processing/src/main/java/org/apache/druid/segment/join/JoinableFactoryWrapper.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.druid.segment.join;

import com.google.common.base.Preconditions;
import org.apache.druid.java.util.common.IAE;
import org.apache.druid.java.util.common.logger.Logger;
import org.apache.druid.query.Query;
import org.apache.druid.query.cache.CacheKeyBuilder;
import org.apache.druid.query.planning.DataSourceAnalysis;
import org.apache.druid.query.planning.PreJoinableClause;
import org.apache.druid.segment.SegmentReference;
import org.apache.druid.segment.filter.Filters;
import org.apache.druid.segment.join.filter.JoinFilterAnalyzer;
import org.apache.druid.segment.join.filter.JoinFilterPreAnalysis;
import org.apache.druid.segment.join.filter.JoinFilterPreAnalysisKey;
import org.apache.druid.segment.join.filter.JoinableClauses;
import org.apache.druid.segment.join.filter.rewrite.JoinFilterRewriteConfig;
import org.apache.druid.utils.JvmUtils;

import java.util.List;
import java.util.Optional;
import java.util.concurrent.atomic.AtomicLong;
import java.util.function.Function;

/**
 * A wrapper class over {@link JoinableFactory} for working with {@link Joinable} related classes.
 */
public class JoinableFactoryWrapper
{

  private static final byte JOIN_OPERATION = 0x1;
  private static final Logger log = new Logger(JoinableFactoryWrapper.class);

  private final JoinableFactory joinableFactory;

  public JoinableFactoryWrapper(final JoinableFactory joinableFactory)
  {
    this.joinableFactory = Preconditions.checkNotNull(joinableFactory, "joinableFactory");
  }

  /**
   * Creates a Function that maps base segments to {@link HashJoinSegment} if needed (i.e. if the number of join
   * clauses is > 0). If mapping is not needed, this method will return {@link Function#identity()}.
   *
   * @param clauses            Pre-joinable clauses
   * @param cpuTimeAccumulator An accumulator that we will add CPU nanos to; this is part of the function to encourage
   *                           callers to remember to track metrics on CPU time required for creation of Joinables
   * @param query              The query that will be run on the mapped segments. Usually this should be
   *                           {@code analysis.getBaseQuery().orElse(query)}, where "analysis" is a
   *                           {@link DataSourceAnalysis} and "query" is the original
   *                           query from the end user.
   */
  public Function<SegmentReference, SegmentReference> createSegmentMapFn(
      final List<PreJoinableClause> clauses,
      final AtomicLong cpuTimeAccumulator,
      final Query<?> query
  )
  {
    // compute column correlations here and RHS correlated values
    return JvmUtils.safeAccumulateThreadCpuTime(
        cpuTimeAccumulator,
        () -> {
          if (clauses.isEmpty()) {
            return Function.identity();
          } else {
            final JoinableClauses joinableClauses = JoinableClauses.createClauses(clauses, joinableFactory);
            final JoinFilterPreAnalysis joinFilterPreAnalysis = JoinFilterAnalyzer.computeJoinFilterPreAnalysis(
                new JoinFilterPreAnalysisKey(
                    JoinFilterRewriteConfig.forQuery(query),
                    joinableClauses.getJoinableClauses(),
                    query.getVirtualColumns(),
                    Filters.toFilter(query.getFilter())
                )
            );

            return baseSegment ->
                new HashJoinSegment(
                    baseSegment,
                    joinableClauses.getJoinableClauses(),
                    joinFilterPreAnalysis
                );
          }
        }
    );
  }

  /**
   * Compute a cache key prefix for data sources that participate in the RHS of a join. This key prefix
   * can be used in segment level cache or result level cache. The function can return following wrapped in an
   * Optional
   * - Non-empty byte array - If there is join datasource involved and caching is possible. The result includes
   * join condition expression, join type and cache key returned by joinable factory for each {@link PreJoinableClause}
   * - NULL - There is a join but caching is not possible. It may happen if one of the participating datasource
   * in the JOIN is not cacheable.
   *
   * @param dataSourceAnalysis for the join datasource
   * @return the optional cache key to be used as part of query cache key
   * @throws {@link IAE} if this operation is called on a non-join data source
   */
  public Optional<byte[]> computeJoinDataSourceCacheKey(
      final DataSourceAnalysis dataSourceAnalysis
  )
  {
    final List<PreJoinableClause> clauses = dataSourceAnalysis.getPreJoinableClauses();
    if (clauses.isEmpty()) {
      throw new IAE("No join clauses to build the cache key for data source [%s]", dataSourceAnalysis.getDataSource());
    }

    final CacheKeyBuilder keyBuilder;
    keyBuilder = new CacheKeyBuilder(JOIN_OPERATION);
    for (PreJoinableClause clause : clauses) {
      Optional<byte[]> bytes = joinableFactory.computeJoinCacheKey(clause.getDataSource(), clause.getCondition());
      if (!bytes.isPresent()) {
        // Encountered a data source which didn't support cache yet
        log.debug("skipping caching for join since [%s] does not support caching", clause.getDataSource());
        return Optional.empty();
      }
      keyBuilder.appendByteArray(bytes.get());
      keyBuilder.appendString(clause.getCondition().getOriginalExpression());
      keyBuilder.appendString(clause.getPrefix());
      keyBuilder.appendString(clause.getJoinType().name());
    }
    return Optional.of(keyBuilder.build());
  }

}