processing/src/main/java/org/apache/druid/segment/StorageAdapter.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;

import org.apache.druid.guice.annotations.PublicApi;
import org.apache.druid.segment.column.ColumnCapabilities;
import org.apache.druid.segment.data.Indexed;
import org.joda.time.DateTime;
import org.joda.time.Interval;

import javax.annotation.Nullable;

/**
 */
@PublicApi
public interface StorageAdapter extends CursorFactory, ColumnInspector
{
  Interval getInterval();
  Indexed<String> getAvailableDimensions();
  Iterable<String> getAvailableMetrics();

  /**
   * Returns the number of distinct values for the given column if known, or {@link Integer#MAX_VALUE} if unknown,
   * e. g. the column is numeric. If the column doesn't exist, returns 0.
   */
  int getDimensionCardinality(String column);
  DateTime getMinTime();
  DateTime getMaxTime();
  @Nullable
  Comparable getMinValue(String column);
  @Nullable
  Comparable getMaxValue(String column);

  /**
   * Returns capabilities of a particular column, if known. May be null if the column doesn't exist, or if
   * the column does exist but the capabilities are unknown. The latter is possible with dynamically discovered
   * columns.
   *
   * Note that StorageAdapters are representations of "real" segments, so they are not aware of any virtual columns
   * that may be involved in a query. In general, query engines should instead use the method
   * {@link ColumnSelectorFactory#getColumnCapabilities(String)}, which returns capabilities for virtual columns as
   * well.
   *
   * @param column column name
   *
   * @return capabilities, or null
   */
  @Override
  @Nullable
  ColumnCapabilities getColumnCapabilities(String column);

  /**
   * Like {@link ColumnCapabilities#getType()}, but may return a more descriptive string for complex columns.
   * @param column column name
   * @return type name
   */
  @Nullable
  String getColumnTypeName(String column);
  int getNumRows();
  DateTime getMaxIngestedEventTime();
  Metadata getMetadata();

  /**
   * Returns true if this storage adapter can filter some rows out. The actual column cardinality can be lower than
   * what {@link #getDimensionCardinality} returns if this returns true. Dimension selectors for such storage adapter
   * can return non-contiguous dictionary IDs because the dictionary IDs in filtered rows will not be returned.
   * Note that the number of rows accessible via this storage adapter will not necessarily decrease because of
   * the built-in filters. For inner joins, for example, the number of joined rows can be larger than
   * the number of rows in the base adapter even though this method returns true.
   */
  default boolean hasBuiltInFilters()
  {
    return false;
  }
}