Struct CostConstants 

#[non_exhaustive]
pub struct CostConstants { /* private fields */ }

Engine-specific cost constants the handlerton returns from get_cost_constants.

Both fields mirror the per-storage-engine values MySQL stores in the mysql.engine_cost table; the defaults match what SE_cost_constants(Optimizer::kOriginal) would have produced on the C++ side, so an engine that supplies only one field starts from a sane fallback for the other.

Implementations

impl CostConstants

pub const fn new(memory_block_read_cost: f64, io_block_read_cost: f64) -> Self

Construct a cost-constants tuple with the given per-block read costs. Both values must be positive; MySQL’s SE_cost_constants::set rejects zero or negative values with INVALID_COST_VALUE, so the shim does the same and an engine returning either value reverts to the defaults.

pub const fn defaults() -> Self

The defaults SE_cost_constants(Optimizer::kOriginal) initialises — memory_block_read_cost = 0.25, io_block_read_cost = 1.0. Engines that want to override one field commonly start from these.

pub const fn memory_block_read_cost(&self) -> f64

Cost of reading one random block from an in-memory buffer.

pub const fn io_block_read_cost(&self) -> f64

Cost of reading one random block from disk.

Trait Implementations

impl Clone for CostConstants

fn clone(&self) -> CostConstants

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for CostConstants

impl Debug for CostConstants

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

Formats the value using the given formatter.

impl Default for CostConstants

fn default() -> Self

Returns the “default value” for a type.

impl PartialEq for CostConstants

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