Does Indexing Boolean Fields Offer Real Performance Benefits?

Performance Benefits of Indexing Boolean Fields

In many database systems, a common assumption is that indexing Boolean fields does not provide any significant performance gain. However, real-world scenarios may challenge this notion.

Performance for Retrieving Specific Records

Consider a query with a WHERE clause filtering on a Boolean field, such as WHERE isok=1. When there are minimal records matching this condition, an index may not offer a noticeable benefit. The engine can quickly scan through the table to locate the relevant rows.

Performance for Large Datasets

However, when dealing with vast datasets with a small percentage of records meeting the Boolean condition, an index can dramatically improve performance. The engine avoids scanning through the entire table by utilizing the index to efficiently retrieve the desired records.

In such cases, the engine can quickly and precisely locate the relevant table pages by traversing the index. This selective approach significantly reduces the time spent scanning irrelevant pages, resulting in substantial query speed-up.

Example:

As demonstrated in a practical example, a query on a table with 4 million rows searching for approximately 1000 rows with a specific Boolean flag was significantly accelerated by adding an index on the Boolean field. Query execution time dropped from over 9 seconds to a fraction of a second.

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