Which statement explains index write overhead on a table?

Which statement explains index write overhead on a table?

• A. They must be updated on every insert, update, or delete, turning one write into multiple disk operations.
• B. They are never updated after creation.
• C. They improve write speed by avoiding disk writes.
• D. They only affect read operations.

Answer: (A)

Index write overhead comes from the need to keep the index in sync with every change to the table. When you insert, update, or delete a row, the database must also update the corresponding index entries so they correctly point to the right data. This typically involves traversing the index structure (often a B-tree), adding or removing index entries, and possibly rebalancing or splitting pages. All of these actions generate additional disk I/O and log activity, so a single logical write can become multiple physical writes. That’s why writes carry extra cost even though the index helps reads by allowing faster data lookup. The other statements don’t fit. Indices do get updated after data changes; they aren’t immutable. While they speed up reads, they don’t speed up writes—they usually slow them down because of the extra maintenance work. And while the main benefit of indices is in reads, they do have a direct impact on writes due to the work needed to update them.

Index write overhead comes from the need to keep the index in sync with every change to the table. When you insert, update, or delete a row, the database must also update the corresponding index entries so they correctly point to the right data. This typically involves traversing the index structure (often a B-tree), adding or removing index entries, and possibly rebalancing or splitting pages. All of these actions generate additional disk I/O and log activity, so a single logical write can become multiple physical writes. That’s why writes carry extra cost even though the index helps reads by allowing faster data lookup.

The other statements don’t fit. Indices do get updated after data changes; they aren’t immutable. While they speed up reads, they don’t speed up writes—they usually slow them down because of the extra maintenance work. And while the main benefit of indices is in reads, they do have a direct impact on writes due to the work needed to update them.