Enum EmitClause 

pub enum EmitClause {
    AfterWatermark,
    OnWindowClose,
    Periodically {
        interval: Box<Expr>,
    },
    OnUpdate,
    Changes,
    Final,
}

EMIT clause for controlling output timing.

This is the SQL AST representation of emit strategies. See laminar_core::operator::window::EmitStrategy for the runtime representation.

Variants

AfterWatermark

EMIT AFTER WATERMARK (or EMIT ON WATERMARK)

Emit results when the watermark passes the window end. This is the most efficient strategy.

OnWindowClose

EMIT ON WINDOW CLOSE

For append-only sinks (Kafka, S3, Delta Lake, Iceberg). Only emits when window closes, no intermediate results. Unlike AfterWatermark, this is NOT a synonym - it has distinct behavior.

Periodically

EMIT EVERY INTERVAL ‘N’ unit (or EMIT PERIODICALLY)

Emit intermediate results at fixed intervals. Final results are still emitted on watermark.

Fields

interval: Box<Expr>

The interval expression (e.g., INTERVAL ‘5’ SECOND)

OnUpdate

EMIT ON UPDATE

Emit updated results after every state change. This provides lowest latency but highest overhead.

Changes

EMIT CHANGES

Emit changelog records with Z-set weights for CDC pipelines. Every emission includes operation type and weight:

• Insert (+1 weight)
• Delete (-1 weight)
• Update (retraction pair: -1 old, +1 new)

Required for:

• CDC pipelines
• Cascading materialized views
• Downstream consumers that need to track changes

Final

EMIT FINAL

Suppress ALL intermediate results, emit only finalized. Also drops late data entirely after window close. Use for BI reporting where only final, exact results matter.

Implementations

impl EmitClause

pub fn to_emit_strategy(&self) -> Result<EmitStrategy, ParseError>

Convert to runtime EmitStrategy.

Errors

Returns ParseError::WindowError if the periodic interval cannot be parsed.

pub fn requires_changelog(&self) -> bool

Check if this emit strategy requires changelog/retraction support.

pub fn is_append_only(&self) -> bool

Check if this emit strategy is append-only (no retractions).

pub fn requires_watermark(&self) -> bool

Returns true if this emit strategy requires a watermark on the source.

OnWindowClose, Final, and AfterWatermark all depend on watermark advancement to trigger window closure. Without a watermark, timers will never fire and windows will never close.

Trait Implementations

impl Clone for EmitClause

fn clone(&self) -> EmitClause

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for EmitClause

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Display for EmitClause

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl PartialEq for EmitClause

fn eq(&self, other: &EmitClause) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl StructuralPartialEq for EmitClause