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[feature] use bit mask to avoid potential stack over flow if DFS #5

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[feature] use bit mask to avoid potential stack over flow if DFS #5

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54 changes: 42 additions & 12 deletions src/main/java/simpledb/optimizer/JoinOptimizer.java
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Original file line number Diff line number Diff line change
Expand Up @@ -239,6 +239,30 @@ private <T> void subsetDfs(final Set<Set<T>> result, final Set<T> path, final Li
}
}

public <T> HashMap<Integer, Set<Set<T>>> buildMap(List<T> v) {
final HashMap<Integer, Set<Set<T>>> result = new HashMap<>();
int n = v.size();
int state = 0;
while(state < (1 << n)){
Set<T> cur = new HashSet<>();
for(int j = 0; j < n; j ++ ){
if(((state >> j) & 1) == 1){
cur.add(v.get(j));
}
}
int count = Integer.bitCount(state);
if(result.containsKey(count)){
result.get(count).add(cur);
}else{
Set<Set<T>> value = new HashSet<>();
value.add(cur);
result.put(count, value);
}
state ++ ;
}
return result;
}

/**
* Compute a logical, reasonably efficient join on the specified tables. See
* PS4 for hints on how this should be implemented.
Expand All @@ -259,24 +283,30 @@ private <T> void subsetDfs(final Set<Set<T>> result, final Set<T> path, final Li
* when stats or filter selectivities is missing a table in the
* join, or or when another internal error occurs
*/
public List<LogicalJoinNode> orderJoins(Map<String, TableStats> stats, Map<String, Double> filterSelectivities,
boolean explain) throws ParsingException {
final PlanCache pc = new PlanCache();
public List<LogicalJoinNode> orderJoins(
Map<String, TableStats> stats,
Map<String, Double> filterSelectivities, boolean explain)
throws ParsingException {

PlanCache pc = new PlanCache();
int n = this.joins.size();

CostCard costCard = null;
for (int i = 1; i <= this.joins.size(); i++) {
final Set<Set<LogicalJoinNode>> subsets = enumerateSubsets(this.joins, i);
for (final Set<LogicalJoinNode> subPlan : subsets) {
HashMap<Integer, Set<Set<LogicalJoinNode>>> sizeToJoins = buildMap(this.joins);
for(int i = 1; i <= n; i ++ ){
Set<Set<LogicalJoinNode>> sets = sizeToJoins.get(i);
for(Set<LogicalJoinNode> subset: sets){
double bestCost = Double.MAX_VALUE;
for (final LogicalJoinNode removeNode : subPlan) {
final CostCard cc = computeCostAndCardOfSubplan(stats, filterSelectivities, removeNode, subPlan,
bestCost, pc);
if (cc != null) {
for(LogicalJoinNode removedNode: subset){
final CostCard cc = computeCostAndCardOfSubplan(stats, filterSelectivities, removedNode, subset,
bestCost, pc);
if(cc != null){
bestCost = cc.cost;
costCard = cc;
}
}
if (bestCost != Double.MAX_VALUE) {
pc.addPlan(subPlan, bestCost, costCard.card, costCard.plan);
if(bestCost != Double.MAX_VALUE){
pc.addPlan(subset, bestCost, costCard.card, costCard.plan);
}
}
}
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