7 - Indexing Structures for Files (Lecture Session-7)...

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Indexing Structures for Files (Lecture Session-7) Chapter 14 Thu, Feb 04, 2010 1 DLPD, BITS-Pilani. Prepared by Dr.R. Gururaj, Asst.Professor of CS
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Thu, Feb 04, 2010 DLPD, BITS-Pilani. Prepared by Dr.R. Gururaj, Asst.Professor of CS 2 •Introduction to Indexing •Search keys •Multilevel indexing •B+ tree Indexing Contents
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Thu, Feb 04, 2010 DLPD, BITS-Pilani. Prepared by Dr.R. Gururaj, Asst.Professor of CS 3 Disk Storage Devices An index for a file works in much the same way as a catalog in a library. In a library cards are kept in alphabetical order. So we don’t have to search all cards. In real world databases, indexes may be too large to be handled efficiently. Hence some sophisticated techniques are to be used. Techniques for efficient retrieval of required records from disk. Hashing Indexing
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Thu, Feb 04, 2010 DLPD, BITS-Pilani. Prepared by Dr.R. Gururaj, Asst.Professor of CS 4 The criteria for evaluating the hashing or indexing techniques Access time Insertion time (new indexes or new records) Deletion time space overhead Some times more than one indexing may be required for a file. The attribute or the set of attributes used for look up records in a file is called a ‘ search key . It is different from usual meaning of key in relational database.
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DLPD, BITS-Pilani. Prepared by Dr.R. Gururaj, Asst.Professor of CS 5 The index whose search key specifies the sequential order of the file is the primary index . The other indexes are called ‘ secondary indexes . The search key of a primary index is usually the primary key. A sequentially ordered file together with a primary index are called index– sequential file . Index record: Like data records, index records are also stored in database. Any index record normally has two fields
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7 - Indexing Structures for Files (Lecture Session-7)...

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