Operations to Consider Scan: fetch all records in a certain relation. Search with equality selection: find all the tuples with age=5 Search range selection: find all tuples with age between 5 and 50 Insert: put a new record into the file. Delete: a record from the file.

Costs to Measure B data pages, R records per page. Average time to read or write a disk page: D (typically 15msec) Average time to process a record: C (typically 1 to 10 microsec) Time to apply hash function: H (typically 1 to 10 microsec) So, we count mostly I/O costs.

Indexes Auxiliary structure that speeds up operations that are not supported by the basic file organization. Formally: a set of data entries with an efficient way of locating all the entries with search key k. Questions: how are the data entries organized to support the efficient access? What is a data entry exactly? Options for data entry: 1. An actual data record (whose value is k) 2. A pair (k, rid) - pointer to the real record. 3. A pair (k, list-of-rid)

Properties of Indexes - clustered vs. unclustered (how many clustered indexes can we have on a file?) - Dense vs. sparse indexes - Primary and secondary indexes (is the key entry a superkey?)

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