def _create_tree_topology(self, pattern: Pattern, statistics: Dict,
leaves: List[TreePlanNode]):
if StatisticsTypes.ARRIVAL_RATES in statistics and \
StatisticsTypes.SELECTIVITY_MATRIX in statistics and \
len(statistics) == 2:
selectivity_matrix = statistics[StatisticsTypes.SELECTIVITY_MATRIX]
arrival_rates = statistics[StatisticsTypes.ARRIVAL_RATES]
else:
raise MissingStatisticsException()
order = self._get_initial_order(selectivity_matrix, arrival_rates)
args_num = len(order)
items = tuple(order)
suborders = {(i, ): (TreePlanLeafNode(i),
self._get_plan_cost(pattern, TreePlanLeafNode(i),
statistics))
for i in items}
tree_to_second_min_tree_map = {}
invariants = ZStreamTreeInvariants(self._get_plan_cost)
all_sub_trees = []
# iterate over suborders sizes
for i in range(2, args_num + 1):
# iterate over suborders of size i
for j in range(args_num - i + 1):
# create the suborder (slice) to find its optimum.
suborder = tuple(order[t] for t in range(j, j + i))
# use first split of suborder as speculative best.
order1_, order2_ = suborder[:1], suborder[1:]
tree1_, _ = suborders[order1_]
tree2_, _ = suborders[order2_]
tree = TreePlanBuilder._instantiate_binary_node(
pattern, tree1_, tree2_)
cost = self._get_plan_cost(pattern, tree, statistics)
suborders[suborder] = tree, cost
second_prev_cost = cost
second_min_tree = tree
# iterate over splits of suborder
for k in range(2, i):
# find the optimal topology of this split, according to optimal topologies of subsplits.
order1, order2 = suborder[:k], suborder[k:]
tree1, _ = suborders[order1]
tree2, _ = suborders[order2]
_, prev_cost = suborders[suborder]
new_tree = TreePlanBuilder._instantiate_binary_node(
pattern, tree1, tree2)
new_cost = self._get_plan_cost(pattern, new_tree,
statistics)
if new_cost < prev_cost:
second_prev_cost = prev_cost
second_min_tree = suborders[suborder][0]
suborders[suborder] = new_tree, new_cost
elif new_cost < second_prev_cost or second_min_tree == tree:
second_prev_cost = new_cost
second_min_tree = new_tree
if i != 2:
tree_to_second_min_tree_map[suborders[suborder]
[0]] = second_min_tree
# Eliminates all trees that are not in best tree from map_tree_to_second_min_tree
InvariantAwareZStreamTreeBuilder.__get_relevant_sub_trees(
suborders[items][0], all_sub_trees)
for tree in all_sub_trees:
invariants.add(Invariant(tree, tree_to_second_min_tree_map[tree]))
# return the topology (index 0 at tuple) of the entire order, indexed to 'items'
return suborders[items][0], invariants