hawdb_optimizer_graph/graph/

lowering.rs

// Copyright 2026 Nowledge
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

use super::{
    access_path::index_seek_from_filter,
    costing::{
        estimate_node_cartesian_product_cost, estimate_physical_plan_cost,
        push_optional_relationship_count_sum_cost_decision,
    },
    logical_rewrite::{rewrite_logical_plan, LogicalRewriteOutput},
    properties::satisfies_ordering,
    selected_trace::selected_plan_trace,
    stages::{
        ACCESS_PATH_SELECTION_STAGE, DIRECT_PHYSICAL_FALLBACK_STAGE, LOGICAL_GROUPING_STAGE,
        PHYSICAL_SEARCH_STAGE, PLAN_FINALIZATION_STAGE, SELECTED_PLAN_COSTING_STAGE,
    },
    LogicalPlanRoot, LoweringReadyLogicalPlanRoot, OptimizationSearchReport, OptimizerCatalog,
    OptimizerConfig, OptimizerTrace, PhysicalPlan, PhysicalPlanRoot, StageStats,
};
use crate::{
    GroupId, Memo, OptimizerContext, OptimizerSearchDirective, OptimizerSearchDirectiveError,
    RuleEvent, RuleOutcome, SelectedPlanTrace, StageTrace,
};
use hawdb_core::Value;
use hawdb_cypher::RelationshipDirection;
use hawdb_plan_cypher::{
    AggregateFunction, AggregateTarget, GraphExpansionBudget, LogicalPlan, NodeProjectionAccess,
    Predicate, Projection, ProjectionExpression, SortItem, SortKey,
};
use std::collections::{BTreeMap, BTreeSet};

mod access;
mod ddl;
mod join;
mod mutation;
mod procedure;
mod simple;
mod traversal;

#[cfg(test)]
mod tests;

type GraphMemo = Memo<GroupExpr>;

#[derive(Debug)]
struct GroupExpr {
    logical: LogicalPlan,
    children: Vec<GroupId>,
}

#[derive(Debug, Default, Clone)]
pub struct CascadesOptimizer {
    context: OptimizerContext,
}

impl CascadesOptimizer {
    pub fn new(config: OptimizerConfig) -> Self {
        Self {
            context: OptimizerContext::from_config(config),
        }
    }

    pub fn with_context(context: OptimizerContext) -> Self {
        Self { context }
    }

    pub fn context(&self) -> &OptimizerContext {
        &self.context
    }

    pub fn refresh_trace_for_physical_plan(
        &self,
        trace: &mut OptimizerTrace,
        plan: &PhysicalPlan,
        catalog: &OptimizerCatalog,
    ) {
        refresh_selected_plan_trace(trace, selected_plan_trace(plan, catalog, &self.context));
    }

    pub fn optimize(&self, logical: &LogicalPlan) -> PhysicalPlan {
        self.optimize_root(&LogicalPlanRoot::new(logical.clone()))
            .into_parts()
            .0
    }

    pub fn optimize_with_trace(&self, logical: &LogicalPlan) -> (PhysicalPlan, OptimizerTrace) {
        self.optimize_root(&LogicalPlanRoot::new(logical.clone()))
            .into_parts()
    }

    pub fn optimize_with_catalog(
        &self,
        logical: &LogicalPlan,
        catalog: &OptimizerCatalog,
    ) -> (PhysicalPlan, OptimizerTrace) {
        self.optimize_root_with_catalog(&LogicalPlanRoot::new(logical.clone()), catalog)
            .into_parts()
    }

    pub fn optimize_root(&self, root: &LogicalPlanRoot) -> PhysicalPlanRoot {
        self.optimize_root_with_catalog(root, &OptimizerCatalog::optimistic())
    }

    pub fn optimize_root_with_catalog(
        &self,
        root: &LogicalPlanRoot,
        catalog: &OptimizerCatalog,
    ) -> PhysicalPlanRoot {
        self.optimize_lowering_ready_root_with_catalog_and_directive(
            &root.clone().into_lowering_ready(),
            catalog,
            OptimizerSearchDirective::Auto,
        )
        .expect("automatic optimizer search cannot reject its directive")
    }

    pub fn optimize_lowering_ready_root_with_catalog(
        &self,
        root: &LoweringReadyLogicalPlanRoot,
        catalog: &OptimizerCatalog,
    ) -> PhysicalPlanRoot {
        self.optimize_lowering_ready_root_with_catalog_and_directive(
            root,
            catalog,
            OptimizerSearchDirective::Auto,
        )
        .expect("automatic optimizer search cannot reject its directive")
    }

    pub fn optimize_root_with_catalog_and_directive(
        &self,
        root: &LogicalPlanRoot,
        catalog: &OptimizerCatalog,
        directive: OptimizerSearchDirective,
    ) -> Result<PhysicalPlanRoot, OptimizerSearchDirectiveError> {
        self.optimize_lowering_ready_root_with_catalog_and_directive(
            &root.clone().into_lowering_ready(),
            catalog,
            directive,
        )
    }

    pub fn optimize_lowering_ready_root_with_catalog_and_directive(
        &self,
        root: &LoweringReadyLogicalPlanRoot,
        catalog: &OptimizerCatalog,
        directive: OptimizerSearchDirective,
    ) -> Result<PhysicalPlanRoot, OptimizerSearchDirectiveError> {
        let rewrite = rewrite_logical_plan(root.plan());
        let logical = rewrite.plan();
        let required_groups = logical_group_count(logical);
        let max_groups = self.context.optimizer_config().max_groups;
        if directive == OptimizerSearchDirective::Memo && required_groups > max_groups {
            return Err(OptimizerSearchDirectiveError::MemoGroupBudgetExceeded {
                required_groups,
                max_groups,
            });
        }
        if directive == OptimizerSearchDirective::DirectFallback
            || (directive == OptimizerSearchDirective::Auto && required_groups > max_groups)
        {
            let mut decisions = Vec::new();
            let mut stage_events = Vec::new();
            let plan = lower_logical(
                logical,
                LoweringChildren::Direct,
                catalog,
                &self.context,
                &mut decisions,
                &mut stage_events,
            );
            let plan = finalize_physical_plan(plan, &mut decisions, &mut stage_events);
            let mut report = if directive == OptimizerSearchDirective::DirectFallback {
                OptimizationSearchReport::forced_direct_fallback(required_groups)
            } else {
                OptimizationSearchReport::direct_fallback(required_groups, max_groups)
            };
            record_logical_rewrite(&mut report, &rewrite);
            report.push_stage_event(
                LOGICAL_GROUPING_STAGE.trace(StageStats::new(1, required_groups)),
            );
            for event in stage_events {
                report.push_stage_event(event);
            }
            report.push_stage_event(
                DIRECT_PHYSICAL_FALLBACK_STAGE.trace(StageStats::new(required_groups, 1)),
            );
            report.extend_decisions(decisions);
            let selected = selected_plan_trace(&plan, catalog, &self.context);
            report.push_stage_event(SELECTED_PLAN_COSTING_STAGE.trace(StageStats::new(1, 1)));
            report.record_selected_plan_cost(selected.cost);
            return Ok(PhysicalPlanRoot::new(plan, report.into_trace(selected)));
        }
        let mut memo = GraphMemo::default();
        let root = insert_logical_group(&mut memo, logical);
        let mut decisions = Vec::new();
        let mut stage_events = Vec::new();
        let plan = best_physical(
            &memo,
            root,
            catalog,
            &self.context,
            &mut decisions,
            &mut stage_events,
        );
        let plan = finalize_physical_plan(plan, &mut decisions, &mut stage_events);
        let mut report = OptimizationSearchReport::memo(memo.group_count());
        record_logical_rewrite(&mut report, &rewrite);
        report
            .push_stage_event(LOGICAL_GROUPING_STAGE.trace(StageStats::new(1, memo.group_count())));
        let (applied_rules, skipped_rules) = stage_rule_counts(&stage_events);
        for event in stage_events {
            report.push_stage_event(event);
        }
        report.push_stage_event(PHYSICAL_SEARCH_STAGE.trace(
            StageStats::new(memo.group_count(), 1).with_rule_counts(applied_rules, skipped_rules),
        ));
        report.extend_decisions(decisions);
        let selected = selected_plan_trace(&plan, catalog, &self.context);
        report.push_stage_event(SELECTED_PLAN_COSTING_STAGE.trace(StageStats::new(1, 1)));
        report.record_selected_plan_cost(selected.cost);
        if directive == OptimizerSearchDirective::Memo {
            report.push_decision("selected memo search: explicit optimizer search directive");
        }
        Ok(PhysicalPlanRoot::new(plan, report.into_trace(selected)))
    }
}

fn refresh_selected_plan_trace(trace: &mut OptimizerTrace, selected: SelectedPlanTrace) {
    let selected_cost = selected.cost.with_cardinality_floor();
    let selected_cost_breakdown = selected.cost_breakdown.with_cardinality_floor();
    let cost_detail = format!(
        "estimated_rows={} cost={}",
        selected_cost.estimated_rows, selected_cost.cost
    );
    let cost_decision = format!("selected physical plan cost: {cost_detail}");
    if let Some(decision) = trace
        .decisions
        .iter_mut()
        .find(|decision| decision.starts_with("selected physical plan cost: "))
    {
        *decision = cost_decision;
    } else {
        trace.decisions.push(cost_decision);
    }
    let cost_event = RuleEvent::selected("physical plan cost", cost_detail);
    if let Some(event) = trace.rule_events.iter_mut().find(|event| {
        event.rule() == "physical plan cost" && event.outcome() == RuleOutcome::Selected
    }) {
        *event = cost_event;
    } else {
        trace.rule_events.push(cost_event);
    }

    trace.query_digest = selected.query_digest;
    trace.selected_plan = selected.explain;
    trace.selected_plan_fingerprint = selected.fingerprint;
    trace.selected_plan_cost = selected_cost;
    trace.selected_plan_cost_breakdown = selected_cost_breakdown;
    trace.selected_plan_properties = selected.properties;
    trace.selected_plan_cardinality_estimates = selected.cardinality_estimates;
    trace.selected_plan_operator_counts = selected.operator_counts;
    trace.selected_plan_class_counts = selected.class_counts;
}

pub(super) fn record_logical_rewrite(
    report: &mut OptimizationSearchReport,
    rewrite: &LogicalRewriteOutput,
) {
    report.push_stage_event(rewrite.trace().clone());
    if let Some(warning) = rewrite.warning() {
        report.push_warning(warning);
    }
    for event in rewrite.events().iter().cloned() {
        report.push_rule_event(event);
    }
}

fn insert_logical_group(memo: &mut GraphMemo, logical: &LogicalPlan) -> GroupId {
    let expr = GroupExpr::from_logical(logical, memo);
    memo.insert_group(expr)
}

fn best_physical(
    memo: &GraphMemo,
    root: GroupId,
    catalog: &OptimizerCatalog,
    optimizer_context: &OptimizerContext,
    decisions: &mut Vec<String>,
    stage_events: &mut Vec<StageTrace>,
) -> PhysicalPlan {
    let group = memo.group(root).expect("memo group id should exist");
    group
        .first_expression()
        .expect("memo group should contain at least one expression")
        .to_physical(memo, catalog, optimizer_context, decisions, stage_events)
}

fn select_bounded_sort_plan(
    items: Vec<SortItem>,
    offset: usize,
    limit: usize,
    input: PhysicalPlan,
    catalog: &OptimizerCatalog,
    decisions: &mut Vec<String>,
) -> PhysicalPlan {
    if satisfies_ordering(&input, &items, catalog) {
        decisions.push("elide bounded sort: access path satisfies required ordering".to_string());
        return PhysicalPlan::LimitExec {
            offset,
            limit: Some(limit),
            input: Box::new(input),
        };
    }
    let top_n = PhysicalPlan::TopNExec {
        items: items.clone(),
        offset,
        limit,
        input: Box::new(input.clone()),
    };
    let sort_limit = PhysicalPlan::LimitExec {
        offset,
        limit: Some(limit),
        input: Box::new(PhysicalPlan::SortExec {
            items,
            input: Box::new(input),
        }),
    };
    let top_n_cost = estimate_physical_plan_cost(&top_n, catalog);
    let sort_limit_cost = estimate_physical_plan_cost(&sort_limit, catalog);
    if top_n_cost.cost < sort_limit_cost.cost {
        decisions.push(format!(
            "choose TopN for bounded sort: offset={offset} limit={limit} top_n_cost={} sort_limit_cost={}",
            top_n_cost.cost, sort_limit_cost.cost
        ));
        top_n
    } else {
        decisions.push(format!(
            "keep Sort + Limit for bounded sort: offset={offset} limit={limit} top_n_cost={} sort_limit_cost={}",
            top_n_cost.cost, sort_limit_cost.cost
        ));
        sort_limit
    }
}

fn stage_rule_counts(stage_events: &[StageTrace]) -> (usize, usize) {
    stage_events
        .iter()
        .fold((0, 0), |(applied, skipped), event| {
            let stats = event.stats();
            (
                applied.saturating_add(stats.applied_rules),
                skipped.saturating_add(stats.skipped_rules),
            )
        })
}

impl GroupExpr {
    fn from_logical(logical: &LogicalPlan, memo: &mut GraphMemo) -> Self {
        match logical {
            LogicalPlan::GraphMatch { input, .. } => Self {
                logical: logical.clone(),
                children: input
                    .iter()
                    .map(|input| insert_logical_group(memo, input))
                    .collect(),
            },
            LogicalPlan::CreateNodeLabel { .. }
            | LogicalPlan::CreateRelationshipType { .. }
            | LogicalPlan::CreateNodeTable { .. }
            | LogicalPlan::CreateRelationshipTable { .. }
            | LogicalPlan::CreateProperty { .. }
            | LogicalPlan::AlterTableState { .. }
            | LogicalPlan::AlterPropertyState { .. }
            | LogicalPlan::CreateIndex { .. }
            | LogicalPlan::CreateCompositeIndex { .. }
            | LogicalPlan::CreateRangeIndex { .. }
            | LogicalPlan::CreateFullTextIndex { .. }
            | LogicalPlan::CreateUniqueConstraint { .. }
            | LogicalPlan::CreateNodePropertyExistsConstraint { .. }
            | LogicalPlan::CreateRelationshipUniqueConstraint { .. }
            | LogicalPlan::CreateRelationshipPropertyExistsConstraint { .. }
            | LogicalPlan::ProjectGraph { .. }
            | LogicalPlan::GraphAlgorithm { .. }
            | LogicalPlan::GraphAlgorithmOutput(_)
            | LogicalPlan::VectorSeed { .. }
            | LogicalPlan::TextSeed { .. }
            | LogicalPlan::GraphSeed { .. }
            | LogicalPlan::CreateNode { .. }
            | LogicalPlan::UnwindMutation { .. }
            | LogicalPlan::MergeNode { .. }
            | LogicalPlan::MergeRelationship { .. }
            | LogicalPlan::MergeMatchedRelationship { .. }
            | LogicalPlan::MergeRelationshipFromMatchedRelationship { .. }
            | LogicalPlan::MergeRelationshipToMatchedTarget { .. }
            | LogicalPlan::MergeRelationshipFromMatchedTarget { .. }
            | LogicalPlan::CreateMatchedRelationship { .. }
            | LogicalPlan::SetNodeProperty { .. }
            | LogicalPlan::SetNodeProperties { .. }
            | LogicalPlan::SetNodePropertiesReturn { .. }
            | LogicalPlan::SetRelationshipProperty { .. }
            | LogicalPlan::SetRelationshipProperties { .. }
            | LogicalPlan::DeleteNode { .. }
            | LogicalPlan::DeleteRelationship { .. }
            | LogicalPlan::DeleteRelationshipTargetNodes { .. }
            | LogicalPlan::CreateRelationship { .. }
            | LogicalPlan::NodeScan { .. }
            | LogicalPlan::OptionalRelationshipCountSum { .. }
            | LogicalPlan::ThreadRepairStats { .. }
            | LogicalPlan::ShortestPath { .. } => Self {
                logical: logical.clone(),
                children: Vec::new(),
            },
            LogicalPlan::Limit { limit: Some(0), .. } => Self {
                logical: logical.clone(),
                children: Vec::new(),
            },
            LogicalPlan::NodeCartesianProduct { left, right } => Self {
                logical: logical.clone(),
                children: vec![
                    insert_logical_group(memo, left),
                    insert_logical_group(memo, right),
                ],
            },
            LogicalPlan::Limit {
                limit: Some(_),
                input,
                ..
            } if matches!(input.as_ref(), LogicalPlan::Sort { .. }) => {
                let LogicalPlan::Sort { input, .. } = input.as_ref() else {
                    unreachable!("guard requires a sort input");
                };
                Self {
                    logical: logical.clone(),
                    children: vec![insert_logical_group(memo, input)],
                }
            }
            LogicalPlan::Expand { input, .. }
            | LogicalPlan::NodeColumnLookup { input, .. }
            | LogicalPlan::OptionalDegree { input, .. }
            | LogicalPlan::Filter { input, .. }
            | LogicalPlan::Project { input, .. }
            | LogicalPlan::Aggregate { input, .. }
            | LogicalPlan::Distinct { input }
            | LogicalPlan::Sort { input, .. }
            | LogicalPlan::Limit { input, .. } => Self {
                logical: logical.clone(),
                children: vec![insert_logical_group(memo, input)],
            },
        }
    }

    fn to_physical(
        &self,
        memo: &GraphMemo,
        catalog: &OptimizerCatalog,
        optimizer_context: &OptimizerContext,
        decisions: &mut Vec<String>,
        stage_events: &mut Vec<StageTrace>,
    ) -> PhysicalPlan {
        lower_logical(
            &self.logical,
            LoweringChildren::Memo {
                memo,
                children: &self.children,
            },
            catalog,
            optimizer_context,
            decisions,
            stage_events,
        )
    }
}

fn push_seed_metadata_filter(
    input: &mut PhysicalPlan,
    predicate: &hawdb_plan_cypher::Predicate,
    decisions: &mut Vec<String>,
) {
    if let hawdb_plan_cypher::Predicate::And(predicates) = predicate {
        for predicate in predicates {
            push_seed_metadata_filter(input, predicate, decisions);
        }
        return;
    }
    let hawdb_plan_cypher::Predicate::PropertyEq {
        variable,
        property,
        value,
    } = predicate
    else {
        return;
    };
    let Some(filter_field) = seed_metadata_field(property) else {
        return;
    };
    let Some(filter_value) = seed_metadata_value(value) else {
        return;
    };
    let producer = seed_window(input)
        .map(|(producer, _)| producer)
        .unwrap_or("retriever");
    if attach_seed_metadata_filter(input, variable, filter_field, filter_value) {
        decisions.push(format!(
            "push descriptor-safe {producer} seed filter {variable}.{property} before candidate generation"
        ));
    }
}

fn attach_seed_metadata_filter(
    plan: &mut PhysicalPlan,
    variable: &str,
    field: &str,
    value: String,
) -> bool {
    match plan {
        PhysicalPlan::NodeColumnLookupExec {
            variable: lookup_variable,
            input,
            ..
        } if lookup_variable == variable => attach_metadata_filter_to_seed(input, field, value),
        PhysicalPlan::AdjacencyExpandExec {
            source_variable,
            input,
            ..
        } if source_variable == variable => {
            attach_seed_metadata_filter(input, variable, field, value)
        }
        _ => false,
    }
}

fn attach_metadata_filter_to_seed(plan: &mut PhysicalPlan, field: &str, value: String) -> bool {
    if let PhysicalPlan::TextSeedScan {
        metadata_filters, ..
    } = plan
    {
        if metadata_filters
            .get(field)
            .is_some_and(|existing| existing != &value)
        {
            return false;
        }
        metadata_filters.insert(field.to_string(), value);
        return true;
    }
    let PhysicalPlan::VectorSeedScan {
        metadata_filters,
        vector_plan,
        ..
    } = plan
    else {
        return false;
    };
    if metadata_filters
        .get(field)
        .is_some_and(|existing| existing != &value)
    {
        return false;
    }
    metadata_filters.insert(field.to_string(), value);
    attach_vector_filter_field(vector_plan, field);
    true
}

fn attach_vector_filter_field(plan: &mut hawdb_plan_cypher::VectorPhysicalPlan, field: &str) {
    match plan {
        hawdb_plan_cypher::VectorPhysicalPlan::Filter { fields } => {
            if !fields.iter().any(|existing| existing == field) {
                fields.push(field.to_string());
                fields.sort();
            }
        }
        hawdb_plan_cypher::VectorPhysicalPlan::VectorCandidateScan { input, .. }
        | hawdb_plan_cypher::VectorPhysicalPlan::ResidualFilter { input, .. }
        | hawdb_plan_cypher::VectorPhysicalPlan::RawVectorRerank { input, .. }
        | hawdb_plan_cypher::VectorPhysicalPlan::TopK { input, .. } => {
            attach_vector_filter_field(input, field);
        }
    }
}

fn seed_metadata_field(property: &str) -> Option<&str> {
    match property {
        "id" => Some("external_id"),
        "kind" | "external_id" | "source_id" | "space_id" | "unit_type" | "lifecycle_state"
        | "importance" | "confidence" | "created_at" | "updated_at" | "event_start"
        | "event_end" | "is_latest" => Some(property),
        _ => None,
    }
}

fn seed_metadata_value(value: &Value) -> Option<String> {
    match value {
        Value::String(value) => Some(value.clone()),
        Value::Bool(value) => Some(value.to_string()),
        Value::Int(value) => Some(value.to_string()),
        Value::Float(value) if value.is_finite() => Some(value.to_string()),
        Value::Uuid(value) => Some(value.to_string()),
        Value::Null | Value::Float(_) | Value::Binary(_) | Value::List(_) | Value::Map(_) => None,
    }
}

fn seed_window(plan: &PhysicalPlan) -> Option<(&'static str, usize)> {
    match plan {
        PhysicalPlan::VectorSeedScan { vector_plan, .. } => {
            vector_plan_top_k(vector_plan).map(|window| ("vector", window))
        }
        PhysicalPlan::TextSeedScan { top_k, .. } => Some(("text", *top_k)),
        PhysicalPlan::GraphSeedScan { top_k, .. } => Some(("graph", *top_k)),
        PhysicalPlan::NodeColumnLookupExec { input, .. }
        | PhysicalPlan::AdjacencyExpandExec { input, .. }
        | PhysicalPlan::AdjacencyExistsExec { input, .. }
        | PhysicalPlan::FilterExec { input, .. }
        | PhysicalPlan::ProjectExec { input, .. }
        | PhysicalPlan::LimitExec { input, .. } => seed_window(input),
        _ => None,
    }
}

fn vector_plan_top_k(plan: &hawdb_plan_cypher::VectorPhysicalPlan) -> Option<usize> {
    match plan {
        hawdb_plan_cypher::VectorPhysicalPlan::TopK { limit, .. } => Some(*limit),
        hawdb_plan_cypher::VectorPhysicalPlan::VectorCandidateScan { input, .. }
        | hawdb_plan_cypher::VectorPhysicalPlan::ResidualFilter { input, .. }
        | hawdb_plan_cypher::VectorPhysicalPlan::RawVectorRerank { input, .. } => {
            vector_plan_top_k(input)
        }
        hawdb_plan_cypher::VectorPhysicalPlan::Filter { .. } => None,
    }
}

fn logical_group_count(logical: &LogicalPlan) -> usize {
    match logical {
        LogicalPlan::GraphMatch { input, .. } => {
            1 + input.as_deref().map(logical_group_count).unwrap_or(0)
        }
        LogicalPlan::Limit { limit: Some(0), .. } => 1,
        LogicalPlan::Limit {
            limit: Some(_),
            input,
            ..
        } if matches!(input.as_ref(), LogicalPlan::Sort { .. }) => {
            let LogicalPlan::Sort { input, .. } = input.as_ref() else {
                unreachable!("guard requires a sort input");
            };
            // Bounded-sort selection owns the Sort; it is not a child group.
            1 + logical_group_count(input)
        }
        LogicalPlan::Expand { input, .. }
        | LogicalPlan::NodeColumnLookup { input, .. }
        | LogicalPlan::OptionalDegree { input, .. }
        | LogicalPlan::Filter { input, .. }
        | LogicalPlan::Project { input, .. }
        | LogicalPlan::Aggregate { input, .. }
        | LogicalPlan::Distinct { input }
        | LogicalPlan::Sort { input, .. }
        | LogicalPlan::Limit { input, .. } => 1 + logical_group_count(input),
        LogicalPlan::OptionalRelationshipCountSum { .. }
        | LogicalPlan::ThreadRepairStats { .. }
        | LogicalPlan::ShortestPath { .. } => 1,
        LogicalPlan::CreateNodeLabel { .. }
        | LogicalPlan::CreateRelationshipType { .. }
        | LogicalPlan::CreateNodeTable { .. }
        | LogicalPlan::CreateRelationshipTable { .. }
        | LogicalPlan::CreateProperty { .. }
        | LogicalPlan::AlterTableState { .. }
        | LogicalPlan::AlterPropertyState { .. }
        | LogicalPlan::CreateIndex { .. }
        | LogicalPlan::CreateCompositeIndex { .. }
        | LogicalPlan::CreateRangeIndex { .. }
        | LogicalPlan::CreateFullTextIndex { .. }
        | LogicalPlan::CreateUniqueConstraint { .. }
        | LogicalPlan::CreateNodePropertyExistsConstraint { .. }
        | LogicalPlan::CreateRelationshipUniqueConstraint { .. }
        | LogicalPlan::CreateRelationshipPropertyExistsConstraint { .. }
        | LogicalPlan::ProjectGraph { .. }
        | LogicalPlan::GraphAlgorithm { .. }
        | LogicalPlan::GraphAlgorithmOutput(_)
        | LogicalPlan::VectorSeed { .. }
        | LogicalPlan::TextSeed { .. }
        | LogicalPlan::GraphSeed { .. }
        | LogicalPlan::CreateNode { .. }
        | LogicalPlan::UnwindMutation { .. }
        | LogicalPlan::MergeNode { .. }
        | LogicalPlan::MergeRelationship { .. }
        | LogicalPlan::MergeMatchedRelationship { .. }
        | LogicalPlan::MergeRelationshipFromMatchedRelationship { .. }
        | LogicalPlan::MergeRelationshipToMatchedTarget { .. }
        | LogicalPlan::MergeRelationshipFromMatchedTarget { .. }
        | LogicalPlan::CreateMatchedRelationship { .. }
        | LogicalPlan::SetNodeProperty { .. }
        | LogicalPlan::SetNodeProperties { .. }
        | LogicalPlan::SetNodePropertiesReturn { .. }
        | LogicalPlan::SetRelationshipProperty { .. }
        | LogicalPlan::SetRelationshipProperties { .. }
        | LogicalPlan::DeleteNode { .. }
        | LogicalPlan::DeleteRelationship { .. }
        | LogicalPlan::DeleteRelationshipTargetNodes { .. }
        | LogicalPlan::CreateRelationship { .. }
        | LogicalPlan::NodeScan { .. } => 1,
        LogicalPlan::NodeCartesianProduct { left, right } => {
            1 + logical_group_count(left) + logical_group_count(right)
        }
    }
}

// The graph memo currently contains one expression per group. Only child
// lookup differs; physical alternatives and their costing share one lowerer.
enum LoweringChildren<'a> {
    Memo {
        memo: &'a GraphMemo,
        children: &'a [GroupId],
    },
    Direct,
}

impl LoweringChildren<'_> {
    fn lower(
        &self,
        logical: &LogicalPlan,
        index: usize,
        catalog: &OptimizerCatalog,
        optimizer_context: &OptimizerContext,
        decisions: &mut Vec<String>,
        stage_events: &mut Vec<StageTrace>,
    ) -> PhysicalPlan {
        match self {
            Self::Memo { memo, children } => best_physical(
                memo,
                children[index],
                catalog,
                optimizer_context,
                decisions,
                stage_events,
            ),
            Self::Direct => lower_logical(
                logical,
                Self::Direct,
                catalog,
                optimizer_context,
                decisions,
                stage_events,
            ),
        }
    }
}

fn lower_logical(
    logical: &LogicalPlan,
    children: LoweringChildren<'_>,
    catalog: &OptimizerCatalog,
    optimizer_context: &OptimizerContext,
    decisions: &mut Vec<String>,
    stage_events: &mut Vec<StageTrace>,
) -> PhysicalPlan {
    if let Some(plan) = select_exact_count_fast_path(logical, decisions, stage_events) {
        return plan;
    }
    if let Some(plan) = simple::lower_simple_logical(logical, optimizer_context) {
        return plan;
    }
    match logical {
        LogicalPlan::GraphMatch { program, input } => PhysicalPlan::GraphMatchExec {
            program: program.clone(),
            input: input.as_ref().map(|input| {
                Box::new(children.lower(
                    input,
                    0,
                    catalog,
                    optimizer_context,
                    decisions,
                    stage_events,
                ))
            }),
        },
        LogicalPlan::NodeCartesianProduct { left, right } => {
            let left = children.lower(left, 0, catalog, optimizer_context, decisions, stage_events);
            let right = children.lower(
                right,
                1,
                catalog,
                optimizer_context,
                decisions,
                stage_events,
            );
            let (left, right) =
                order_single_row_cartesian_product_children(catalog, decisions, left, right);
            push_cartesian_product_cost_decision(catalog, decisions, &left, &right);
            PhysicalPlan::NodeCartesianProductExec {
                left: Box::new(left),
                right: Box::new(right),
            }
        }
        LogicalPlan::NodeColumnLookup {
            variable,
            label,
            property,
            column,
            optional,
            node_visibility_predicate,
            input,
        } => PhysicalPlan::NodeColumnLookupExec {
            variable: variable.clone(),
            label: label.clone(),
            property: property.clone(),
            column: column.clone(),
            optional: *optional,
            node_visibility_predicate: node_visibility_predicate.clone(),
            input: Box::new(children.lower(
                input,
                0,
                catalog,
                optimizer_context,
                decisions,
                stage_events,
            )),
        },
        LogicalPlan::Expand {
            source_variable,
            source_label,
            rel_variable,
            rel_type,
            rel_properties,
            direction,
            target_variable,
            target_label,
            min_hops,
            max_hops,
            optional,
            input,
        } => {
            push_expand_estimate_decision(
                catalog,
                decisions,
                ExpandEstimateRequest {
                    source_label,
                    rel_type,
                    rel_properties,
                    target_label,
                    min_hops: *min_hops,
                    max_hops: *max_hops,
                },
            );
            let input = children.lower(
                input,
                0,
                catalog,
                optimizer_context,
                decisions,
                stage_events,
            );
            let graph_budget = seed_window(&input).map(|(producer, _)| {
                decisions.push(format!(
                    "admit {producer}-seeded graph expansion using execution memory budgets"
                ));
                // Keep seeded expansion reporting and admitted identity tracking.
                // Live ownership, not seed fanout or cumulative throughput, sets
                // the default resource boundary. Hosts may add explicit caps.
                GraphExpansionBudget {
                    candidate_limit: usize::MAX,
                    payload_byte_limit: usize::MAX,
                }
            });
            PhysicalPlan::AdjacencyExpandExec {
                source_variable: source_variable.clone(),
                source_label: source_label.clone(),
                rel_variable: rel_variable.clone(),
                rel_type: rel_type.clone(),
                rel_properties: rel_properties.clone(),
                direction: *direction,
                target_variable: target_variable.clone(),
                target_label: target_label.clone(),
                min_hops: *min_hops,
                max_hops: *max_hops,
                optional: *optional,
                graph_budget,
                input: Box::new(input),
            }
        }
        LogicalPlan::OptionalDegree {
            source_variable,
            rel_type,
            rel_properties,
            direction,
            target_label,
            target_properties,
            alias,
            input,
        } => PhysicalPlan::OptionalDegreeExec {
            source_variable: source_variable.clone(),
            rel_type: rel_type.clone(),
            rel_properties: rel_properties.clone(),
            direction: *direction,
            target_label: target_label.clone(),
            target_properties: target_properties.clone(),
            alias: alias.clone(),
            input: Box::new(children.lower(
                input,
                0,
                catalog,
                optimizer_context,
                decisions,
                stage_events,
            )),
        },
        LogicalPlan::OptionalRelationshipCountSum {
            variable,
            label,
            properties,
            legs,
            output,
        } => {
            push_optional_relationship_count_sum_cost_decision(
                catalog, decisions, label, properties, legs,
            );
            PhysicalPlan::OptionalRelationshipCountSumExec {
                variable: variable.clone(),
                label: label.clone(),
                properties: properties.clone(),
                legs: legs.clone(),
                output: output.clone(),
            }
        }
        LogicalPlan::Filter { predicate, input } => {
            if let Some(plan) =
                index_seek_from_filter(predicate, input, catalog, decisions, stage_events)
            {
                plan
            } else if let Some(plan) = access::source_segment_scan_from_filter(predicate, input) {
                decisions.push(
                    "choose SourceSegmentScan for storage-prunable Source filter".to_string(),
                );
                PhysicalPlan::FilterExec {
                    predicate: predicate.clone(),
                    input: Box::new(plan),
                }
            } else if let Predicate::BoundRelationshipExists {
                source_variable,
                rel_type,
                direction,
                target_variable,
            } = predicate
            {
                decisions.push(
                    "lower bound relationship existence predicate to AdjacencyExistsExec"
                        .to_string(),
                );
                PhysicalPlan::AdjacencyExistsExec {
                    source_variable: source_variable.clone(),
                    rel_type: rel_type.clone(),
                    direction: *direction,
                    target_variable: target_variable.clone(),
                    input: Box::new(children.lower(
                        input,
                        0,
                        catalog,
                        optimizer_context,
                        decisions,
                        stage_events,
                    )),
                }
            } else {
                let mut input = children.lower(
                    input,
                    0,
                    catalog,
                    optimizer_context,
                    decisions,
                    stage_events,
                );
                push_seed_metadata_filter(&mut input, predicate, decisions);
                input = join::lower_property_join(input, predicate, decisions);
                PhysicalPlan::FilterExec {
                    predicate: predicate.clone(),
                    input: Box::new(input),
                }
            }
        }
        LogicalPlan::Project { items, input } => PhysicalPlan::ProjectExec {
            items: items.clone(),
            input: Box::new(children.lower(
                input,
                0,
                catalog,
                optimizer_context,
                decisions,
                stage_events,
            )),
        },
        LogicalPlan::Aggregate {
            group_keys,
            items,
            input,
        } => PhysicalPlan::AggregateExec {
            group_keys: group_keys.clone(),
            items: items.clone(),
            input: Box::new(children.lower(
                input,
                0,
                catalog,
                optimizer_context,
                decisions,
                stage_events,
            )),
        },
        LogicalPlan::Distinct { input } => PhysicalPlan::DistinctExec {
            input: Box::new(children.lower(
                input,
                0,
                catalog,
                optimizer_context,
                decisions,
                stage_events,
            )),
        },
        LogicalPlan::Sort { items, input } => {
            let input = children.lower(
                input,
                0,
                catalog,
                optimizer_context,
                decisions,
                stage_events,
            );
            if satisfies_ordering(&input, items, catalog) {
                decisions
                    .push("elide SortExec: access path satisfies required ordering".to_string());
                input
            } else {
                PhysicalPlan::SortExec {
                    items: items.clone(),
                    input: Box::new(input),
                }
            }
        }
        LogicalPlan::Limit {
            offset,
            limit,
            input,
        } => {
            if *limit == Some(0) {
                PhysicalPlan::EmptyExec
            } else if let (Some(limit), LogicalPlan::Sort { items, input }) =
                (limit, input.as_ref())
            {
                let input = children.lower(
                    input,
                    0,
                    catalog,
                    optimizer_context,
                    decisions,
                    stage_events,
                );
                select_bounded_sort_plan(items.clone(), *offset, *limit, input, catalog, decisions)
            } else {
                PhysicalPlan::LimitExec {
                    offset: *offset,
                    limit: *limit,
                    input: Box::new(children.lower(
                        input,
                        0,
                        catalog,
                        optimizer_context,
                        decisions,
                        stage_events,
                    )),
                }
            }
        }
        _ => unreachable!("leaf logical plans are lowered before child planning"),
    }
}

fn select_exact_count_fast_path(
    logical: &LogicalPlan,
    decisions: &mut Vec<String>,
    stage_events: &mut Vec<StageTrace>,
) -> Option<PhysicalPlan> {
    if let Some(plan) = select_node_count_fast_path(logical, decisions, stage_events) {
        return Some(plan);
    }
    select_relationship_count_fast_path(logical, decisions, stage_events)
}

fn select_node_count_fast_path(
    logical: &LogicalPlan,
    decisions: &mut Vec<String>,
    stage_events: &mut Vec<StageTrace>,
) -> Option<PhysicalPlan> {
    let LogicalPlan::Aggregate {
        group_keys,
        items,
        input,
    } = logical
    else {
        return None;
    };
    let [item] = items.as_slice() else {
        return None;
    };
    let LogicalPlan::NodeScan { variable, label } = input.as_ref() else {
        return None;
    };
    let exact_node_count = group_keys.is_empty()
        && item.function == AggregateFunction::Count
        && match &item.target {
            AggregateTarget::All => !item.distinct,
            AggregateTarget::Variable(target) => target == variable,
            AggregateTarget::Property { .. }
            | AggregateTarget::Column(_)
            | AggregateTarget::ColumnProperty { .. } => false,
        };
    if !exact_node_count {
        return None;
    }

    decisions.push(format!(
        "selected implementation:node_count_fast_path: use exact label count for {label}"
    ));
    stage_events
        .push(ACCESS_PATH_SELECTION_STAGE.trace(StageStats::new(1, 1).with_rule_counts(1, 0)));
    Some(PhysicalPlan::NodeCountExec {
        label: label.clone(),
        output: item.name.clone(),
    })
}

fn select_relationship_count_fast_path(
    logical: &LogicalPlan,
    decisions: &mut Vec<String>,
    stage_events: &mut Vec<StageTrace>,
) -> Option<PhysicalPlan> {
    let LogicalPlan::Aggregate {
        group_keys,
        items,
        input,
    } = logical
    else {
        return None;
    };
    let [item] = items.as_slice() else {
        return None;
    };
    let LogicalPlan::Expand {
        source_variable,
        source_label,
        rel_variable,
        rel_type,
        rel_properties,
        direction,
        target_label,
        min_hops,
        max_hops,
        optional,
        input,
        ..
    } = input.as_ref()
    else {
        return None;
    };
    let LogicalPlan::NodeScan { variable, label } = input.as_ref() else {
        return None;
    };
    let exact_relationship_count = group_keys.is_empty()
        && item.function == AggregateFunction::Count
        && !item.distinct
        && source_variable == variable
        && source_label.is_empty()
        && label.is_empty()
        && target_label.is_empty()
        && rel_properties.is_empty()
        && *min_hops == 1
        && *max_hops == 1
        && !optional
        && matches!(
            direction,
            RelationshipDirection::Outgoing | RelationshipDirection::Incoming
        )
        && match &item.target {
            AggregateTarget::All => true,
            AggregateTarget::Variable(target) => rel_variable.as_ref() == Some(target),
            AggregateTarget::Property { .. }
            | AggregateTarget::Column(_)
            | AggregateTarget::ColumnProperty { .. } => false,
        };
    if !exact_relationship_count {
        return None;
    }

    decisions.push(format!(
        "selected implementation:relationship_count_fast_path: use exact relationship count for {rel_type}"
    ));
    stage_events
        .push(ACCESS_PATH_SELECTION_STAGE.trace(StageStats::new(1, 1).with_rule_counts(1, 0)));
    Some(PhysicalPlan::RelationshipCountExec {
        rel_type: rel_type.clone(),
        output: item.name.clone(),
    })
}

fn finalize_physical_plan(
    plan: PhysicalPlan,
    decisions: &mut Vec<String>,
    stage_events: &mut Vec<StageTrace>,
) -> PhysicalPlan {
    let event_count_before = stage_events.len();
    let finalized = finalize_required_node_properties(plan, decisions, stage_events);
    if !stage_events[event_count_before..]
        .iter()
        .any(|event| event.name() == PLAN_FINALIZATION_STAGE.name())
    {
        stage_events.push(PLAN_FINALIZATION_STAGE.trace(StageStats::new(1, 1)));
    }
    finalized
}

fn finalize_required_node_properties(
    plan: PhysicalPlan,
    decisions: &mut Vec<String>,
    stage_events: &mut Vec<StageTrace>,
) -> PhysicalPlan {
    match plan {
        PhysicalPlan::ProjectExec { items, input } => {
            select_node_projection_scan(&items, &input, decisions, stage_events)
                .unwrap_or(PhysicalPlan::ProjectExec { items, input })
        }
        PhysicalPlan::AggregateExec {
            group_keys,
            items,
            input,
        } => {
            let input = select_node_aggregate_required_scan(
                &group_keys,
                &items,
                &input,
                decisions,
                stage_events,
            )
            .map(Box::new)
            .unwrap_or(input);
            PhysicalPlan::AggregateExec {
                group_keys,
                items,
                input,
            }
        }
        PhysicalPlan::LimitExec {
            offset,
            limit,
            input,
        } => PhysicalPlan::LimitExec {
            offset,
            limit,
            input: Box::new(finalize_required_node_properties(
                *input,
                decisions,
                stage_events,
            )),
        },
        PhysicalPlan::DistinctExec { input } => PhysicalPlan::DistinctExec {
            input: Box::new(finalize_required_node_properties(
                *input,
                decisions,
                stage_events,
            )),
        },
        PhysicalPlan::SortExec { items, input }
            if sort_items_use_only_projected_columns(&items) =>
        {
            PhysicalPlan::SortExec {
                items,
                input: Box::new(finalize_required_node_properties(
                    *input,
                    decisions,
                    stage_events,
                )),
            }
        }
        PhysicalPlan::TopNExec {
            items,
            offset,
            limit,
            input,
        } if sort_items_use_only_projected_columns(&items) => PhysicalPlan::TopNExec {
            items,
            offset,
            limit,
            input: Box::new(finalize_required_node_properties(
                *input,
                decisions,
                stage_events,
            )),
        },
        plan => plan,
    }
}

fn sort_items_use_only_projected_columns(items: &[SortItem]) -> bool {
    items
        .iter()
        .all(|item| matches!(item.key, SortKey::Column(_)))
}

fn select_node_projection_scan(
    items: &[Projection],
    input: &PhysicalPlan,
    decisions: &mut Vec<String>,
    stage_events: &mut Vec<StageTrace>,
) -> Option<PhysicalPlan> {
    let (source, predicate) = match input {
        PhysicalPlan::FilterExec { predicate, input } => (input.as_ref(), Some(predicate)),
        source => (source, None),
    };
    let (variable, label, access) = node_projection_access(source)?;
    let mut required_properties = BTreeSet::new();
    if !items.iter().all(|item| {
        collect_projection_properties(&item.expression, variable, &mut required_properties)
    }) || predicate.is_some_and(|predicate| {
        !collect_predicate_properties(predicate, variable, &mut required_properties)
    }) {
        return None;
    }
    collect_access_properties(&access, &mut required_properties);

    let required_properties = required_properties.into_iter().collect::<Vec<_>>();
    decisions.push(format!(
        "selected implementation:node_projection_scan: access={} decode {} required properties for {variable}:{label}",
        access.kind_name(),
        required_properties.len(),
    ));
    stage_events.push(PLAN_FINALIZATION_STAGE.trace(StageStats::new(1, 1).with_rule_counts(1, 0)));
    Some(PhysicalPlan::NodeProjectionScanExec {
        variable: variable.clone(),
        label: label.clone(),
        access,
        required_properties,
        predicate: predicate.cloned(),
        items: items.to_vec(),
    })
}

fn select_node_aggregate_required_scan(
    group_keys: &[Projection],
    items: &[hawdb_plan_cypher::Aggregation],
    input: &PhysicalPlan,
    decisions: &mut Vec<String>,
    stage_events: &mut Vec<StageTrace>,
) -> Option<PhysicalPlan> {
    let (source, predicate) = match input {
        PhysicalPlan::FilterExec { predicate, input } => (input.as_ref(), Some(predicate)),
        source => (source, None),
    };
    let (variable, label, access) = node_projection_access(source)?;
    let mut required_properties = BTreeSet::new();
    if !group_keys.iter().all(|item| {
        collect_projection_properties(&item.expression, variable, &mut required_properties)
    }) || !items
        .iter()
        .all(|item| collect_aggregate_properties(item, variable, &mut required_properties))
        || predicate.is_some_and(|predicate| {
            !collect_predicate_properties(predicate, variable, &mut required_properties)
        })
    {
        return None;
    }
    collect_access_properties(&access, &mut required_properties);

    let required_properties = required_properties.into_iter().collect::<Vec<_>>();
    decisions.push(format!(
        "selected implementation:node_aggregate_required_scan: access={} decode {} required properties for {variable}:{label}",
        access.kind_name(),
        required_properties.len(),
    ));
    stage_events.push(PLAN_FINALIZATION_STAGE.trace(StageStats::new(1, 1).with_rule_counts(1, 0)));
    Some(PhysicalPlan::NodeProjectionScanExec {
        variable: variable.clone(),
        label: label.clone(),
        access,
        required_properties,
        predicate: predicate.cloned(),
        items: Vec::new(),
    })
}

fn collect_aggregate_properties(
    item: &hawdb_plan_cypher::Aggregation,
    variable: &str,
    required: &mut BTreeSet<String>,
) -> bool {
    match (&item.function, &item.target) {
        (AggregateFunction::Count, AggregateTarget::All) => true,
        (AggregateFunction::Count, AggregateTarget::Variable(current)) => current == variable,
        (
            AggregateFunction::Count
            | AggregateFunction::Min
            | AggregateFunction::Max
            | AggregateFunction::Avg
            | AggregateFunction::Collect,
            AggregateTarget::Property {
                variable: current,
                property,
            },
        ) if current == variable => {
            required.insert(property.clone());
            true
        }
        _ => false,
    }
}

fn node_projection_access(plan: &PhysicalPlan) -> Option<(&String, &String, NodeProjectionAccess)> {
    match plan {
        PhysicalPlan::SeqNodeScan { variable, label } => {
            Some((variable, label, NodeProjectionAccess::LabelScan))
        }
        PhysicalPlan::IndexNodeSeek {
            variable,
            label,
            property,
            value,
        } => Some((
            variable,
            label,
            NodeProjectionAccess::PropertyValues {
                property: property.clone(),
                values: vec![value.clone()],
            },
        )),
        PhysicalPlan::IndexNodeMultiSeek {
            variable,
            label,
            property,
            values,
        } => Some((
            variable,
            label,
            NodeProjectionAccess::PropertyValues {
                property: property.clone(),
                values: values.clone(),
            },
        )),
        PhysicalPlan::IndexNodeUnionSeek {
            variable,
            label,
            branches,
        } => Some((
            variable,
            label,
            NodeProjectionAccess::PropertyUnion {
                branches: branches.clone(),
            },
        )),
        PhysicalPlan::IndexNodeCompositeSeek {
            variable,
            label,
            predicates,
        } => Some((
            variable,
            label,
            NodeProjectionAccess::CompositeEquality {
                predicates: predicates.clone(),
            },
        )),
        PhysicalPlan::IndexNodeCompositeRangeSeek {
            variable,
            label,
            seek,
        } => Some((
            variable,
            label,
            NodeProjectionAccess::CompositeRange { seek: seek.clone() },
        )),
        PhysicalPlan::IndexNodeRangeSeek {
            variable,
            label,
            property,
            lower,
            upper,
        } => Some((
            variable,
            label,
            NodeProjectionAccess::PropertyRange {
                property: property.clone(),
                lower: lower.clone(),
                upper: upper.clone(),
            },
        )),
        PhysicalPlan::IndexNodeTextSeek {
            variable,
            label,
            property,
            query,
        } => Some((
            variable,
            label,
            NodeProjectionAccess::FullText {
                property: property.clone(),
                query: query.clone(),
            },
        )),
        _ => None,
    }
}

fn collect_access_properties(access: &NodeProjectionAccess, required: &mut BTreeSet<String>) {
    match access {
        NodeProjectionAccess::LabelScan => {}
        NodeProjectionAccess::PropertyValues { property, .. }
        | NodeProjectionAccess::PropertyRange { property, .. }
        | NodeProjectionAccess::FullText { property, .. } => {
            required.insert(property.clone());
        }
        NodeProjectionAccess::CompositeEquality { predicates } => {
            required.extend(predicates.iter().map(|(property, _)| property.clone()));
        }
        NodeProjectionAccess::CompositeRange { seek } => {
            required.extend(
                seek.equality_prefix
                    .iter()
                    .map(|(property, _)| property.clone()),
            );
            required.insert(seek.range_property.clone());
        }
        NodeProjectionAccess::PropertyUnion { branches } => {
            required.extend(branches.iter().map(|branch| branch.property.clone()));
        }
    }
}

fn collect_predicate_properties(
    predicate: &Predicate,
    variable: &str,
    required: &mut BTreeSet<String>,
) -> bool {
    match predicate {
        Predicate::And(predicates) | Predicate::Or(predicates) => predicates
            .iter()
            .all(|predicate| collect_predicate_properties(predicate, variable, required)),
        Predicate::Not(predicate) => collect_predicate_properties(predicate, variable, required),
        Predicate::ConstantBool(_) => true,
        Predicate::IdEq {
            variable: current, ..
        }
        | Predicate::IdNotEq {
            variable: current, ..
        }
        | Predicate::IdCompare {
            variable: current, ..
        }
        | Predicate::IdIn {
            variable: current, ..
        } => current == variable,
        Predicate::PropertyEq {
            variable: current,
            property,
            ..
        }
        | Predicate::PropertyNotEq {
            variable: current,
            property,
            ..
        }
        | Predicate::PropertyCompare {
            variable: current,
            property,
            ..
        }
        | Predicate::PropertyListContains {
            variable: current,
            property,
            ..
        }
        | Predicate::PropertyListContainsLower {
            variable: current,
            property,
            ..
        }
        | Predicate::PropertyContains {
            variable: current,
            property,
            ..
        }
        | Predicate::PropertyStartsWith {
            variable: current,
            property,
            ..
        }
        | Predicate::PropertyEndsWith {
            variable: current,
            property,
            ..
        }
        | Predicate::PropertyRegexMatch {
            variable: current,
            property,
            ..
        }
        | Predicate::PropertyIsNull {
            variable: current,
            property,
        }
        | Predicate::PropertyIsNotNull {
            variable: current,
            property,
        }
        | Predicate::PropertyIn {
            variable: current,
            property,
            ..
        } => {
            if current != variable {
                return false;
            }
            required.insert(property.clone());
            true
        }
        Predicate::ExpressionEq { expression, value }
        | Predicate::ExpressionNotEq { expression, value }
        | Predicate::ExpressionContains { expression, value } => {
            collect_projection_properties(expression, variable, required)
                && collect_projection_properties(value, variable, required)
        }
        Predicate::ExpressionIn { expression, .. } => {
            collect_projection_properties(expression, variable, required)
        }
        Predicate::ExpressionCompare {
            expression, value, ..
        } => {
            collect_projection_properties(expression, variable, required)
                && collect_projection_properties(value, variable, required)
        }
        Predicate::RelationshipExists { .. } | Predicate::BoundRelationshipExists { .. } => false,
    }
}

fn collect_projection_properties(
    expression: &ProjectionExpression,
    variable: &str,
    required: &mut BTreeSet<String>,
) -> bool {
    match expression {
        ProjectionExpression::Case { .. }
        | ProjectionExpression::Binary { .. }
        | ProjectionExpression::Not(_)
        | ProjectionExpression::IsNull { .. } => expression
            .all_children(|child| collect_projection_properties(child, variable, required)),
        ProjectionExpression::Variable { .. }
        | ProjectionExpression::RelationshipType { .. }
        | ProjectionExpression::Column(_)
        | ProjectionExpression::ColumnProperty { .. }
        | ProjectionExpression::ColumnDefaultIfNullOrEq { .. }
        | ProjectionExpression::ColumnValueDefaultIfNull { .. }
        | ProjectionExpression::ColumnValueCasePropertyNotNullOrEq { .. }
        | ProjectionExpression::CaseColumnSearchRank(_) => false,
        ProjectionExpression::Id { variable: current } => current == variable,
        ProjectionExpression::Literal(_) => true,
        ProjectionExpression::Property {
            variable: current,
            property,
        }
        | ProjectionExpression::DatePart {
            variable: current,
            property,
            ..
        }
        | ProjectionExpression::DefaultIfNullOrEq {
            variable: current,
            property,
            ..
        }
        | ProjectionExpression::DefaultIfNull {
            variable: current,
            property,
            ..
        }
        | ProjectionExpression::CasePropertyNotNullOrEq {
            variable: current,
            property,
            ..
        }
        | ProjectionExpression::CasePropertyEqualsRank {
            variable: current,
            property,
            ..
        }
        | ProjectionExpression::CaseLowerPropertyDefault {
            variable: current,
            property,
            ..
        } => {
            if current != variable {
                return false;
            }
            required.insert(property.clone());
            true
        }
        ProjectionExpression::Coalesce(expressions) => expressions
            .iter()
            .all(|expression| collect_projection_properties(expression, variable, required)),
        ProjectionExpression::Left { expression, .. }
        | ProjectionExpression::Lower(expression)
        | ProjectionExpression::JsonValue { expression, .. } => {
            collect_projection_properties(expression, variable, required)
        }
        ProjectionExpression::CaseCoalesceDifferenceFloorZero {
            variable: current,
            terms,
        } => {
            if current != variable {
                return false;
            }
            required.extend(terms.iter().map(|term| term.property.clone()));
            true
        }
        ProjectionExpression::CaseEntitySearchRank(rank) => {
            if rank.variable != variable {
                return false;
            }
            required.insert(rank.name_property.clone());
            required.insert(rank.aliases_property.clone());
            true
        }
    }
}

struct ExpandEstimateRequest<'a> {
    source_label: &'a str,
    rel_type: &'a str,
    rel_properties: &'a BTreeMap<String, Value>,
    target_label: &'a str,
    min_hops: usize,
    max_hops: usize,
}

fn push_expand_estimate_decision(
    catalog: &OptimizerCatalog,
    decisions: &mut Vec<String>,
    request: ExpandEstimateRequest<'_>,
) {
    let estimate = catalog.estimate_expand_rows(
        request.source_label,
        request.rel_type,
        request.rel_properties,
        request.target_label,
        request.min_hops,
        request.max_hops,
    );
    let path_count = estimate
        .path_count
        .map(|count| count.to_string())
        .unwrap_or_else(|| "unknown".to_string());
    let hop_rows = estimate
        .hop_estimates
        .iter()
        .map(|estimate| {
            format!(
                "{}:{}:{}",
                estimate.hop,
                if estimate.exact { "exact" } else { "fallback" },
                estimate.rows
            )
        })
        .collect::<Vec<_>>()
        .join(",");
    decisions.push(format!(
        "estimate AdjacencyExpand for {}-[:{}*{}..{}]->{}: path_count={path_count} rel_count={} rel_type_sources={} average_fanout={} rel_property_distinct_product={} hop_rows=[{}] estimated_rows={}",
        request.source_label,
        request.rel_type,
        request.min_hops,
        request.max_hops,
        request.target_label,
        estimate.rel_count,
        estimate.source_count,
        estimate.average_fanout,
        estimate.property_distinct_product,
        hop_rows,
        estimate.estimated_rows
    ));
}

fn order_single_row_cartesian_product_children(
    catalog: &OptimizerCatalog,
    decisions: &mut Vec<String>,
    left: PhysicalPlan,
    right: PhysicalPlan,
) -> (PhysicalPlan, PhysicalPlan) {
    let left_cost = estimate_physical_plan_cost(&left, catalog);
    let right_cost = estimate_physical_plan_cost(&right, catalog);
    if !cartesian_product_leaves_are_single_row(catalog, &left)
        || !cartesian_product_leaves_are_single_row(catalog, &right)
    {
        decisions.push(format!(
            "keep NodeCartesianProduct input order: left_rows={} right_rows={} reason=non_single_row_input",
            left_cost.estimated_rows, right_cost.estimated_rows
        ));
        return (left, right);
    }

    let mut leaves = Vec::new();
    collect_cartesian_product_leaves(left, &mut leaves);
    collect_cartesian_product_leaves(right, &mut leaves);

    let mut keyed_leaves = leaves
        .into_iter()
        .map(|plan| {
            let cost = estimate_physical_plan_cost(&plan, catalog);
            let fingerprint = plan.instance_fingerprint();
            (cost, fingerprint, plan)
        })
        .collect::<Vec<_>>();

    let original_order = keyed_leaves
        .iter()
        .map(|(cost, fingerprint, _)| format!("{}:{}", cost.cost, fingerprint))
        .collect::<Vec<_>>()
        .join("|");
    keyed_leaves.sort_by(
        |(left_cost, left_fingerprint, _), (right_cost, right_fingerprint, _)| {
            (left_cost.cost, left_fingerprint).cmp(&(right_cost.cost, right_fingerprint))
        },
    );
    let ordered = keyed_leaves
        .iter()
        .map(|(cost, fingerprint, _)| format!("{}:{}", cost.cost, fingerprint))
        .collect::<Vec<_>>()
        .join("|");
    if original_order == ordered {
        decisions.push(format!(
            "keep NodeCartesianProduct single-row input order: inputs={} order={ordered}",
            keyed_leaves.len()
        ));
    } else {
        decisions.push(format!(
            "order NodeCartesianProduct single-row inputs: inputs={} original={original_order} ordered={ordered}",
            keyed_leaves.len()
        ));
    }

    let mut ordered_plans = keyed_leaves.into_iter().map(|(_, _, plan)| plan);
    let left = ordered_plans
        .next()
        .expect("cartesian product has left input");
    let right = rebuild_cartesian_product(ordered_plans);
    (left, right)
}

fn cartesian_product_leaves_are_single_row(
    catalog: &OptimizerCatalog,
    plan: &PhysicalPlan,
) -> bool {
    match plan {
        PhysicalPlan::NodeCartesianProductExec { left, right } => {
            cartesian_product_leaves_are_single_row(catalog, left)
                && cartesian_product_leaves_are_single_row(catalog, right)
        }
        plan => estimate_physical_plan_cost(plan, catalog).estimated_rows == 1,
    }
}

fn collect_cartesian_product_leaves(plan: PhysicalPlan, leaves: &mut Vec<PhysicalPlan>) {
    match plan {
        PhysicalPlan::NodeCartesianProductExec { left, right } => {
            collect_cartesian_product_leaves(*left, leaves);
            collect_cartesian_product_leaves(*right, leaves);
        }
        plan => leaves.push(plan),
    }
}

fn rebuild_cartesian_product(plans: impl IntoIterator<Item = PhysicalPlan>) -> PhysicalPlan {
    let mut plans = plans.into_iter();
    let first = plans
        .next()
        .expect("cartesian product rebuild requires at least one input");
    plans.fold(first, |left, right| {
        PhysicalPlan::NodeCartesianProductExec {
            left: Box::new(left),
            right: Box::new(right),
        }
    })
}

fn push_cartesian_product_cost_decision(
    catalog: &OptimizerCatalog,
    decisions: &mut Vec<String>,
    left: &PhysicalPlan,
    right: &PhysicalPlan,
) {
    let left_cost = estimate_physical_plan_cost(left, catalog);
    let right_cost = estimate_physical_plan_cost(right, catalog);
    let cost = estimate_node_cartesian_product_cost(left_cost, right_cost);
    decisions.push(format!(
        "estimate NodeCartesianProduct: left_rows={} right_rows={} output_rows={} left_cost={} right_cost={} cost={}",
        left_cost.estimated_rows,
        right_cost.estimated_rows,
        cost.estimated_rows,
        left_cost.cost,
        right_cost.cost,
        cost.cost
    ));
}