Indekser

Indekser are data structures and mechanisms that enable fast access to data by mapping search keys to their corresponding records. They are used to speed up data retrieval in databases, information retrieval systems, search engines, and in various types of catalogs or registries. By organizing data to be quickly searchable, indekser reduce the need to scan every row or document.

Common types include B-tree and variants such as B+-tree, which support ordered data and range queries; primary or clustered indexes define the physical order of rows, while secondary or non-clustered indexes store pointers to data. Hash indexes provide fast equality lookups but are not suitable for range scans. Inverted indexes are essential for full-text search, listing terms and the documents that contain them. Bitmap indexes are useful for low-cardinality columns in data warehouses. Spatial indexes like R-tree variants help with geographic data.

Indexes are created based on query patterns; while they speed reads, they add storage overhead and slow down inserts, updates, and deletes due to maintenance. The choice and number of indekser must balance read performance against write cost and storage. Database optimizers use statistics about index selectivity to choose which indexes to use.

In relational databases, indexes are created on columns to accelerate lookups and joins. Search engines build inverted indekser over text to support keyword queries. Libraries and catalogs use indexes to locate items efficiently. Important considerations include keeping indexes up to date and reindexing when data changes.