content: /*
   * 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.cassandra.index.sai.disk.v1.segment;
  
  import java.util.Iterator;
  import java.util.Map;
  import java.util.concurrent.atomic.LongAdder;
  import javax.annotation.concurrent.NotThreadSafe;
  
  import org.apache.cassandra.config.DatabaseDescriptor;
  import org.apache.cassandra.db.tries.InMemoryTrie;
  import org.apache.cassandra.index.sai.postings.PostingList;
  import org.apache.cassandra.index.sai.utils.IndexEntry;
  import org.apache.cassandra.utils.Throwables;
  import org.apache.cassandra.utils.bytecomparable.ByteComparable;
  import org.apache.lucene.util.packed.PackedInts;
  import org.apache.lucene.util.packed.PackedLongValues;
  
  /**
   * On-heap buffer for values that provides a sorted view of itself as an {@link Iterator}.
   */
  @NotThreadSafe
  public class SegmentTrieBuffer
  {
      private static final int MAX_RECURSIVE_TERM_LENGTH = 128;
  
      private final InMemoryTrie<PackedLongValues.Builder> trie;
      private final PostingsAccumulator postingsAccumulator;
      private int numRows;
  
      public SegmentTrieBuffer()
      {
          trie = new InMemoryTrie<>(DatabaseDescriptor.getMemtableAllocationType().toBufferType());
          postingsAccumulator = new PostingsAccumulator();
      }
  
      public int numRows()
      {
          return numRows;
      }
  
      public long memoryUsed()
      {
          return trie.sizeOnHeap() + postingsAccumulator.heapAllocations();
      }
  
      public long add(ByteComparable term, int termLength, int segmentRowId)
      {
          final long initialSizeOnHeap = trie.sizeOnHeap();
          final long reducerHeapSize = postingsAccumulator.heapAllocations();
  
          try
          {
              trie.putSingleton(term, segmentRowId, postingsAccumulator, termLength <= MAX_RECURSIVE_TERM_LENGTH);
          }
          catch (InMemoryTrie.SpaceExhaustedException e)
          {
              throw Throwables.unchecked(e);
          }
  
          numRows++;
          return (trie.sizeOnHeap() - initialSizeOnHeap) + (postingsAccumulator.heapAllocations() - reducerHeapSize);
      }
  
      public Iterator<IndexEntry> iterator()
      {
          Iterator<Map.Entry<ByteComparable, PackedLongValues.Builder>> iterator = trie.entrySet().iterator();
  
          return new Iterator<>()
          {
              @Override
              public boolean hasNext()
              {
                  return iterator.hasNext();
              }
  
              @Override
              public IndexEntry next()
              {
                  Map.Entry<ByteComparable, PackedLongValues.Builder> entry = iterator.next();
                  PackedLongValues postings = entry.getValue().build();
                  PackedLongValues.Iterator postingsIterator = postings.iterator();
                  return IndexEntry.create(entry.getKey(), new PostingList()
                  {
                      @Override
                      public long nextPosting()
                      {
                          if (postingsIterator.hasNext())
                              return postingsIterator.next();
                          return END_OF_STREAM;
                      }
  
                      @Override
                      public long size()
                      {
                          return postings.size();
                      }
  
                      @Override
                      public long advance(long targetRowID)
                      {
                          throw new UnsupportedOperationException();
                      }
                  });
              }
          };
      }
  
      private static class PostingsAccumulator implements InMemoryTrie.UpsertTransformer<PackedLongValues.Builder, Integer>
      {
          private final LongAdder heapAllocations = new LongAdder();
  
          @Override
          public PackedLongValues.Builder apply(PackedLongValues.Builder existing, Integer rowID)
          {
              if (existing == null)
              {
                  existing = PackedLongValues.deltaPackedBuilder(PackedInts.COMPACT);
                  heapAllocations.add(existing.ramBytesUsed());
              }
              long ramBefore = existing.ramBytesUsed();
              existing.add(rowID);
              heapAllocations.add(existing.ramBytesUsed() - ramBefore);
              return existing;
          }
  
          long heapAllocations()
          {
              return heapAllocations.longValue();
          }
      }
  }
  