io.trino.sql.planner.iterative.rule.PushLimitThroughUnion Maven / Gradle / Ivy
/*
* 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 io.trino.sql.planner.iterative.rule;
import com.google.common.collect.ImmutableList;
import io.trino.matching.Capture;
import io.trino.matching.Captures;
import io.trino.matching.Pattern;
import io.trino.sql.planner.iterative.Rule;
import io.trino.sql.planner.plan.LimitNode;
import io.trino.sql.planner.plan.PlanNode;
import io.trino.sql.planner.plan.UnionNode;
import static io.trino.matching.Capture.newCapture;
import static io.trino.sql.planner.optimizations.QueryCardinalityUtil.isAtMost;
import static io.trino.sql.planner.plan.Patterns.Limit.requiresPreSortedInputs;
import static io.trino.sql.planner.plan.Patterns.limit;
import static io.trino.sql.planner.plan.Patterns.source;
import static io.trino.sql.planner.plan.Patterns.union;
/**
* Transforms:
*
* - Limit
* - Union
* - relation1
* - relation2
* ..
*
* Into:
*
* - Limit
* - Union
* - Limit
* - relation1
* - Limit
* - relation2
* ..
*
* Applies to LimitNode without ties only to avoid optimizer loop.
*/
public class PushLimitThroughUnion
implements Rule
{
private static final Capture CHILD = newCapture();
private static final Pattern PATTERN = limit()
.matching(limit -> !limit.isWithTies())
.with(requiresPreSortedInputs().equalTo(false))
.with(source().matching(union().capturedAs(CHILD)));
@Override
public Pattern getPattern()
{
return PATTERN;
}
@Override
public Result apply(LimitNode parent, Captures captures, Context context)
{
UnionNode unionNode = captures.get(CHILD);
ImmutableList.Builder builder = ImmutableList.builder();
boolean shouldApply = false;
for (PlanNode source : unionNode.getSources()) {
// This check is to ensure that we don't fire the optimizer if it was previously applied.
if (isAtMost(source, context.getLookup(), parent.getCount())) {
builder.add(source);
}
else {
shouldApply = true;
builder.add(new LimitNode(context.getIdAllocator().getNextId(), source, parent.getCount(), true));
}
}
if (!shouldApply) {
return Result.empty();
}
return Result.ofPlanNode(
parent.replaceChildren(ImmutableList.of(
unionNode.replaceChildren(builder.build()))));
}
}