In agentic systems, Fan-in is the crucial synchronization step that follows a “fan-out” in a parallel execution pattern. After multiple independent tasks have been executed concurrently, the orchestrator must “fan in” their outputs, collecting and consolidating the results from all the parallel branches.
The fan-in process has four primary responsibilities:
- Collect Results: Gather the outputs from all successfully completed branches.
- Handle Failures: Explicitly manage the outcomes of any branches that failed or timed out. This could involve retrying the failed branch, proceeding with a partial result set, or failing the entire workflow.
- Order Results: If the sequence of results matters for the next step, the fan-in process must reorder the outputs, which may have arrived at different times.
- Merge & Continue: Combine the various outputs into a single, coherent data structure that can be used by the next agent or step in the workflow.
The complexity of the fan-in step is a major trade-off of parallel execution. It requires robust logic for handling partial failures to avoid silent errors where, for example, a failed branch is simply ignored. Furthermore, a pre-defined merging strategy (e.g., concatenation, voting, structured aggregation) is necessary to make sense of the multiple, independent results.
Connections
- Parallel Execution (Agentic)
- Fan-out (Agentic)
- Merging Strategies (Agentic)
- Partial Failure Handling