Primary and Secondary Indices Indices offer substantial benefits when searching for records. BUT:Updating indices imposes overhead on database modification--when a file is modified,every index on the file must be updated, Sequential scan using primary index is efficient,but a sequential scan using a secondary index is expensive Each record access may fetch a new block from disk Block fetch requires about 5 to 10 milliseconds,versus about 100 nanoseconds for memory access Database System Concepts-6th Edition 11.11 @Silberschatz,Korth and SudarshanDatabase System Concepts - 6 11.11 ©Silberschatz, Korth and Sudarshan th Edition Primary and Secondary Indices Indices offer substantial benefits when searching for records. BUT: Updating indices imposes overhead on database modification --when a file is modified, every index on the file must be updated, Sequential scan using primary index is efficient, but a sequential scan using a secondary index is expensive Each record access may fetch a new block from disk Block fetch requires about 5 to 10 milliseconds, versus about 100 nanoseconds for memory access