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Query Processing, optimization, and indexing techniquesWhat’s this tutorial about? From here:SELECT C.name AS Course, count(S.students) AS CntFROM courses C, subscription SWHEREC.lecturer = “Calders”AND C.courseID = S.courseID To there:Course Cnt“Advanced Databases” 67“Data mining en kennissystemen” 19 What’s in between? How does a relational DBMS get there efficiently.thBased upon slides for: Database System Concepts - 5 Edition, Aug 27, 2005.1Physical Reality Cost of query evaluation is generally measured as total elapsed time for answering query Many factors contribute to time cost disk accesses, CPU, or even network communication Typically disk access is the predominant cost, and is also relatively easy to estimate. Measured by taking into account Number of seeks * average-seek-cost Number of blocks read * average-block-read-cost Number of blocks written * average-block-write-cost Cost to write a block is greater than cost to read a block – data is read back after being written to ensure that the write was successfulthBased upon slides for: Database System Concepts - 5 Edition, Aug 27, 2005.What’s this tutorial about? Factors that influence the efficiency: How is the data stored? Primary and secondary indices B-trees Composite search keys Hashing How is the query processed? Relational algebra Query evaluation plan We start with the second part …thBased upon slides for: Database System ...