request ID
also: request number, operation ID, I/O ID, transaction ID
A unique identifier assigned to a system request or I/O operation, used to track and correlate it throughout its lifecycle in the kernel or application.
A request ID is a numerical or alphanumeric identifier that the kernel or an application assigns to distinguish one operation from another. It allows the system to match responses with their corresponding requests, especially important in asynchronous I/O where a request may be submitted and completed out of order.
Request IDs are commonly used in disk I/O, network operations, and system calls. For example, when you submit multiple asynchronous read operations to a storage device, each receives a unique request ID that helps the kernel track completion of each specific operation.
You may encounter request IDs in system tracing tools like strace, in kernel logs, or when examining detailed I/O statistics with tools like iostat or iotop. Developers working with asynchronous APIs also use request IDs to correlate sent requests with received responses.