What can lead to a decrease in query performance when using indexes?

Degradation of query performance when using indexes can be caused by several factors:

• Inappropriate index choice: if the index does not match the query conditions, the DBMS may not use the index effectively.
• Index fragmentation: over time, the index can become fragmented, slowing down access.
• High update volume: frequent inserts, updates, and deletes can slow down index operations.
• Use of functions or operations on indexable fields: for example, applying functions to a column in a WHERE clause can lead to index ignoring.
• Too many indexes: excessive indexes slow down write operations and can affect query execution plans.

In Go (Golang), when working with databases through ORM or drivers, it is important to design queries and indexes properly to avoid such issues.