[LUCENE-5015] Unexpected performance difference between SamplingAccumulator and StandardFacetAccumulator

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 4.3
• Fix Version/s: 4.4, 6.0
• Component/s: modules/facet
• Lucene Fields: New, Patch Available
• Assignee: Shai Erera
• Reporter: Rob Audenaerde
• Created: 23/May/13 08:02
• Updated: 28/Aug/22 13:46
• Resolved: 29/May/13 08:29

Description

I have an unexpected performance difference between the SamplingAccumulator and the StandardFacetAccumulator.

The case is an index with about 5M documents and each document containing about 10 fields. I created a facet on each of those fields. When searching to retrieve facet-counts (using 1 CountFacetRequest), the SamplingAccumulator is about twice as fast as the StandardFacetAccumulator. This is expected and a nice speed-up.

However, when I use more CountFacetRequests to retrieve facet-counts for more than one field, the speeds of the SampingAccumulator decreases, to the point where the StandardFacetAccumulator is faster.

 
FacetRequests  Sampling    Standard
 1               391 ms     1100 ms
 2               531 ms     1095 ms 
 3               948 ms     1108 ms
 4              1400 ms     1110 ms
 5              1901 ms     1102 ms

Is this behaviour normal? I did not expect it, as the SamplingAccumulator needs to do less work?

Some code to show what I do:

	searcher.search( facetsQuery, facetsCollector );
	final List<FacetResult> collectedFacets = facetsCollector.getFacetResults();

final FacetSearchParams facetSearchParams = new FacetSearchParams( facetRequests );

FacetsCollector facetsCollector;

if ( isSampled )
{
	facetsCollector =
		FacetsCollector.create( new SamplingAccumulator( new RandomSampler(), facetSearchParams, searcher.getIndexReader(), taxo ) );
}
else
{
	facetsCollector = FacetsCollector.create( FacetsAccumulator.create( facetSearchParams, searcher.getIndexReader(), taxo ) );