Class FieldComparator<T>

Direct Known Subclasses:
DocComparator, FieldComparator.RelevanceComparator, FieldComparator.TermOrdValComparator, FieldComparator.TermValComparator, NumericComparator, SimpleFieldComparator

public abstract class FieldComparator<T> extends Object
Expert: a FieldComparator compares hits so as to determine their sort order when collecting the top results with TopFieldCollector. The concrete public FieldComparator classes here correspond to the SortField types.

The document IDs passed to these methods must only move forwards, since they are using doc values iterators to retrieve sort values.

This API is designed to achieve high performance sorting, by exposing a tight interaction with FieldValueHitQueue as it visits hits. Whenever a hit is competitive, it's enrolled into a virtual slot, which is an int ranging from 0 to numHits-1. Segment transitions are handled by creating a dedicated per-segment LeafFieldComparator which also needs to interact with the FieldValueHitQueue but can optimize based on the segment to collect.

The following functions need to be implemented

See Also:
WARNING: This API is experimental and might change in incompatible ways in the next release.
  • Constructor Details

    • FieldComparator

      public FieldComparator()
  • Method Details

    • compare

      public abstract int compare(int slot1, int slot2)
      Compare hit at slot1 with hit at slot2.
      slot1 - first slot to compare
      slot2 - second slot to compare
      any N < 0 if slot2's value is sorted after slot1, any N > 0 if the slot2's value is sorted before slot1 and 0 if they are equal
    • setTopValue

      public abstract void setTopValue(T value)
      Record the top value, for future calls to LeafFieldComparator.compareTop(int). This is only called for searches that use searchAfter (deep paging), and is called before any calls to getLeafComparator(LeafReaderContext).
    • value

      public abstract T value(int slot)
      Return the actual value in the slot.
      slot - the value
      value in this slot
    • getLeafComparator

      public abstract LeafFieldComparator getLeafComparator(LeafReaderContext context) throws IOException
      Get a per-segment LeafFieldComparator to collect the given LeafReaderContext. All docIDs supplied to this LeafFieldComparator are relative to the current reader (you must add docBase if you need to map it to a top-level docID).
      context - current reader context
      the comparator to use for this segment
      IOException - if there is a low-level IO error
    • compareValues

      public int compareValues(T first, T second)
      Returns a negative integer if first is less than second, 0 if they are equal and a positive integer otherwise. Default impl to assume the type implements Comparable and invoke .compareTo; be sure to override this method if your FieldComparator's type isn't a Comparable or if your values may sometimes be null
    • setSingleSort

      public void setSingleSort()
      Informs the comparator that sort is done on this single field. This is useful to enable some optimizations for skipping non-competitive documents.
    • disableSkipping

      public void disableSkipping()
      Informs the comparator that the skipping of documents should be disabled. This function is called by TopFieldCollector in cases when the skipping functionality should not be applied or not necessary. An example could be when search sort is a part of the index sort, and can be already efficiently handled by TopFieldCollector, and doing extra work for skipping in the comparator is redundant.