I'm filing as a bug since documentation telling me that it is using GCS meanwhile it's using NativeSourceReader which yield data per row as iterator.
 
[1] 

beam/sdks/python/apache_beam/io/gcp/bigquery.py

Line 1083 in 520b3a2

while True:

[2] 

beam/sdks/python/apache_beam/io/gcp/bigquery.py

Line 60 in 520b3a2

The main and side inputs are implemented differently. Reading a BigQuery table

Imported from Jira BEAM-5352. Original Jira may contain additional context.
Reported by: rendybjunior.

[rendybjunior]

Thanks for migrating the issue.