What causes "Failed to load position snapshot: {e}" in nautechsystems/nautilus_trader?

Verify the database is reachable and the connection pool is healthy (run a trivial `SELECT 1` with the same pool).

Failed to load position snapshot: {e}

Error message

Failed to load position snapshot: {e}

What it means

This error wraps any sqlx failure that occurs when loading a single row from the `position` table by its id into a `PositionSnapshot`. The library throws it because the underlying database driver error (connection loss, missing table, type mismatch, etc.) is converted into an `anyhow::Error` with context so callers get a clear message. It indicates the SELECT query itself failed at the database level, not that the position was absent (absence returns `Ok(None)`).

Source

Thrown at crates/infrastructure/src/sql/queries.rs:568

            .await
            .map_err(|e| anyhow::anyhow!("Failed to commit transaction: {e}"))
    }

    /// Loads a `PositionSnapshot` entry by `position_id` via the provided `pool`.
    ///
    /// # Errors
    ///
    /// Returns an error if the SQL SELECT or deserialization fails.
    pub async fn load_position_snapshot(
        pool: &PgPool,
        position_id: &PositionId,
    ) -> anyhow::Result<Option<PositionSnapshot>> {
        sqlx::query_as::<_, PositionSnapshotRow>(r#"SELECT * FROM "position" WHERE id = $1"#)
            .bind(position_id.to_string())
            .fetch_optional(pool)
            .await
            .map(|row| row.map(|row| row.0))
            .map_err(|e| anyhow::anyhow!("Failed to load position snapshot: {e}"))
    }

    /// Checks if an `OrderInitialized` event exists for the given `client_order_id` via the provided `pool`.
    ///
    /// # Errors
    ///
    /// Returns an error if the SQL SELECT operation fails.
    pub async fn check_if_order_initialized_exists(
        pool: &PgPool,
        client_order_id: ClientOrderId,
    ) -> anyhow::Result<bool> {
        sqlx::query(r#"
            SELECT EXISTS(SELECT 1 FROM "order_event" WHERE client_order_id = $1 AND kind = 'OrderInitialized')
        "#)
            .bind(client_order_id.to_string())
            .fetch_one(pool)
            .await
            .map(|row| row.get(0))

View on GitHub (pinned to 18893faf8b)

Solutions

Verify the database is reachable and the connection pool is healthy (run a trivial `SELECT 1` with the same pool).
Check the `position` table schema matches `PositionSnapshotRow` fields/column types; run pending migrations.
Confirm `position_id.to_string()` produces the exact id format stored in the table.
Inspect the wrapped sqlx error text in `{e}` to identify the precise driver cause.
Retry the snapshot load; transient network errors are common during reconciliation.

Example fix

// before
let snap = load_position_snapshot(&pool, position_id).await?;
// after
let snap = match load_position_snapshot(&pool, position_id).await {
    Ok(s) => s,
    Err(e) => { tracing::error!("snapshot load failed: {e:#}"); return Err(e); }
};

Defensive patterns

Strategy: try-catch

Validate before calling

// Rust: verify connectivity before loading
sqlx::query("SELECT 1").execute(pool).await
    .map_err(|e| anyhow::anyhow!("db unreachable: {e}"))?;
sqlx::query(r#"SELECT EXISTS(SELECT 1 FROM "position")"#)
    .fetch_one(pool).await
    .map_err(|e| anyhow::anyhow!("position table missing: {e}"))?;

Type guard

fn is_connectivity_error(e: &anyhow::Error) -> bool {
    e.to_string().contains("connection") || e.to_string().contains("timed out")
}

Try / catch

match load_position_snapshot(&pool, position_id).await {
    Ok(Some(snap)) => { /* use snapshot */ }
    Ok(None) => { /* position absent — normal path */ }
    Err(e) if is_connectivity_error(&e) => { /* retry with backoff */ }
    Err(e) => return Err(e.context("position snapshot load")),
}

Prevention

Run schema migrations before starting reconciliation.
Health-check the pool with SELECT 1 before batch reads.
Pin database and driver versions across environments.
Log the full error chain ({e:#}) to preserve the sqlx cause.

When it happens

Trigger: Calling `load_position_snapshot(pool, position_id)` when the database connection is broken, the `position` table/schema does not match `PositionSnapshotRow`, the id string cannot be compared to the column type, or the row fails to deserialize into `PositionSnapshotRow`.

Common situations: Postgres is down or restarting during reconciliation startup; a schema migration drifted from the Rust row struct; connecting to the wrong database (empty schema); wrong SSL credentials causing connection failures mid-query.

Understand the failure class

Background: Database query failed: Internal Server Error 500s wrapping SQL, Prisma, and connection failures — what to check first — this error's family across 16 libraries.

Related errors

AI-assisted analysis of nautechsystems/nautilus_trader@18893faf8b (2026-09-08). Data as JSON: /api/errors/cf6d18c5262c51a9. Report an issue: GitHub.