Measures of Query Cost(Cont.) For simplicity we just use the number of block transfers from disk and the number of seeks as the cost measures -time to transfer one block ts-time for one seek Cost for b block transfers plus S seeks b *t+S *ts We ignore CPU costs for simplicity Real systems do take CPU cost into account We do not include cost to writing output to disk in our cost formulae Database System Concepts-6th Edition 12.8 @Silberschatz,Korth and SudarshanDatabase System Concepts - 6 12.8 ©Silberschatz, Korth and Sudarshan th Edition Measures of Query Cost (Cont.) For simplicity we just use the number of block transfers from disk and the number of seeks as the cost measures tT – time to transfer one block tS – time for one seek Cost for b block transfers plus S seeks b * tT + S * tS We ignore CPU costs for simplicity Real systems do take CPU cost into account We do not include cost to writing output to disk in our cost formulae