@Override public List<List<LeafNodePlan>> split(List<LeafNodePlan> initialPlans) { // We determine the maximum number of possible merge joins! final HashMap<Item, LinkedList<LeafNodePlan>> mergeJoins = new HashMap<Item, LinkedList<LeafNodePlan>>(); for (final LeafNodePlan tp : initialPlans) { for (final Variable var : tp.getVariables()) { // just the group the leaf nodes with common variables together (this group can be surely // joined only with merge joins) LinkedList<LeafNodePlan> lltp = mergeJoins.get(var); if (lltp == null) { lltp = new LinkedList<LeafNodePlan>(); } lltp.add(tp); mergeJoins.put(var, lltp); } } // determine the group the most possible merge joins int maxMergeJoins = 0; for (final LinkedList<LeafNodePlan> lltp : mergeJoins.values()) { if (lltp.size() > maxMergeJoins) { maxMergeJoins = lltp.size(); } } // avoid the trivial cases (only few merge joins or the whole leaf nodes form a star-shaped // join) if (maxMergeJoins > 2 && maxMergeJoins < initialPlans.size()) { final LinkedList<LeafNodePlan> otherSubgraph = new LinkedList<LeafNodePlan>(); for (final LinkedList<LeafNodePlan> lltp : mergeJoins.values()) { if (lltp.size() == maxMergeJoins) { // determine the other leaf nodes, which are not contained in the subgraph with maximum // number of merge joins! for (LeafNodePlan lfp : initialPlans) { if (!lltp.contains(lfp)) { otherSubgraph.add(lfp); } } // now check if otherSubGraph contains a cartesian product, which would be unacceptable! List<List<LeafNodePlan>> cartesianProduct2 = SplitCartesianProduct.cartesianProducts(otherSubgraph); if (cartesianProduct2.size() <= 1) { // no cartesian product detected => acceptable splitting! List<List<LeafNodePlan>> result = new LinkedList<List<LeafNodePlan>>(); result.add(lltp); result.add(otherSubgraph); return result; } } } } // this strategy did not work! List<List<LeafNodePlan>> result = new LinkedList<List<LeafNodePlan>>(); result.add(initialPlans); return result; }
@Override protected BasicIndexScan getIndex( final LeafNodePlan plan, final BasicIndexScan indexScan, final Collection<Variable> sortCriterium, final Map<Variable, Literal> minima, final Map<Variable, Literal> maxima) { BasicIndexScan index1 = new MemoryIndexScan( (OperatorIDTuple) null, plan.getTriplePatterns(), indexScan.getGraphConstraint(), indexScan.getRoot()); index1.setIntersectionVariables(plan.getVariables()); index1.setUnionVariables(plan.getVariables()); return index1; }