nautechsystems/nautilus_trader · error

Cannot setup bar aggregator: no aggregator found for {bar_ty

Error message

Cannot setup bar aggregator: no aggregator found for {bar_type}

What it means

setup_bar_aggregator requires an already-created aggregator in the bar_aggregators map for the given BarType/key. This function only configures (historical mode, handler, sequence validation) an existing aggregator; it never creates one. If none exists, the caller invoked setup out of order.

Source

Thrown at crates/data/src/engine/mod.rs:5051

            );
            return Some(SubscribeCommand::Quotes(subscribe));
        }

        None
    }

    /// Sets up a bar aggregator.
    ///
    /// This method handles historical mode, message bus subscriptions, and time bar aggregator setup.
    fn setup_bar_aggregator(
        &self,
        bar_type: BarType,
        historical: bool,
        request_id: Option<UUID4>,
    ) -> anyhow::Result<()> {
        let key = bar_aggregator_key(bar_type, request_id);
        let aggregator = self.bar_aggregators.get(&key).ok_or_else(|| {
            anyhow::anyhow!("Cannot setup bar aggregator: no aggregator found for {bar_type}")
        })?;

        // Set historical mode and handler
        let cache = self.cache.clone();
        let validate_sequence = self.config.validate_data_sequence;
        let publish = !historical;
        let handler: Box<dyn FnMut(Bar)> = Box::new(move |bar: Bar| {
            process_engine_bar(&cache, validate_sequence, publish, bar);
        });

        aggregator
            .borrow_mut()
            .set_historical_mode(historical, handler);

        // For TimeBarAggregator, set clock and start timer
        if bar_type.spec().is_time_aggregated() {
            use nautilus_common::clock::TestClock;

View on GitHub (pinned to 18893faf8b)

Solutions

1. Ensure start_bar_aggregation (or the create step) is called for the bar_type before setup_bar_aggregator.
2. Check that the same request_id is passed to both creation and setup — a None vs Some(UUID4) mismatch changes the key.
3. If the aggregator was stopped, recreate it via start_bar_aggregation rather than re-running setup.
4. Inspect bar_aggregators keys (via debug logging) to confirm the expected key exists.

Example fix

// before
engine.setup_bar_aggregator(bar_type, historical, request_id);
// after
engine.start_bar_aggregation(bar_type, None, false)?;
engine.setup_bar_aggregator(bar_type, historical, request_id)?;

// ensure aggregation was started before setup
engine.start_bar_aggregation(bar_type, None, false)?;
engine.setup_bar_aggregator(bar_type, historical, request_id)?;

When it happens

Trigger: Calling setup_bar_aggregator (internal, from subscribe_bars handler wiring or replay paths) before start_bar_aggregation/create_bar_aggregator_for_key ran, or after stop_bar_aggregator removed the entry, or with a request_id that doesn't match the one used at creation.

Common situations: Replay/backtest code paths setting up aggregation twice; calling stop then setup on the same bar type; mismatched request_id between create and setup calls.

Understand the failure class

Background: "Invalid state transition" errors: "status must be X, actually Y", "already rejected/charging/uninstalled", "cannot ... while running" — what they mean when a library rejects your call — this error's family across 31 libraries.

Related errors

• Cannot request aggregated bars: one of the aggregators in `b
• Cannot start bar aggregation: no instrument found for {}
• Cannot start bar aggregation for {bar_type}
• Cannot stop bar aggregator: no aggregator to stop for {bar_t
• No live aggregator for continuous future subscription {}

AI-assisted analysis of nautechsystems/nautilus_trader@18893faf8b (2026-09-08). Data as JSON: /api/errors/8522e720eacc57f3. Report an issue: GitHub.