Struct PlanCost 

pub struct PlanCost {
    pub rows: u64,
    pub cpu_cost: f64,
    pub gpu_mem: u64,
    pub transfers: u32,
}

Cost estimate for a query plan node.

Captures the multi-dimensional cost of executing a plan node, enabling the optimizer to make informed decisions based on available resources.

Fields

rows: u64

Estimated number of output rows.

cpu_cost: f64

Estimated CPU cost (arbitrary units, relative comparisons only).

This represents processing overhead that cannot be parallelized on the GPU, such as coordination, scheduling, and result materialization.

gpu_mem: u64

Estimated GPU memory usage in bytes.

Includes both input buffers and intermediate storage required for the operation.

transfers: u32

Number of GPU-to-host or host-to-GPU data transfers.

Transfers are typically the most expensive operations in GPU computing and should be minimized.

Implementations

impl PlanCost

pub fn with_rows(rows: u64) -> Self

Creates a new cost estimate with specified row count.

pub fn total_cost(&self, transfer_weight: f64) -> f64

Computes a scalar cost value for comparison purposes.

The formula weights different cost components:

• CPU cost is taken directly
• GPU memory is scaled by 0.001 (1GB = 1M cost units)
• Transfers are heavily weighted due to their high latency

Arguments

• transfer_weight - Weight multiplier for transfer costs

pub fn then(self, other: PlanCost) -> PlanCost

Combines two costs representing sequential operations.

Row count comes from the second (later) operation; other costs are summed.

Trait Implementations

impl Clone for PlanCost

fn clone(&self) -> PlanCost

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for PlanCost

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

Formats the value using the given formatter.

impl Default for PlanCost

fn default() -> PlanCost

Returns the “default value” for a type.

impl PartialEq for PlanCost

fn eq(&self, other: &PlanCost) -> 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 PlanCost