/**
* This is a helper method that computes the cost and cardinality of joining joinToRemove to
* joinSet (joinSet should contain joinToRemove), given that all of the subsets of size
* joinSet.size() - 1 have already been computed and stored in PlanCache pc.
*
* @param stats table stats for all of the tables, referenced by table names rather than alias
* (see {@link #orderJoins})
* @param filterSelectivities the selectivities of the filters over each of the tables (where
* tables are indentified by their alias or name if no alias is given)
* @param joinToRemove the join to remove from joinSet
* @param joinSet the set of joins being considered
* @param bestCostSoFar the best way to join joinSet so far (minimum of previous invocations of
* computeCostAndCardOfSubplan for this joinSet, from returned CostCard)
* @param pc the PlanCache for this join; should have subplans for all plans of size
* joinSet.size()-1
* @return A {@link CostCard} objects desribing the cost, cardinality, optimal subplan
* @throws ParsingException when stats, filterSelectivities, or pc object is missing tables
* involved in join
*/
@SuppressWarnings("unchecked")
private CostCard computeCostAndCardOfSubplan(
HashMap<String, TableStats> stats,
HashMap<String, Double> filterSelectivities,
LogicalJoinNode joinToRemove,
Set<LogicalJoinNode> joinSet,
double bestCostSoFar,
PlanCache pc)
throws ParsingException {
LogicalJoinNode j = joinToRemove;
Vector<LogicalJoinNode> prevBest;
if (this.p.getTableId(j.t1Alias) == null)
throw new ParsingException("Unknown table " + j.t1Alias);
if (this.p.getTableId(j.t2Alias) == null)
throw new ParsingException("Unknown table " + j.t2Alias);
String table1Name = Database.getCatalog().getTableName(this.p.getTableId(j.t1Alias));
String table2Name = Database.getCatalog().getTableName(this.p.getTableId(j.t2Alias));
String table1Alias = j.t1Alias;
String table2Alias = j.t2Alias;
Set<LogicalJoinNode> news = (Set<LogicalJoinNode>) ((HashSet<LogicalJoinNode>) joinSet).clone();
news.remove(j);
double t1cost, t2cost;
int t1card, t2card;
boolean leftPkey, rightPkey;
if (news.isEmpty()) { // base case -- both are base relations
prevBest = new Vector<LogicalJoinNode>();
t1cost = stats.get(table1Name).estimateScanCost();
t1card = stats.get(table1Name).estimateTableCardinality(filterSelectivities.get(j.t1Alias));
leftPkey = isPkey(j.t1Alias, j.f1PureName);
t2cost = table2Alias == null ? 0 : stats.get(table2Name).estimateScanCost();
t2card =
table2Alias == null
? 0
: stats.get(table2Name).estimateTableCardinality(filterSelectivities.get(j.t2Alias));
rightPkey = table2Alias == null ? false : isPkey(table2Alias, j.f2PureName);
} else {
// news is not empty -- figure best way to join j to news
prevBest = pc.getOrder(news);
// possible that we have not cached an answer, if subset
// includes a cross product
if (prevBest == null) {
return null;
}
double prevBestCost = pc.getCost(news);
int bestCard = pc.getCard(news);
// estimate cost of right subtree
if (doesJoin(prevBest, table1Alias)) { // j.t1 is in prevBest
t1cost = prevBestCost; // left side just has cost of whatever
// left
// subtree is
t1card = bestCard;
leftPkey = hasPkey(prevBest);
t2cost = j.t2Alias == null ? 0 : stats.get(table2Name).estimateScanCost();
t2card =
j.t2Alias == null
? 0
: stats
.get(table2Name)
.estimateTableCardinality(filterSelectivities.get(j.t2Alias));
rightPkey = j.t2Alias == null ? false : isPkey(j.t2Alias, j.f2PureName);
} else if (doesJoin(prevBest, j.t2Alias)) { // j.t2 is in prevbest
// (both
// shouldn't be)
t2cost = prevBestCost; // left side just has cost of whatever
// left
// subtree is
t2card = bestCard;
rightPkey = hasPkey(prevBest);
t1cost = stats.get(table1Name).estimateScanCost();
t1card = stats.get(table1Name).estimateTableCardinality(filterSelectivities.get(j.t1Alias));
leftPkey = isPkey(j.t1Alias, j.f1PureName);
} else {
// don't consider this plan if one of j.t1 or j.t2
// isn't a table joined in prevBest (cross product)
return null;
}
}
// case where prevbest is left
double cost1 = estimateJoinCost(j, t1card, t2card, t1cost, t2cost);
LogicalJoinNode j2 = j.swapInnerOuter();
double cost2 = estimateJoinCost(j2, t2card, t1card, t2cost, t1cost);
if (cost2 < cost1) {
boolean tmp;
j = j2;
cost1 = cost2;
tmp = rightPkey;
rightPkey = leftPkey;
leftPkey = tmp;
}
if (cost1 >= bestCostSoFar) return null;
CostCard cc = new CostCard();
cc.card = estimateJoinCardinality(j, t1card, t2card, leftPkey, rightPkey, stats);
cc.cost = cost1;
cc.plan = (Vector<LogicalJoinNode>) prevBest.clone();
cc.plan.addElement(j); // prevbest is left -- add new join to end
return cc;
}
/**
* This is a helper method that computes the cost and cardinality of joining a LogicalJoinNode j
* to the current greedy plan we have built up.
*
* @param j the join to try adding to our plan
* @param plan the current plan we have built so far from the greedy algorithm, a Vector of
* LogicalJoinNodes that we've so far chosen.
* @param planCardinalities given the join order from plan, we also keep track of how large joined
* tables are, so we can help estimate the cardinality and cost of this next join
* @param planCosts given the join order from plan, we also keep track of how expensive executing
* some joins are, so we can help estimate the cardinality and cost of this next join
* @param stats table stats for all of the tables, referenced by table names rather than alias
* (see {@link #orderGreedyJoins(HashMap, HashMap)})
* @param filterSelectivities the selectivities of the filters over each of the tables (where
* tables are indentified by their alias or name if no alias is given)
* @return A {@link CostCard} objects desribing the cost, cardinality, optimal subplan
* @throws ParsingException when stats, filterSelectivities, or pc object is missing tables
* involved in join
*/
private CostCard costGreedyJoin(
LogicalJoinNode j,
Vector<LogicalJoinNode> plan,
Vector<Integer> planCardinalities,
Vector<Double> planCosts,
HashMap<String, TableStats> stats,
HashMap<String, Double> filterSelectivities)
throws ParsingException {
if (this.p.getTableId(j.t1Alias) == null)
throw new ParsingException("Unknown table " + j.t1Alias);
if (this.p.getTableId(j.t2Alias) == null)
throw new ParsingException("Unknown table " + j.t2Alias);
String table1Name = Database.getCatalog().getTableName(this.p.getTableId(j.t1Alias));
String table2Name = Database.getCatalog().getTableName(this.p.getTableId(j.t2Alias));
String table1Alias = j.t1Alias;
String table2Alias = j.t2Alias;
double t1cost, t2cost;
int t1card, t2card;
boolean leftPkey, rightPkey;
// estimate cost of right subtree
if (doesJoin(plan, table1Alias)) { // j.t1 is in plan already
CostCard c = getCostCard(plan, planCardinalities, planCosts, table1Alias);
t1cost = c.cost; // left side just has cost of whatever left subtree is
t1card = c.card;
leftPkey = hasPkey(plan);
t2cost = j.t2Alias == null ? 0 : stats.get(table2Name).estimateScanCost();
t2card =
j.t2Alias == null
? 0
: stats.get(table2Name).estimateTableCardinality(filterSelectivities.get(j.t2Alias));
rightPkey = j.t2Alias == null ? false : isPkey(j.t2Alias, j.f2PureName);
} else if (doesJoin(plan, j.t2Alias)) { // j.t2 is in plan
// (else if since both j.t1 and j.t2 shouldn't both be)
CostCard c = getCostCard(plan, planCardinalities, planCosts, table2Alias);
t2cost = c.cost;
t2card = c.card;
rightPkey = hasPkey(plan);
t1cost = stats.get(table1Name).estimateScanCost();
t1card = stats.get(table1Name).estimateTableCardinality(filterSelectivities.get(j.t1Alias));
leftPkey = isPkey(j.t1Alias, j.f1PureName);
} else { // Neither is a plan, both are just single tables
t1cost = stats.get(table1Name).estimateScanCost();
t1card = stats.get(table1Name).estimateTableCardinality(filterSelectivities.get(j.t1Alias));
leftPkey = isPkey(j.t1Alias, j.f1PureName);
t2cost = table2Alias == null ? 0 : stats.get(table2Name).estimateScanCost();
t2card =
table2Alias == null
? 0
: stats.get(table2Name).estimateTableCardinality(filterSelectivities.get(j.t2Alias));
rightPkey = table2Alias == null ? false : isPkey(table2Alias, j.f2PureName);
}
double cost1 = estimateJoinCost(j, t1card, t2card, t1cost, t2cost);
LogicalJoinNode j2 = j.swapInnerOuter();
double cost2 = estimateJoinCost(j2, t2card, t1card, t2cost, t1cost);
if (cost2 < cost1) {
boolean tmp;
j = j2;
cost1 = cost2;
tmp = rightPkey;
rightPkey = leftPkey;
leftPkey = tmp;
}
CostCard cc = new CostCard();
cc.card = estimateJoinCardinality(j, t1card, t2card, leftPkey, rightPkey, stats);
cc.cost = cost1;
return cc;
}
