Joshua Fox commented on BEAM-991:

Daniel Halperin, unfortunately I cannot participate too much in the development 
and full testing, both for the usual  reason of time commitments but also 
because I am not close enough to the infrastructure to fully understand what is 
happening, particularly in edge cases. However, I will be glad to serve as an 
early user.

My situation: I wrote a Datastore backup in Dataflow, after Google's Backup and 
Managed Backup tool failed on various bugs.

However, this new tool cannot copy any Kind with Item size >20 KB (max in 
Datastore is 1 MB). So, I can only use it to backup Kinds with average Item 
size 10 KB (since there may be variation.) I wrote a second a simple 
multithreaded but nondistributed backup tool, using  "select-insert"  loops. It 
works, but of course is less scalable and more expensive than the Dataflow 
tool. I use a combination of the Dataflow and the nondistributed tool now, for 
different Kinds, but can easily switch to using just Dataflow.

> DatastoreIO Write should flush early for large batches
> ------------------------------------------------------
>                 Key: BEAM-991
>                 URL: https://issues.apache.org/jira/browse/BEAM-991
>             Project: Beam
>          Issue Type: Bug
>          Components: sdk-java-gcp
>            Reporter: Vikas Kedigehalli
>            Assignee: Vikas Kedigehalli
> If entities are large (avg size > 20KB) then the a single batched write (500 
> entities) would exceed the Datastore size limit of a single request (10MB) 
> from https://cloud.google.com/datastore/docs/concepts/limits.
> First reported in: 
> http://stackoverflow.com/questions/40156400/why-does-dataflow-erratically-fail-in-datastore-access

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