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Detect-and-bail guard for the join_order heuristic in cyclic join queries #23

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Detect-and-bail guard for the join_order heuristic in cyclic join queries #23

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adfed2f
add detect-and-bail guard for cyclic join queries
jianhongshi123 Aug 5, 2026
58941c9
fix incorrect cyclic join test
jianhongshi123 Aug 5, 2026
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40 changes: 40 additions & 0 deletions src/optimizer/robust_optimizer.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -796,6 +796,42 @@ vector<PhysicalDAGNode *> RobustOptimizerContextState::BuildPhysicalPlanDAG(Logi
return all_nodes;
}

bool ExistCycle(vector<PhysicalDAGNode *> &all_nodes) {
unordered_map<idx_t, bool> visited;
for (auto *node : all_nodes) {
if (visited.count(node->table_idx)) {
continue;
}
idx_t cntNodes = 0;
idx_t cntEdges = 0;
vector<PhysicalDAGNode *> que;
auto discover = [&](PhysicalDAGNode *candidate) {
if (visited.count(candidate->table_idx)) {
return;
}
visited[candidate->table_idx] = true;
que.push_back(candidate);
cntNodes++;
cntEdges += candidate->parents.size() + candidate->children.size();
};
discover(node);
while (!que.empty()) {
auto cur = que.back();
que.pop_back();
for (auto &child : cur->children) {
discover(child);
}
for (auto &parent : cur->parents) {
discover(parent);
}
}
if (cntEdges / 2 >= cntNodes) {
return true;
}
}
return false;
}

void RobustOptimizerContextState::FlipRootsToLeaves(vector<PhysicalDAGNode *> &all_nodes) {
// step 1: find all roots
vector<PhysicalDAGNode *> roots;
Expand Down Expand Up @@ -1679,6 +1715,10 @@ unique_ptr<LogicalOperator> RobustOptimizerContextState::Optimize(unique_ptr<Log
map<ColKey, ColKey> uf_parent;
auto all_nodes = BuildPhysicalPlanDAG(plan.get(), uf_parent);

if (ExistCycle(all_nodes)) {
D_PRINTF("Cycle Detected");
return plan;
}
// flip non-largest roots to leaves (default: on)
Value flip_val;
bool flip_roots = true;
Expand Down
21 changes: 1 addition & 20 deletions test/sql/plan_positive.test
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Expand Up @@ -84,26 +84,7 @@ WHERE t1.k12 = t2.k12
----
physical_plan <REGEX>:.*PROBE_FILTER.*

# Correctness: triangle join
query II
EXPLAIN SELECT count(*)
FROM t2, t3, t4
WHERE t2.k23 = t3.k23
AND t3.k34 = t4.k34
AND t2.k24 = t4.k24;
----
physical_plan <REGEX>:.*CREATE_FILTER.*

query II
EXPLAIN SELECT count(*)
FROM t2, t3, t4
WHERE t2.k23 = t3.k23
AND t3.k34 = t4.k34
AND t2.k24 = t4.k24;
----
physical_plan <REGEX>:.*PROBE_FILTER.*

# Negative: four-table chain join
# Positive: four-table chain join
query II
EXPLAIN SELECT count(*)
FROM t1, t2, t3, t4
Expand Down
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