interpreting ST03 Tasktype profile

Dear Gurus,

I am looking at causes of performance deterioration in SAP. I look at ST03 tasktype profile but there are some terms I do not quite understand the meaning. Pls can you throw some light.

1. DB Requests. what does this numner indicate? What is considered a DB request?

2. Buffer Calls. What buffer is it refering to? DB buffer? Which DB buffer then?

3. Physical DB Calls. What does this mean?

Thank you in advance.

Regards,

Mirella Russo