Also defines the granulity of the reported progression.
TODO Also honor this limit in load.
	# The maximum number of entities saved in one request.
	#
	# Also defines the granulity of the reported progression.
	#
	# TODO Also honor this limit in `load`.
	var batch_max_size = 512 is writable
					lib/neo4j/graph/graph.nit:187,2--192,37