And what are advantages and disadvantages of epidural and spinal?

Many. Spinal: fast onset, predictable onset, can be performed more easily and quickly. Disadvantages: 2% incidence of headache, nausea, labile blood pressure. Epidural: titratable dosing for controlled results, can be redosed if necessary, may be usable the day after surgery if desired for pain control. Dis: harder to place, may not work or provide full block, may also cause headach.
See below. A spinal has a predictable fast onset. Its disadvantages are a small chance of a headache and a drop in blood pressure. A epidural can be titrated to effect and redosed. It is a little harder to place.