Some information on performance when using the DataStore back end in Database abstraction with google apps script
The library reference is 


Comparing scriptDB, parse and datastore

In Migrate data from scriptDb to Datastore I showed how to copy over data easily from scriptdb to datastore. The good thing about abstracting the database is that code is the same regardless of which database use you are using (once you’ve got the handle). 
In this example I’m copying 1000 records from scriptDB to each of, datastore and Note that each of these drivers using batching, so it’s a fair enough comparison. For the purposes of the test, I’ve switched caching off in all cases. There are 3 operations performed – deleting 1000 records, adding 1000 records and querying them.
Note: since doing this test, I’ve improved batching on deletion – see Comparing all back ends performance for the improved performance numbers.

Here’s the code



Although DataStore is quicker at deletion, using its JSON API makes it slower than Parse for both querying and writing. Unless you are planning to use DataStore for its extensive capabilities and scalability outside the simple scope of being a replacement for ScriptDB, it’s hard to see why you wouldn’t choose and avoid all those quota problems

See more like this in Database abstraction with google apps script and Datastore driver and for all back end performance see Comparing all back ends performance