Skip to content

AnswerSynthesizerNode

Overview

  • Summarizes aggregated results into a user‑facing response using an LLM.
  • Exists to convert structured results into human‑readable output.
  • Sits after EngineAggregatorNode at the end of the control graph.
  • Class: AnswerSynthesizerNode
  • Source: packages/nl2sql/src/nl2sql/pipeline/nodes/answer_synthesizer/node.py

Responsibilities

  • Serialize aggregated results for prompt input.
  • Include unmapped sub‑queries in the response context.
  • Invoke LLM with structured output schema.

Position in Execution Graph

Upstream: - EngineAggregatorNode

Downstream: - Graph end.

Trigger conditions: - Executed after aggregation completes.

flowchart LR
    Aggregator[EngineAggregatorNode] --> Synthesizer[AnswerSynthesizerNode] --> EndNode[PipelineEnd]

Inputs

From GraphState:

  • user_query (required)
  • aggregator_response.terminal_results (required)
  • decomposer_response.unmapped_subqueries (optional)

Validation performed:

  • If no aggregated result is available, emits INVALID_STATE.

Outputs

Mutations to GraphState:

  • answer_synthesizer_response (AnswerSynthesizerResponse)
  • reasoning summary
  • errors on failure

Side effects:

  • LLM invocation.

Internal Flow (Step-by-Step)

  1. Resolve aggregated result from aggregator_response.
  2. If missing, emit INVALID_STATE error and stop.
  3. Serialize results to JSON.
  4. Serialize unmapped sub‑queries to JSON.
  5. Invoke LLM chain with structured output.
  6. Return AnswerSynthesizerResponse.
  7. On exception, emit AGGREGATOR_FAILED.

Contracts & Interfaces

Implements a LangGraph node callable:

def __call__(self, state: GraphState) -> Dict[str, Any]

Key contracts:

  • AggregatedResponse
  • AnswerSynthesizerResponse

Determinism Guarantees

  • Non‑deterministic unless LLM configured deterministically.

Error Handling

Emits PipelineError with:

  • INVALID_STATE (no aggregated result)
  • AGGREGATOR_FAILED (LLM failure)

Logs failures via logger.error.

Retry + Idempotency

  • No internal retry logic.
  • Idempotency depends on LLM determinism.

Performance Characteristics

  • LLM call dominates latency and cost.
  • Serialization of aggregated results is in‑memory.

Observability

  • Logger: answer_synthesizer
  • Adds reasoning summary to state.

Configuration

  • LLM configuration for agent name answer_synthesizer via llm.yaml.

Extension Points

  • Modify ANSWER_SYNTHESIZER_PROMPT.
  • Replace node in build_graph() for custom synthesis.

Known Limitations

  • No deterministic summarization guarantees without LLM configuration.
  • No fallback response when LLM fails.
  • packages/nl2sql/src/nl2sql/pipeline/nodes/answer_synthesizer/node.py