What type of code does the Thrift client for Cassandra return when a row isn't found?

The Thrift client for Cassandra returns a specific type of code when a requested row is not found, which is the "NotFound" code. This indicates to the client that the query executed did not yield any results for the requested key or row.

In the context of database queries, it is essential for clients to receive precise feedback regarding the state of their query execution. The "NotFound" response is particularly useful in scenarios where clients need to differentiate between various states of the query outcome. Recognizing that a row simply does not exist allows developers to implement appropriate handling in their applications, such as creating new entries or alerting users about the absence of expected data.

Other response codes like "Error," "Unavailable," or "Success" are indicative of different situations. "Error" might suggest that something went wrong during the request, rather than a simple absence of data. "Unavailable" would indicate that the Cassandra cluster cannot currently handle the request due to unavailability of nodes or other issues beyond just not finding a row. "Success" implies that the query executed and returned some result. Therefore, "NotFound" is indeed the most precise and suitable response for a case where the requested row does not exist in the database.