Outline ■Basic Concepts ■Ordered Indices B+-Tree Index Files ■B-Tree Index Files ■Hashing Write-optimized indices Spatio-Temporal Indexing Database System Concepts-7th Edition 14.2 ©Silberscha乜，Korth and Sudarshan
Database System Concepts - 7 14.2 ©Silberschatz, Korth and Sudarshan th Edition Outline ▪ Basic Concepts ▪ Ordered Indices ▪ B+ -Tree Index Files ▪ B-Tree Index Files ▪ Hashing ▪ Write-optimized indices ▪ Spatio-Temporal Indexing
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 indexentries)of the form search-key pointer 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”. Database System Concepts-7th Edition 14.3 ©Silberscha乜，Korth and Sudarshan
Database System Concepts - 7 14.3 ©Silberschatz, Korth and Sudarshan th Edition 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
Index Evaluation Metrics Access types supported efficiently.E.g., Records with a specified value in the attribute Records with an attribute value falling in a specified range of values. Access time ■Insertion time Deletion time ■Space overhead Database System Concepts-7th Edition 14.4 @Silberschatz,Korth and Sudarshan
Database System Concepts - 7 14.4 ©Silberschatz, Korth and Sudarshan th Edition Index Evaluation Metrics ▪ Access types supported efficiently. E.g., • Records with a specified value in the attribute • Records with an attribute value falling in a specified range of values. ▪ Access time ▪ Insertion time ▪ Deletion time ▪ Space overhead
Ordered Indices In an ordered index,index entries are stored sorted on the search key value. Clustering index:in a sequentially ordered file,the index whose search key specifies the sequential order of the file. Also called primary 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 nonclustering index. ■ Index-sequential file:sequential file ordered on a search key,with a clustering index on the search key. Database System Concepts-7th Edition 14.5 ©Silberscha乜，Korth and Sudarshan
Database System Concepts - 7 14.5 ©Silberschatz, Korth and Sudarshan th Edition Ordered Indices ▪ In an ordered index, index entries are stored sorted on the search key value. ▪ Clustering index: in a sequentially ordered file, the index whose search key specifies the sequential order of the file. • Also called primary 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 nonclustering index. ▪ Index-sequential file: sequential file ordered on a search key, with a clustering index on the search key
Dense Index Files Dense index-Index record appears for every search-key value in the file. E.g.index on ID attribute of instructorrelation 10101 10101 Srinivasan Comp.Sci. 65000 12121 12121 Wu Finance 90000 15151 15151 Mozart Music 40000 22222 22222 Einstein Physics 95000 32343 32343 El Said History 60000 33456 33456 Gold Physics 87000 45565 45565 Katz Comp.Sci. 75000 58583 58583 Califieri History 62000 76543 76543 Singh Finance 80000 76766 76766 Crick Biology 72000 83821 83821 Brandt Comp.Sci. 92000 98345 98345 Kim Elec.Eng. 80000 Database System Concepts-7th Edition 14.6 @Silberschatz,Korth and Sudarshan
Database System Concepts - 7 14.6 ©Silberschatz, Korth and Sudarshan th Edition 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