Package org.apache.druid.segment.index

Class DictionaryScanningBitmapIndex

java.lang.Object
org.apache.druid.segment.index.SimpleBitmapColumnIndex
org.apache.druid.segment.index.SimpleImmutableBitmapIterableIndex
org.apache.druid.segment.index.DictionaryScanningBitmapIndex
All Implemented Interfaces:
BitmapColumnIndex
public abstract class DictionaryScanningBitmapIndex extends SimpleImmutableBitmapIterableIndex
Common BitmapColumnIndex implementation for indexes which are computed by scanning the entire value dictionary of the underlying column to check if the value index matches the filter. Contains logic to skip computing indexes with computeBitmapResult(BitmapResultFactory, int, int, boolean) if 'selectionRowCount' does not equal 'totalRowCount' and 'selectionRowCount' is smaller than dictionarySize multiplied by scaleThreshold. The default scaleThreshold value is 1.0, meaning that if dictionarySize is larger than 'selectionRowCount' we skip using indexes, the idea being we would either have to perform the check against the values in the dictionary or the values in the remaining rows, since remaining rows is smaller we should just do that instead of spending time to compute indexes to further shrink 'selectionRowCount'.

  • Constructor Details

    • DictionaryScanningBitmapIndex

      public DictionaryScanningBitmapIndex(int dictionarySize)

    • DictionaryScanningBitmapIndex

      public DictionaryScanningBitmapIndex(int dictionarySize, double scaleThreshold)

  • Method Details

    • estimatedComputeCost

      public int estimatedComputeCost()
      Description copied from interface: BitmapColumnIndex
      Returns an estimated cost for computing the bitmap result. Generally this is equivalent to number of bitmap union or intersection operations need to be performed. E.x. null value index bitmap has a cost of 0, non-null value index bitmap union with null bitmap has a cost of 1, range (size of 10) scanning index bitmap union with null bitmap has a cost of 10.

    • computeBitmapResult

      @Nullable public final <T> T computeBitmapResult(BitmapResultFactory<T> bitmapResultFactory, int applyRowCount, int totalRowCount, boolean includeUnknown)
      Description copied from interface: BitmapColumnIndex
      Compute a bitmap result wrapped with the BitmapResultFactory representing the rows matched by this index, or null if the index cannot (or should not) be computed.
      Parameters:
      bitmapResultFactory - helper to format the ImmutableBitmap in a form ready for consumption by callers
      applyRowCount - upper bound on number of rows this filter would be applied to, after removing rows short-circuited by prior bundle operations. For example, given "x AND y", if "x" is resolved using an index, then "y" will receive the number of rows that matched the filter "x". As another example, given "x OR y", if "x" is resolved using an index, then "y" will receive the number of rows that did *not* match the filter "x".
      totalRowCount - total number of rows to be scanned if no indexes are used
      includeUnknown - mapping for Druid native two state logic system into SQL three-state logic system. If set to true, bitmaps returned by this method should include true bits for any rows where the matching result is 'unknown', such as from the input being null valued.
      Returns:
      bitmap result representing rows matched by this index