Are there any contraindications for using indexes in databases?

Yes, they exist. The use of indexes has several contraindications and limitations:

• Increased disk space: Indexes are stored separately from the table data and require additional disk space. For large tables and many indexes, this can be significant.
• Slowing down write operations: When inserting, updating, and deleting data in the table, the corresponding indexes must also be updated. This adds overhead and slows down these operations.
• Index maintenance: Indexes require regular maintenance (rebuilding, analysis) to maintain optimal performance, especially on tables with high modification frequency.
• Unused indexes: Indexes that are not used or rarely used only add overhead during write operations and occupy space without benefiting read operations. It is important to delete unused indexes.
• Indexing small tables: For tables with a small number of rows (e.g., less than a few hundred), a full table scan may be faster than searching by index due to the overhead of accessing the index.
• Columns with low cardinality: Indexing columns with very few unique values (e.g., boolean fields) is usually ineffective, as the index will contain many identical values and cannot quickly filter data.
• Composite indexes: The order of columns in a composite index is important. If queries do not use the index prefix, the index may be ineffective.

Conclusion: Indexes are useful for speeding up read operations, but they should be used thoughtfully, considering maintenance costs, impact on write operations, and data characteristics.