SpannerIO.read() parallelism limited by partition count #20767
Description
Setting the partition size / count is not possible:
Note: This hint is currently ignored by sessions.partitionQuery and sessions.partitionRead requests.
https://cloud.google.com/spanner/docs/reference/rest/v1/PartitionOptions
Adding a Reshuffle might be the only choice, but it adds time and resource usage.
cc: [~chamikara][~nielm]
Imported from Jira BEAM-11722. Original Jira may contain additional context.
Reported by: udim.