Database_Indexing_AND ITTS TYPES PRESENTATION
- 1. DATABASE INDEXING • Indexing is used to optimize the performance of a database by minimizing the number of disk accesses required when a query is processed. • The index is a type of data structure. It is used to locate and access the data in a database table quickly. • Indexes are a powerful tool used in the background of a database to speed up querying. They provide a method to quickly look up the requested data. • Simply put, an index is a pointer to data in a table. An index in a database is very similar to an index in the back of a book.
- 2. WHY ARE INDEXES NEEDED? • Imagine walking into the Library of Congress and being given the task of finding a specific publishing within 10 minutes. Would you be able to complete this task within the given time frame? • The Library of Congress houses approximately 170 million items. The first thing one would do is access the library’s index because indexes contain all the necessary information needed to access items quickly and efficiently. • Similarly, a database index contains all the necessary information to access data quickly. Some tech giants process hundreds of petabytes of data per day, and efficient access is crucial. Indexes serve as lookup tables that store data efficiently for quicker retrieval.
- 3. INDEX STRUCTURE • 1. Search Key - Contains a copy of the primary key or candidate key of the table. These are stored in sorted order. • 2. Data Reference - Contains pointers holding the address of the disk block where the value of the key can be found.
- 5. 1. ORDERED INDICES • To enhance search efficiency, indices are often sorted for faster retrieval. Example • Consider a table of employees with thousands of records, where each record is 10 bytes in size. Suppose employee IDs start sequentially from 1, 2, 3, and so on. – Without an index: The database must scan sequentially until it reaches ID 543, reading 543 × 10 = 5,430 bytes. – With an index: If each index entry is 2 bytes, the DBMS only needs to read 542 × 2 = 1,084 bytes, making the search much faster.
- 6. 2. PRIMARY INDEX • If an index is created using the primary key of a table, it is called Primary Indexing. • These primary keys are unique, and searching performance is efficient. • Primary indexes can be: 1. Dense Index 2. Sparse Index
- 7. 2. PRIMARY INDEX 1. Dense Index - Contains an index record for every search key value. Faster searching but requires more space.
- 8. 2. PRIMARY INDEX 2. Sparse Index - Index records appear for only some values, reducing space usage but requiring additional sequential searching.
- 9. 3. CLUSTERING INDEX • A Clustering Index is used when an index is created on non-primary key columns that may not be unique. A combination of columns is used to form a unique index. • Example: Employees grouped by Dept_ID form clusters, and the index points to the entire cluster instead of individual records.
- 10. CLUSTERED INDEX
- 11. SECONDARY INDEX • As table size grows, mapping in a sparse index also grows. Secondary indexing introduces another level of indexing to improve efficiency. - The first level index maps broad ranges and is stored in primary memory. - The second level index further divides ranges and is stored in secondary memory.
- 12. SECONDARY INDEX • Searching for Roll No. 111: • Find the highest entry ≤ 111 in Level 1 (gets 100). • In Level 2, find the highest ≤ 111 (gets 110). • Using address 110, search the data block until Roll No. 111 is found. • This hierarchical structure improves search efficiency.
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