CMPT 454 Lecture Notes - Lecture 1: Readwrite, Unique Key, Magnetic Storage
29 May 2016
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Document Summary
Index -> a structure that speeds up access to records based on some search criteria. B trees; hash tables; multi-dimensional indexes; bitmap indexes. Sql is a procedural query language, in the sense that it specifies the operation steps in order to get the result. Corollary: most queries have equivalent queries that use different operations but return the same result. Query optimization -> finding a good equivalent query if not the best. Size of intermediate relations -> every operation results in a table of determinable size, which subsequently affects later operations speed. A disk consists of platters that may be single or double sided (surfaces) Set of all tracks with the same diameter (throughout all surfaces) is called a cylinder. One head for each surface but only one head at a time may read/write. All heads are moved as a unit (disk head array) Therefore, all heads are in identical positions with respect to their surfaces (cylinder)
