What causes "Failed to send query add_order to database message handler: {e}" in nautechsystems/nautilus_trader?

Ensure the adapter is connected and its task running before adding orders.

Failed to send query add_order to database message handler:

Error message

Failed to send query add_order to database message handler: {e}

What it means

Thrown by `add_order` when the `DatabaseQuery::AddOrder` message (the order's initialized event plus optional client_id) cannot be sent over the mpsc channel to the database message-handler task, i.e. the receiver was dropped. The order is not persisted.

Source

Thrown at crates/infrastructure/src/sql/cache.rs:951

                )
            })
    }

    fn add_synthetic(&self, _synthetic: &SyntheticInstrument) -> anyhow::Result<()> {
        todo!()
    }

    fn add_account(&self, account: &AccountAny) -> anyhow::Result<()> {
        let query = DatabaseQuery::AddAccount(account_last_event(account)?, false);
        self.tx.send(query).map_err(|e| {
            anyhow::anyhow!("Failed to send query add_account to database message handler: {e}")
        })
    }

    fn add_order(&self, order: &OrderAny, client_id: Option<ClientId>) -> anyhow::Result<()> {
        let query = DatabaseQuery::AddOrder(order_initialized_event(order), client_id);
        self.tx.send(query).map_err(|e| {
            anyhow::anyhow!("Failed to send query add_order to database message handler: {e}")
        })
    }

    fn add_order_snapshot(&self, snapshot: &OrderSnapshot) -> anyhow::Result<()> {
        let query = DatabaseQuery::AddOrderSnapshot(snapshot.to_owned());
        self.tx.send(query).map_err(|e| {
            anyhow::anyhow!(
                "Failed to send query add_order_snapshot to database message handler: {e}"
            )
        })
    }

    fn add_position(&self, position: &Position) -> anyhow::Result<()> {
        let event = position_last_event(position)?;
        let query = DatabaseQuery::AddPosition(position.id, event);
        self.tx.send(query).map_err(|e| {
            anyhow::anyhow!("Failed to send query add_position to database message handler: {e}")
        })

View on GitHub (pinned to 18893faf8b)

Solutions

Ensure the adapter is connected and its task running before adding orders.
Check logs for a panic in the message-handler task.
Reconnect/restart the adapter and retry the write.
Fix shutdown ordering so the cache database closes after trading logic.

Defensive patterns

Strategy: try-catch

Validate before calling

if not cache_db_adapter.is_running:
    raise RuntimeError("Cannot add_order: adapter not running")

Try / catch

try:
    cache.add_order(order, client_id)
except RuntimeError as e:
    logger.error("Order persistence failed (writer stopped): %s", e)

Prevention

Ensure the adapter is healthy before order submission flows
Never disconnect the cache database while trading is live
Alert on writer-task panics
Buffer orders for retry if the writer is down

When it happens

Trigger: Calling `add_order` (via `py_add_order`) when the writer task has exited or panicked, so `tx.send` returns a SendError.

Common situations: Adding orders while the cache database adapter is stopping; handler thread crashed earlier in the session.

Related errors

AI-assisted analysis of nautechsystems/nautilus_trader@18893faf8b (2026-09-08). Data as JSON: /api/errors/05d15b71d66640d2. Report an issue: GitHub.