ch11-indexing-hashing

ch11-indexing-hashing - Chapter 11: Indexing and Hashing...

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Chapter 11: Indexing and Hashing Chapter 11: Indexing and Hashing
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©Silberschatz, Korth and Sudarshan 11.2 Database System Concepts - 6 th Edition Chapter 12: Indexing and Hashing Chapter 12: Indexing and Hashing Basic Concepts Ordered Indices B + -Tree Index Files B-Tree Index Files -- skipping Static Hashing Dynamic Hashing -- skipping Comparison of Ordered Indexing and Hashing Index Definition in SQL Multiple-Key Access
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©Silberschatz, Korth and Sudarshan 11.3 Database System Concepts - 6 th Edition Basic Concepts Basic Concepts Indexing mechanisms used to speed up access to desired data. E.g., author catalog in library Search Key - attribute to set of attributes used to look up records in a file. An index file consists of records (called index entries ) of the form Index files are typically much smaller than the original file Two basic kinds of indices: Ordered indices: search keys are stored in sorted order Hash indices: search keys are distributed uniformly across “buckets” using a “hash function”. search-key pointer
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©Silberschatz, Korth and Sudarshan 11.4 Database System Concepts - 6 th Edition Index Evaluation Metrics Index Evaluation Metrics Access types supported efficiently. E.g., records with a specified value in the attribute or records with an attribute value falling in a specified range of values. Access time Insertion time Deletion time Space overhead
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©Silberschatz, Korth and Sudarshan 11.5 Database System Concepts - 6 th Edition Ordered Indices Ordered Indices In an ordered index , index entries are stored sorted on the search key value. E.g., author catalog in library. Primary index : in a sequentially ordered file, the index whose search key specifies the sequential order of the file. Also called clustering index The search key of a primary index is usually but not necessarily the primary key. Secondary index : an index whose search key specifies an order different from the sequential order of the file. Also called non-clustering index . Index-sequential file : ordered sequential file with a primary index.
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©Silberschatz, Korth and Sudarshan 11.6 Database System Concepts - 6 th Edition Dense Index Files Dense Index Files Dense index — Index record appears for every search-key value in the file. E.g. index on ID attribute of instructor relation
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©Silberschatz, Korth and Sudarshan 11.7 Database System Concepts - 6 th Edition Dense Index Files (Cont.) Dense Index Files (Cont.) Dense index on dept_name , with instructor file sorted on dept_name
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©Silberschatz, Korth and Sudarshan 11.8 Database System Concepts - 6 th Edition Sparse Index Files Sparse Index Files Sparse Index : contains index records for only some search-key values. Applicable when records are sequentially ordered on search-key
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ch11-indexing-hashing - Chapter 11: Indexing and Hashing...

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