Session10

Session10 - Chapter 12: Indexing and Hashing Basic Concepts...

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Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke 1 Chapter 12: Indexing and Hashing Chapter 12: Indexing and Hashing x Basic Concepts x Ordered Indices x B+-Tree Index Files x B-Tree Index Files x Static Hashing x Dynamic Hashing x Comparison of Ordered Indexing and Hashing x Index Definition in SQL x Multiple-Key Access
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Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke 2 Basic Concepts Basic Concepts x Indexing mechanisms used to speed up access to desired data. s E.g., author catalog in library x Search Key - attribute or set of attributes used to look up records in a file. x An index file consists of records (called index entries ) of the form x Index files are typically much smaller than the original file x Two basic kinds of indices : s Ordered indices: search keys are stored in sorted order s Hash indices: search keys are distributed uniformly across “buckets” using a “hash function”. search-key pointer
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Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke 3 Index Evaluation Metrics Index Evaluation Metrics x Access types supported efficiently. E.g., s records with a specified value in the attribute s or records with an attribute value falling in a specified range of values. x Access time x Insertion time x Deletion time x Space overhead Indexing techniques evaluated on basis of:
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Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke 4 Ordered Indices Ordered Indices x In an ordered index , index entries are stored sorted on the search key value. E.g., author catalog in library. x Primary index : in a sequentially ordered file, the index whose search key specifies the sequential order of the file. s Also called clustering index /* Not! */ s The search key of a primary index is usually but not necessarily the primary key. x Secondary index : an index whose search key specifies an order different from the sequential order of the file. Also called non-clustering index . /* Wrong Again! */ x Index-sequential file : ordered sequential file with a primary index.
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Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke 5 Dense Index Files Dense Index Files x Dense index — Index record appears for every search-key value in the file.
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Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke 6 Sparse Index Files Sparse Index Files x Sparse Index : contains index records for only some search-key values. s
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Session10 - Chapter 12: Indexing and Hashing Basic Concepts...

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