MVM GAE Compat -> Flex conversion Datastore w/ Objectify faster than g-c-j API's

[lesv]

Customer is doing a single read:

• Task: read 20,000+ entities
• Using Objectify on MVM-Java-Compat: 6 seconds to fetch (old api's)
• Using google-cloud-storage on Flex: 40 seconds to fetch

[yihanzhen]

This has been added to our feature backlog: https://github.com/GoogleCloudPlatform/google-cloud-java/wiki/Feature-backlog . This issue will be closed but is linked in the backlog and can continue to be used for comment and discussion.