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Mul6agribute search keys should be considered when a

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Unformatted text preview:   For each update in the workload: –  –  Which agributes are involved in selec6on/join condi6ons? How selec6ve are these condi6ons likely to be? The type of update (INSERT/DELETE/UPDATE), and the agributes that are affected. Choice of Indexes •  What indexes should we create? –  Which rela6ons should have indexes? What field(s) should be the search key? Should we build several indexes? •  For each index, what kind of an index should it be? –  Clustered? Hash/tree? Choice of Indexes (Contd.) •  One approach: Consider the most important queries in turn. Consider the best plan using the current indexes, and see if a beger plan is possible with an addi6onal index. If so, create it. –  Obviously, this implies that we must understand how a DBMS evaluates queries and creates query evalua6on plans! –  For now, we discuss simple 1 ­table queries. •  Before crea6ng an index, must also consider the impact on updates in the workload! –  Trade ­off: Indexes can make queries go faster, updates slower. Require disk space, too. Index Selec6on Guidelines •  A...
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