Tuning the Database Design (Cont.) Materialized Views Materialized views can help speed up certain queries Particularly aggregate queries ■Overheads ·Space Time for view maintenance Immediate view maintenance:done as part of update txn time overhead paid by update transaction Deferred view maintenance:done only when required update transaction is not affected,but system time is spent on view maintenance until updated,the view may be out-of-date Preferable to denormalized schema since view maintenance is systems responsibility,not programmers Avoids inconsistencies caused by errors in update programs Database System Concepts-7th Edition 25.6 ©Silberscha乜，Korth and SudarshanDatabase System Concepts - 7 25.6 ©Silberschatz, Korth and Sudarshan th Edition Tuning the Database Design (Cont.) Materialized Views ▪ Materialized views can help speed up certain queries • Particularly aggregate queries ▪ Overheads • Space • Time for view maintenance ▪ Immediate view maintenance: done as part of update txn • time overhead paid by update transaction ▪ Deferred view maintenance: done only when required • update transaction is not affected, but system time is spent on view maintenance ▪ until updated, the view may be out-of-date ▪ Preferable to denormalized schema since view maintenance is systems responsibility, not programmers • Avoids inconsistencies caused by errors in update programs