Struct PlanCache 

pub struct PlanCache {
    pub hits: u64,
    pub misses: u64,
    /* private fields */
}

LRU-ish plan cache keyed by canonical query hash.

Mission F: uses FxHashMap. The keys are u64 hashes (already pre-hashed by canonicalize), so SipHash is pure overhead — Fx is much cheaper for the integer-keyed lookup.

Fields

hits: u64

misses: u64

Implementations

impl PlanCache

pub fn new(capacity: usize) -> Self

pub fn insert(&mut self, hash: u64, plan: PlanNode)

Store a planned query under its canonical hash. The plan can have any literal values inside it — those will be overwritten on hit.

pub fn get_with_substitution( &mut self, hash: u64, literals: &[Literal], ) -> Option<PlanNode>

Look up a plan by canonical hash and return a clone with the new literals substituted into every Expr::Literal slot in source order.

Returns Some(plan) on a hit and bumps self.hits. Returns None on a miss and bumps self.misses. Returning None instead of reaching for the planner here keeps this module dependency-free from planner — the engine handles the miss path.

The substitution is done on a clone of the cached plan, not the stored copy. The cached plan stays pristine for the next call.

pub fn len(&self) -> usize

pub fn is_empty(&self) -> bool

pub fn clear(&mut self)