How Can Database Indexing Significantly Improve Query Performance in Large Datasets?

Database index: the key to improving query performance on large data sets

Database indexing technology improves query performance by sorting records based on specific criteria. It utilizes auxiliary data structures to map index values ​​to record locations, thereby avoiding time-consuming full table scans of the entire table when searching for specific data.

The necessity of index

As the data set grows, the time required for linear search increases significantly. For example, searching in a data set containing 5 million unsorted records requires accessing an average of 2.5 million data blocks. However, once the search field is indexed, binary searches can be used, reducing the average number of block accesses to only 20.

How indexes work

Indexes are created by generating additional data structures that store the index field values ​​and their corresponding record pointers. These index structures are themselves ordered and facilitate efficient binary searches. For example, consider a table with 5 million records and an index on the "firstName" field. The index structure will contain 5 million records, each containing the "firstName" value and a 4-byte pointer to the original record.

Advantages of Index

• Faster query performance: Binary searches using index fields require significantly fewer data block accesses compared to linear searches, resulting in faster query execution.
• Reduced resource consumption: Indices take up less disk space than the original table because they only contain index field values ​​and pointers. This reduces the number of data blocks accessed during queries, saving system resources.
• Improving scalability: As the database grows, indexes become increasingly valuable because the performance gap between sorted and unsorted searches increases.

When to use indexes

Indexes are most effective on fields that are frequently used in search queries and have high cardinality (i.e., have a wide range of unique values). Avoiding indexing on low-cardinality fields or fields that are used only for output can prevent performance degradation.

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