Database index techniques.pdf

Database index techniques PDF

Source: Wikipedia. Pages: 28. Chapters: B-tree, Bitmap index, Compressed suffix array, Database index, Grid (spatial index), Incremental encoding, Indexed file, Inverted index, K-d tree, M-tree, Octree, Priority R-tree, Quadtree, R* tree, R+ tree, Reverse index, Substring index, UB-tree, X-tree, Z-order curve. Excerpt: In computer science, a B-tree is a tree data structure that keeps data sorted and allows searches, sequential access, insertions, and deletions in logarithmic time. The B-tree is a generalization of a binary search tree in that a node can have more than two children. (Comer 1979, p. 123) Unlike self-balancing binary search trees, the B-tree is optimized for systems that read and write large blocks of data. It is commonly used in databases and filesystems. A B-tree of order 2 (Bayer & McCreight 1972) or order 5 (Knuth 1998).In B-trees, internal (non-leaf) nodes can have a variable number of child nodes within some pre-defined range. When data are inserted or removed from a node, its number of child nodes changes. In order to maintain the pre-defined range, internal nodes may be joined or split. Because a range of child nodes is permitted, B-trees do not need re-balancing as frequently as other self-balancing search trees, but may waste some space, since nodes are not entirely full. The lower and upper bounds on the number of child nodes are typically fixed for a particular implementation. For example, in a 2-3 B-tree (often simply referred to as a 2-3 tree), each internal node may have only 2 or 3 child nodes. Each internal node of a B-tree will contain a number of keys. The keys act as separation values which divide its subtrees. For example, if an internal node has 3 child nodes (or subtrees) then it must have 2 keys: a1 and a2. All values in the leftmost subtree will be less than a1, all values in the middle subtree will be between a1 and a2, and all values in the rightmost subtree will be greater than a2. Usually, the number of keys is chosen to vary between and . In practice, the keys take up the most space in a node. The factor of 2 will guarantee that nodes can be split or combined. If an internal node has keys, then adding a key to that node can be accomplished by splitting the key node into two key nodes and adding the key to the parent node. Each split node

Top 10 performance tuning tips for relational databases Although newer relational databases and faster hardware run most SQL queries with a significantly small response time, there is always room for improvement. This paper lists 10 tips that every developer/DBA should consider when designing their database or writing SQL scripts. It also talks IDB - Index DataBase

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Database index techniques.pdf

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Sofia Voigt

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Using Indexes in Database Applications - Oracle Although the database creates an index for you on a column with a constraint, explicitly creating an index on such a column is recommended. You can use the following techniques to determine which columns are best candidates for indexing: Use the EXPLAIN PLAN feature to show a theoretical execution plan of a given query statement.