Remap id's returned in XXXFilteredDimensionSpec.getRow() as per reduced cardinality

[himanshug]

fixes the issue described in # #2255

[cheddar]

👍

[binlijin]

Some place use the dimension cardinality before the dimension decorate, if this has no problem i think this can be accepted.

public class TopNQueryEngine
{
  public Sequence<Result<TopNResultValue>> query(final TopNQuery query, final StorageAdapter adapter)
  {
   ...
    final Function<Cursor, Result<TopNResultValue>> mapFn = getMapFn(query, adapter);

    return Sequences.filter(
        Sequences.map(
            adapter.makeCursors(filter, queryIntervals.get(0), granularity),
            new Function<Cursor, Result<TopNResultValue>>()
            {
              @Override
              public Result<TopNResultValue> apply(Cursor input)
              {
                log.debug("Running over cursor[%s]", adapter.getInterval(), input.getTime());
                return mapFn.apply(input);
              }
            }
        ),
        Predicates.<Result<TopNResultValue>>notNull()
    );
  }

  private Function<Cursor, Result<TopNResultValue>> getMapFn(TopNQuery query, final StorageAdapter adapter)
  {
    final Capabilities capabilities = adapter.getCapabilities();
    final String dimension = query.getDimensionSpec().getDimension();

   //before dimension decorate
    final int cardinality = adapter.getDimensionCardinality(dimension); 
    ...
    final TopNAlgorithmSelector selector = new TopNAlgorithmSelector(cardinality, numBytesPerRecord);

    final TopNAlgorithm topNAlgorithm;
    ...
    return new TopNMapFn(query, topNAlgorithm);
  }
}

public class TopNMapFn implements Function<Cursor, Result<TopNResultValue>>
{
  public Result<TopNResultValue> apply(Cursor cursor)
  {
    // dimension decorate
    final DimensionSelector dimSelector = cursor.makeDimensionSelector(
        query.getDimensionSpec()
    );    }
}

[himanshug]

@binlijin that cardinality is only used to choose an algorithm, buffer I'm talking about is at https://github.com/druid-io/druid/blob/master/processing/src/main/java/io/druid/query/topn/PooledTopNAlgorithm.java#L67

[binlijin]

@himanshug thanks, i am just want to make sure there is no problem, because i am not familiar with all logic.

[guobingkun]

line55 could be:

this.isWhitelist = isWhitelist == null || isWhitelist.booleanValue();

[guobingkun]

👍