MapDBCreator.java

public class MapDBCreator {

    public static void main(String[] args) {
        DB db = DBMaker.newFileDB("mapdbFile").transactionDisable().mmapFileEnablePartial().make();
        getEmployees().parallelStream().forEach(e -> createRecords(e, db));
    }

    private static List<Employee> getEmployees() {
    /* return employees list */
    }

    private static void createRecords(Employee employee, DB db) {
        JdbcTemplate template = /* spring JdbcTemplate creation */
                String query = "select name from sales where emp_id = " + employee.getId();
        final BTreeMap<String, Long> map = db.createTreeMap("Employee" + employee.getId())
                .nodeSize(32).comparator(String.CASE_INSENSITIVE_ORDER).make();
        template.query(query, rs -> {
            put(map, rs.getString("product_name"), rs.getLong("sales"));
        });
    }
}

This code is causing performance issues because of thread contention at MapDb threads are blocked at sun.nio.ch.FileChannelImpl#readInternal i Is there any better way to handle this?

Should I just go ahead with single file per map?