Trait WindowStateObserver 

pub trait WindowStateObserver: Send + Sync {
    // Required method
    fn finalize_window_aggregate(
        &self,
        partition_idx: usize,
        window_expr: &Arc<dyn WindowExpr>,
        partition_key: &PartitionKey,
        state: Vec<ScalarValue>,
    ) -> Result<()>;
}

Callback receiver for per-partition window state.

state is the result of Accumulator::state, which is a &mut self call whose trait doc states “this function should not be called twice.” Several built-in aggregates (median, percentile_cont, string_agg, min_max_bytes/min_max_struct) std::mem::take their internal buffers to build that state — so state is a destructive read, not a snapshot. The exec fires this at most once per group; a callee that needs the value beyond the callback must retain it (e.g. clone into owned storage).

Required Methods

fn finalize_window_aggregate( &self, partition_idx: usize, window_expr: &Arc<dyn WindowExpr>, partition_key: &PartitionKey, state: Vec<ScalarValue>, ) -> Result<()>

Invoked once per (output-partition-index, window-expression, PARTITION BY tuple) as each PARTITION BY group closes, for every aggregate window expression on the exec. Non-aggregate window functions (e.g. row_number, rank, lead/lag) do not fire this callback.

Arguments

• partition_idx - Output partition index of the BoundedWindowAggExec stream firing this callback.
• window_expr - The window expression whose state just closed.
• partition_key - The PARTITION BY tuple that just closed.
• state - Accumulator::state for the closed group of window_expr. See the trait-level doc for the destructive-read contract.

Dyn Compatibility

This trait is dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementors