Function build_trace_dataframe 

async fn build_trace_dataframe(
    ctx: &QueryContextRef,
    instance: &Instance,
    selects: Vec<SelectExpr>,
    filters: Vec<Expr>,
    tags: Option<HashMap<String, Value>>,
    distincts: &[Expr],
) -> Result<DataFrame>

Reads the trace table, or the services or operations lookup table that answers selects and distincts, then projects selects and applies filters and the Jaeger tag filters.