ch12 - Database System Concepts, 5th Ed . Silberschatz,...

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Unformatted text preview: Database System Concepts, 5th Ed . Silberschatz, Korth and Sudarshan See www.db-book.com for conditions on re-use Chapter 12: Indexing and Hashing Chapter 12: Indexing and Hashing Silberschatz, Korth and Sudarshan 12.2 Database System Concepts - 5 th Edition, Oct 4, 2006 Chapter 12: Indexing and Hashing Chapter 12: Indexing and Hashing Basic Concepts Ordered Indices B +-Tree Index Files B-Tree Index Files Static Hashing Dynamic Hashing Comparison of Ordered Indexing and Hashing Index Definition in SQL Multiple-Key Access Silberschatz, Korth and Sudarshan 12.3 Database System Concepts - 5 th Edition, Oct 4, 2006 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 Silberschatz, Korth and Sudarshan 12.4 Database System Concepts - 5 th Edition, Oct 4, 2006 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 Silberschatz, Korth and Sudarshan 12.5 Database System Concepts - 5 th Edition, Oct 4, 2006 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. Silberschatz, Korth and Sudarshan 12.6 Database System Concepts - 5 th Edition, Oct 4, 2006 Dense Index Files Dense Index Files Dense index Index record appears for every search-key value in the file. Silberschatz, Korth and Sudarshan 12.7 Database System Concepts - 5 th Edition, Oct 4, 2006 Sparse Index Files Sparse Index Files Sparse Index : contains index records for only some search-key values....
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ch12 - Database System Concepts, 5th Ed . Silberschatz,...

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