Why might you want to update an existing index instead of deleting it?

Updating an existing index rather than deleting it can be beneficial because updating allows for better indexing without disrupting ongoing queries. When an index is updated, it can be refined or adjusted based on changes to the underlying data and usage patterns while allowing the database to continue executing queries using that index. This can be especially helpful in maintaining performance and ensuring that query execution plans remain optimal.

In contrast, deleting an index can lead to a temporary decrease in performance, as queries that relied on that index may need to execute without it, potentially leading to full collection scans. Therefore, the ability to update an index while preserving its availability for query operations is a significant advantage.

Other options mention various aspects of index management, but they do not capture the core benefit of the seamless continuity of query performance that an update provides, which is why updating an index is often preferred over deleting one.