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cost.rs: simplify cost estimation

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This commit is contained in:
Jussi Saurio
2025-05-10 17:37:58 +03:00
parent 4f07c808b2
commit f12eb25962
1 changed files with 7 additions and 39 deletions
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46
core/translate/optimizer/cost.rs
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@@ -1,5 +1,3 @@
use limbo_sqlite3_parser::ast;
use super::constraints::{Constraint, ConstraintRef};
/// A simple newtype wrapper over a f64 that represents the cost of an operation.
@@ -54,49 +52,19 @@ pub fn estimate_cost_for_scan_or_seek(
);
};
let final_constraint_is_range = usable_constraint_refs.last().map_or(false, |c| {
constraints[c.constraint_vec_pos].operator != ast::Operator::Equals
});
let equalities_count = constraints
let selectivity_multiplier: f64 = usable_constraint_refs
.iter()
.take(if final_constraint_is_range {
usable_constraint_refs.len() - 1
} else {
usable_constraint_refs.len()
.map(|cref| {
let constraint = &constraints[cref.constraint_vec_pos];
constraint.selectivity
})
.count() as f64;
.product();
let cost_multiplier = match (
index_info.unique,
index_info.column_count as f64,
equalities_count,
) {
// no equalities: let's assume range query selectivity is 0.4. if final constraint is not range and there are no equalities, it means full table scan incoming
(_, _, 0.0) => {
if final_constraint_is_range {
0.4
} else {
1.0
}
}
// on an unique index if we have equalities across all index columns, assume very high selectivity
(true, index_cols, eq_count) if eq_count == index_cols => 0.01,
(false, index_cols, eq_count) if eq_count == index_cols => 0.1,
// some equalities: let's assume each equality has a selectivity of 0.1 and range query selectivity is 0.4
(_, _, eq_count) => {
let mut multiplier = 1.0;
for _ in 0..(eq_count as usize) {
multiplier *= 0.1;
}
multiplier * if final_constraint_is_range { 4.0 } else { 1.0 }
}
};
// little bonus for covering indexes
// little cheeky bonus for covering indexes
let covering_multiplier = if index_info.covering { 0.9 } else { 1.0 };
estimate_page_io_cost(
cost_multiplier
selectivity_multiplier
* ESTIMATED_HARDCODED_ROWS_PER_TABLE as f64
* input_cardinality
* covering_multiplier,