哪种数据类型和长度适合数据库中自动增量id的字段？

Let's say my website will be like Facebook which has a lot of entry everyday. So the entry for the field of auto increment id in database should be a lot lot lot. Instead of INT without specify the Length/Values, should I use BIGINT with 50 Length/Values for the id field? Let's say my website will be like Facebook whic