org.apache.druid.frame.segment.FrameCursorUtils Maven / Gradle / Ivy

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A module that is everything required to understands Druid Segments
There is a newer version: 30.0.1
/*
 * 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.frame.segment;

import org.apache.druid.error.DruidException;
import org.apache.druid.frame.Frame;
import org.apache.druid.frame.write.FrameWriter;
import org.apache.druid.frame.write.FrameWriterFactory;
import org.apache.druid.java.util.common.Intervals;
import org.apache.druid.java.util.common.guava.Sequence;
import org.apache.druid.java.util.common.guava.Sequences;
import org.apache.druid.query.filter.BoundDimFilter;
import org.apache.druid.query.filter.Filter;
import org.apache.druid.query.ordering.StringComparators;
import org.apache.druid.segment.Cursor;
import org.apache.druid.segment.column.ColumnHolder;
import org.apache.druid.segment.filter.BoundFilter;
import org.apache.druid.segment.filter.Filters;
import org.joda.time.Interval;

import javax.annotation.Nullable;
import java.util.Arrays;
import java.util.Iterator;
import java.util.NoSuchElementException;

public class FrameCursorUtils
{
  private FrameCursorUtils()
  {
    // No instantiation.
  }

  /**
   * Builds a {@link Filter} from a {@link Filter} plus an {@link Interval}. Useful when we want to do a time filter
   * on a frame, but can't push the time filter into the frame itself (perhaps because it isn't time-sorted).
   */
  @Nullable
  public static Filter buildFilter(@Nullable Filter filter, Interval interval)
  {
    if (Intervals.ETERNITY.equals(interval)) {
      return filter;
    } else {
      return Filters.and(
          Arrays.asList(
              new BoundFilter(
                  new BoundDimFilter(
                      ColumnHolder.TIME_COLUMN_NAME,
                      String.valueOf(interval.getStartMillis()),
                      String.valueOf(interval.getEndMillis()),
                      false,
                      true,
                      null,
                      null,
                      StringComparators.NUMERIC
                  )
              ),
              filter
          )
      );
    }
  }

  /**
   * Writes a {@link Cursor} to a sequence of {@link Frame}. This method iterates over the rows of the cursor,
   * and writes the columns to the frames
   *
   * @param cursor                 Cursor to write to the frame
   * @param frameWriterFactory     Frame writer factory to write to the frame.
   *                               Determines the signature of the rows that are written to the frames
   */
  public static Sequence cursorToFrames(
      Cursor cursor,
      FrameWriterFactory frameWriterFactory
  )
  {

    return Sequences.simple(
        () -> new Iterator()
        {
          @Override
          public boolean hasNext()
          {
            return !cursor.isDone();
          }

          @Override
          public Frame next()
          {
            // Makes sure that cursor contains some elements prior. This ensures if no row is written, then the row size
            // is larger than the MemoryAllocators returned by the provided factory
            if (!hasNext()) {
              throw new NoSuchElementException();
            }
            boolean firstRowWritten = false;
            Frame frame;
            try (final FrameWriter frameWriter = frameWriterFactory.newFrameWriter(cursor.getColumnSelectorFactory())) {
              while (!cursor.isDone()) {
                if (!frameWriter.addSelection()) {
                  break;
                }
                firstRowWritten = true;
                cursor.advance();
              }

              if (!firstRowWritten) {
                throw DruidException
                    .forPersona(DruidException.Persona.DEVELOPER)
                    .ofCategory(DruidException.Category.CAPACITY_EXCEEDED)
                    .build("Subquery's row size exceeds the frame size and therefore cannot write the subquery's "
                           + "row to the frame. This is a non-configurable static limit that can only be modified by the "
                           + "developer.");
              }

              frame = Frame.wrap(frameWriter.toByteArray());
            }
            return frame;
          }
        }
    );
  }
}