contrib/storage-mongo/src/main/java/org/apache/drill/exec/store/mongo/MongoPushDownFilterForScan.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.apache.drill.exec.store.mongo;

import java.io.IOException;

import org.apache.drill.common.exceptions.DrillRuntimeException;
import org.apache.drill.common.expression.LogicalExpression;
import org.apache.drill.exec.planner.logical.DrillOptiq;
import org.apache.drill.exec.planner.logical.DrillParseContext;
import org.apache.drill.exec.planner.logical.RelOptHelper;
import org.apache.drill.exec.planner.physical.FilterPrel;
import org.apache.drill.exec.planner.physical.PrelUtil;
import org.apache.drill.exec.planner.physical.ScanPrel;
import org.apache.drill.exec.store.StoragePluginOptimizerRule;
import org.apache.calcite.rel.RelNode;
import org.apache.calcite.plan.RelOptRuleCall;
import org.apache.calcite.rex.RexNode;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import org.apache.drill.shaded.guava.com.google.common.collect.ImmutableList;

public class MongoPushDownFilterForScan extends StoragePluginOptimizerRule {
  private static final Logger logger = LoggerFactory
      .getLogger(MongoPushDownFilterForScan.class);
  public static final StoragePluginOptimizerRule INSTANCE = new MongoPushDownFilterForScan();

  private MongoPushDownFilterForScan() {
    super(
        RelOptHelper.some(FilterPrel.class, RelOptHelper.any(ScanPrel.class)),
        "MongoPushDownFilterForScan");
  }

  @Override
  public void onMatch(RelOptRuleCall call) {
    final ScanPrel scan = (ScanPrel) call.rel(1);
    final FilterPrel filter = (FilterPrel) call.rel(0);
    final RexNode condition = filter.getCondition();

    MongoGroupScan groupScan = (MongoGroupScan) scan.getGroupScan();
    if (groupScan.isFilterPushedDown()) {
      return;
    }

    LogicalExpression conditionExp = DrillOptiq.toDrill(
        new DrillParseContext(PrelUtil.getPlannerSettings(call.getPlanner())), scan, condition);
    MongoFilterBuilder mongoFilterBuilder = new MongoFilterBuilder(groupScan,
        conditionExp);
    MongoScanSpec newScanSpec = mongoFilterBuilder.parseTree();
    if (newScanSpec == null) {
      return; // no filter pushdown so nothing to apply.
    }

    MongoGroupScan newGroupsScan = null;
    try {
      newGroupsScan = new MongoGroupScan(groupScan.getUserName(), groupScan.getStoragePlugin(),
          newScanSpec, groupScan.getColumns());
    } catch (IOException e) {
      logger.error(e.getMessage(), e);
      throw new DrillRuntimeException(e.getMessage(), e);
    }
    newGroupsScan.setFilterPushedDown(true);

    final ScanPrel newScanPrel = new ScanPrel(scan.getCluster(), filter.getTraitSet(),
        newGroupsScan, scan.getRowType(), scan.getTable());

    if (mongoFilterBuilder.isAllExpressionsConverted()) {
      /*
       * Since we could convert the entire filter condition expression into an
       * Mongo filter, we can eliminate the filter operator altogether.
       */
      call.transformTo(newScanPrel);
    } else {
      call.transformTo(filter.copy(filter.getTraitSet(),
          ImmutableList.of((RelNode) newScanPrel)));
    }

  }

  @Override
  public boolean matches(RelOptRuleCall call) {
    final ScanPrel scan = (ScanPrel) call.rel(1);
    if (scan.getGroupScan() instanceof MongoGroupScan) {
      return super.matches(call);
    }
    return false;
  }

}