Im creating a hibernate component to interact with large incoming data to persist, both save(create) and update data with volumes in the million of rows.

I am aware of the main differences around flush v commit, for example flush syncing the "dirty" data into the persistable underlying data, and that flush allows you to sync with the underlying persistable data without actually committing so that the transaction can be rolled back if required. Commit essentially commits all persistable data to the database.

Whats a reasonable size to do a batch insert? IS 50 the max amount for reasonable performance so something like:

for (i < 1000000)

if(i % 50 ) {
session.flush()
}

I gather 50 should match the value in the hibernate.jdbc.batch_size 50

yes 50 is reasonable to start from, you can experiment with slightly higher or lower (100, 20) to see how performance is affected as it depends on your hardware, connectivity, database configuration and data sizes: hard to predict.

Make sure you also use session.clear(): flush won't remove existing (flushed) entities from the session, so you would run out of memory otherwise.

Ok thank you for that.
I gather hibernate just batches up the inserts rather than one big insert with all the relevant data? Is it possible to use the oracle drivers to translate those individual inserts into one big insert with all the data? Something like you can do in MySQL?