Lecture 07 - Physical Design.pdf

Three types 1 key range paroning 2 hash paroning or 3

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Three types : (1) Key Range [email protected]@oning, (2) Hash [email protected]@oning, or (3) Composite [email protected]@oning. § Ver8cal Par88oning : [email protected] the columns of a logical [email protected] into several separate physical tables: Useful for [email protected] where different users need access to different columns. The primary key must be repeated in each file. § Combina8ons of Horizontal and [email protected] Lee-758Y-05 19
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[email protected]@oning Pros and Cons § Advantages of [email protected]@oning: Efficiency : Records used together are grouped together. Local op8miza8on : Each [email protected]@on can be [email protected] for performance. Security : data not relevant to users are segregated. Recovery and up8me : smaller files take less @me to back up. Load balancing : [email protected]@ons stored on different disks, reduces [email protected] § Disadvantages of [email protected]@oning: Inconsistent access speed : Slow retrievals across [email protected]@ons. Complexity : Non-transparent [email protected]@oning. Extra space or update 8me : Duplicate data; access from [email protected] [email protected]@ons. Lee-758Y-05 20
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Rules for Using Indexes § Use on larger tables. § Index the primary key of each table. § Index search fields (fields frequently in WHERE clause). § Fields in SQL ORDER BY and GROUP BY commands. § When there are >100 values but not when there are <30 values. § DBMS may have limit on number of indexes per table and number of bytes per indexed field(s). § Be careful of indexing aGributes with null values; many DBMSs will not recognize null values in an index search. Lee-758Y-05 21
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  • Fall '18
  • AdamLee
  • Data Management, Relational model, Database management system

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