a. In an _____ scan, the optimizer determines it is efficient to use the index s
ID: 3814316 • Letter: A
Question
a. In an _____ scan, the optimizer determines it is efficient to use the index structure to retrieve multiple rows required by the query. b. A Bitmap index is composed of several strings of _____ each of them could be _____ or _____. c. What is the difference between an index and a key? d. Describe 2 examples of where the optimizer decides to do a full table scan even if a table has an index: e. The two main costs that contribute to query optimization are _____ and _____. f. Pick True or False The cost of processing a query is dominated by secondary storage access compared to memory access _____ g. Pick True or False A systematic query optimization is used for estimation of the cost of different execution strategies and choosing the execution plan with the lowest cost estimate _____ h. What is pipelining and how is it used in query optimization _____ i. Which of the following will provide an efficient execution strategy? 1. Delaying the join operation till the end 2. Performing Project operation last 3. Performing select operation as early as possible 4. All the aboveExplanation / Answer
a. In Index scan scan, the optimizer determines it is efficient to use the index structure to retrieve multiple rows
required for the query.
b. a bitmap index is composed of several strings of bits each of them could be on or off.
c. Index:An index is a structure that RDBMS(database management system) provides to improve data processing. An index has nothing to do with a logical database structure.
Keys : Keys are special fields that play very specific roles within a table, and the type of key determines its purpose within the table.
Difference: Keys are logical structures you use to identify records within a table and indexes are physical structures you use to optimize data processing.
d. 1.If the rows are in a different order in the two tables then the indexes in the two systems can have different clustering factors, and hence difference estimated costs for index access. In this cases full table scan is performed. 2.you may have different setting for OPTIMIZER_MODE - make sure it's not on RBO.
e. the two main costs that contibute to query optimization are run time cost and execution cost.
f. TRUE The cost of processing a query is usually dominated by secondary secondary storage access, which is slow compared to memory access
g. TRUE. A systematic query optimization is used for estimation of the cost of different execution strategies and choosing theexecution plan with the lowest cost estimate.
h. Pipelining is an implementation technique where multiple instructions are overlapped in execution. With pipelining, the results of an operator are passed along as input to the next operator, before the first operator completes its execution, thus ennhances query optimization.
i. Option 4. All the given options provide an efficient execution strategy.
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