Godeps/_workspace/src/gopkg.in/mgo.v2/session.go
func (p *Pipe) Batch(n int) *Pipe {
	p.batchSize = n
	return p
}
func (p *Pipe) Batch(n int) *Pipe {
	p.batchSize = n
	return p
}
// Batch sets the batch size used when fetching documents from the database.
// It's possible to change this setting on a per-session basis as well, using
// the Batch method of Session.
//
// The default batch size is defined by the database server.