Data Indexing: Understanding Tree-based and Hash-based Indexes - Prof. Yicheng Tu, Study notes of Deductive Database Systems

Download Data Indexing: Understanding Tree-based and Hash-based Indexes - Prof. Yicheng Tu and more Study notes Deductive Database Systems in PDF only on Docsity! Data Indexing Index: a data structure used to speed up selections on data records based on some attributes Example: Index on ‘age’ attribute of Employee table. age is a search key An index consists of data entries that point to some raw data records <key_value, data_pointer> data_pointer raw data Cost of calling pointer to raw data is constant e.g. 1 page I/O Type of Indexes: 1) Tree-based 2) Hash-based 3) Bitmap-based Primary Index vs. Secondary Index Primary: uses the key attribute of a relation as the search key Example: an index based on SSN of Employee table Secondary: search key is NOT the key attribute Example: an index based on ‘age’ of Employee Clustered vs. un-clustered index If the order of data records in file is the same as the order of data entries in the index, that index is called CLUSTERED. Index interface b/w ______________________________________________________ raw data There can only be ONE clustered index a0 p0 a1 p1 a0 a1…. an-1 an Cluster indexes give better performance in searching a range of values.