/*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.facebook.presto.sql.planner.iterative.rule;
import com.facebook.presto.Session;
import com.facebook.presto.sql.planner.DependencyExtractor;
import com.facebook.presto.sql.planner.ExpressionSymbolInliner;
import com.facebook.presto.sql.planner.PlanNodeIdAllocator;
import com.facebook.presto.sql.planner.Symbol;
import com.facebook.presto.sql.planner.SymbolAllocator;
import com.facebook.presto.sql.planner.iterative.Lookup;
import com.facebook.presto.sql.planner.iterative.Rule;
import com.facebook.presto.sql.planner.plan.Assignments;
import com.facebook.presto.sql.planner.plan.PlanNode;
import com.facebook.presto.sql.planner.plan.ProjectNode;
import com.facebook.presto.sql.tree.Expression;
import com.facebook.presto.sql.tree.Literal;
import com.facebook.presto.sql.tree.TryExpression;
import com.facebook.presto.sql.util.AstUtils;
import com.google.common.collect.Sets;
import java.util.Map;
import java.util.Optional;
import java.util.Set;
import java.util.function.Function;
import java.util.stream.Collectors;
import static java.util.stream.Collectors.toSet;
/**
* Inlines expressions from a child project node into a parent project node
* as long as they are simple constants, or they are referenced only once (to
* avoid introducing duplicate computation) and the references don't appear
* within a TRY block (to avoid changing semantics).
*/
public class InlineProjections
implements Rule
{
@Override
public Optional<PlanNode> apply(PlanNode node, Lookup lookup, PlanNodeIdAllocator idAllocator, SymbolAllocator symbolAllocator, Session session)
{
if (!(node instanceof ProjectNode)) {
return Optional.empty();
}
ProjectNode parent = (ProjectNode) node;
PlanNode source = lookup.resolve(parent.getSource());
if (!(source instanceof ProjectNode)) {
return Optional.empty();
}
ProjectNode child = (ProjectNode) source;
Sets.SetView<Symbol> targets = extractInliningTargets(parent, child);
if (targets.isEmpty()) {
return Optional.empty();
}
// inline the expressions
Assignments assignments = child.getAssignments().filter(targets::contains);
Map<Symbol, Expression> parentAssignments = parent.getAssignments()
.entrySet().stream()
.collect(Collectors.toMap(
Map.Entry::getKey,
entry -> inlineReferences(entry.getValue(), assignments)));
// Synthesize identity assignments for the inputs of expressions that were inlined
// to place in the child projection.
// If all assignments end up becoming identity assignments, they'll get pruned by
// other rules
Set<Symbol> inputs = child.getAssignments()
.entrySet().stream()
.filter(entry -> targets.contains(entry.getKey()))
.map(Map.Entry::getValue)
.flatMap(entry -> DependencyExtractor.extractAll(entry).stream())
.collect(toSet());
Assignments.Builder childAssignments = Assignments.builder();
for (Map.Entry<Symbol, Expression> assignment : child.getAssignments().entrySet()) {
if (!targets.contains(assignment.getKey())) {
childAssignments.put(assignment);
}
}
for (Symbol input : inputs) {
childAssignments.putIdentity(input);
}
return Optional.of(
new ProjectNode(
parent.getId(),
new ProjectNode(
child.getId(),
child.getSource(),
childAssignments.build()),
Assignments.copyOf(parentAssignments)));
}
private Expression inlineReferences(Expression expression, Assignments assignments)
{
Function<Symbol, Expression> mapping = symbol -> {
Expression result = assignments.get(symbol);
if (result != null) {
return result;
}
return symbol.toSymbolReference();
};
return new ExpressionSymbolInliner(mapping).rewrite(expression);
}
private Sets.SetView<Symbol> extractInliningTargets(ProjectNode parent, ProjectNode child)
{
// candidates for inlining are
// 1. references to simple constants
// 2. references to complex expressions that
// a. are not inputs to try() expressions
// b. appear only once across all expressions
// c. are not identity projections
Map<Symbol, Long> dependencies = parent.getAssignments()
.getExpressions().stream()
.flatMap(expression -> DependencyExtractor.extractAll(expression).stream())
.collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));
// find references to simple constants
Set<Symbol> constants = dependencies.keySet().stream()
.filter(input -> child.getAssignments().get(input) instanceof Literal)
.collect(toSet());
// exclude any complex inputs to TRY expressions. Inlining them would potentially
// change the semantics of those expressions
Set<Symbol> tryArguments = parent.getAssignments()
.getExpressions().stream()
.flatMap(expression -> extractTryArguments(expression).stream())
.collect(toSet());
Set<Symbol> singletons = dependencies.entrySet().stream()
.filter(entry -> entry.getValue() == 1) // reference appears just once across all expressions in parent project node
.filter(entry -> !tryArguments.contains(entry.getKey())) // they are not inputs to TRY. Otherwise, inlining might change semantics
.filter(entry -> !child.getAssignments().isIdentity(entry.getKey())) // skip identities, otherwise, this rule will keep firing forever
.map(Map.Entry::getKey)
.collect(toSet());
return Sets.union(singletons, constants);
}
private Set<Symbol> extractTryArguments(Expression expression)
{
return AstUtils.preOrder(expression)
.filter(TryExpression.class::isInstance)
.map(TryExpression.class::cast)
.flatMap(tryExpression -> DependencyExtractor.extractAll(tryExpression).stream())
.collect(toSet());
}
}