ajoin

Ajoin is a term used in computer science to describe an operation that combines two data sources or streams on a common key, with a focus on asynchronous or non-blocking execution. It is not a standard SQL keyword and does not refer to a single, universally defined function; instead, it appears as a label in various libraries, frameworks, or documentation to denote an async join pattern.

In database and data-processing contexts, ajoin typically refers to joining data as it becomes available, using streaming or event-driven techniques. This contrasts with traditional batch joins that require all input data to be present before the result is produced. Ajoin implementations often rely on windowing, state stores, handling late data, and tolerating out-of-order events. Common concerns include balancing throughput with latency, managing memory for state, and ensuring deterministic results.

In programming libraries, an ajoin function may provide a non-blocking merge of two asynchronous sequences or futures, returning a result when matching elements are present. Examples can include reactive streams, futures-based APIs, or dataflow engines where the join operation is integrated into the event loop or scheduler.

Terminology varies; ajoin is sometimes described as an asynchronous join or async join, and different communities may use different naming conventions. See also join, inner join, left join, and asynchronous programming.