Index: lucene/CHANGES.txt
===================================================================
--- lucene/CHANGES.txt	(revision 1462883)
+++ lucene/CHANGES.txt	(working copy)
@@ -185,6 +185,9 @@
   IndexDeletionPolicy and InfoStream in order to make an IndexWriterConfig and
   its clone fully independent. (Adrien Grand)
 
+* LUCENE-4893: Facet counts were multiplied as many times as 
+  FacetsCollector.getFacetResults() is called. (Shai Erera)
+
 Documentation
 
 * LUCENE-4841: Added example SimpleSortedSetFacetsExample to show how
Index: lucene/facet/src/java/org/apache/lucene/facet/search/FacetResult.java
===================================================================
--- lucene/facet/src/java/org/apache/lucene/facet/search/FacetResult.java	(revision 1462883)
+++ lucene/facet/src/java/org/apache/lucene/facet/search/FacetResult.java	(working copy)
@@ -1,6 +1,5 @@
 package org.apache.lucene.facet.search;
 
-
 /*
  * Licensed to the Apache Software Foundation (ASF) under one or more
  * contributor license agreements.  See the NOTICE file distributed with
Index: lucene/facet/src/java/org/apache/lucene/facet/search/FacetsAccumulator.java
===================================================================
--- lucene/facet/src/java/org/apache/lucene/facet/search/FacetsAccumulator.java	(revision 1462883)
+++ lucene/facet/src/java/org/apache/lucene/facet/search/FacetsAccumulator.java	(working copy)
@@ -146,6 +146,14 @@
     }
     return clps;
   }
+  
+  private FacetResult emptyResult(int ordinal, FacetRequest fr) {
+    FacetResultNode root = new FacetResultNode();
+    root.ordinal = ordinal;
+    root.label = fr.categoryPath;
+    root.value = 0;
+    return new FacetResult(fr, root, 0);
+  }
 
   /**
    * Used by {@link FacetsCollector} to build the list of {@link FacetResult
@@ -156,6 +164,14 @@
    *          the documents that matched the query, per-segment.
    */
   public List<FacetResult> accumulate(List<MatchingDocs> matchingDocs) throws IOException {
+    if (matchingDocs.isEmpty()) {
+      List<FacetResult> res = new ArrayList<FacetResult>();
+      for (FacetRequest fr : searchParams.facetRequests) {
+        res.add(emptyResult(taxonomyReader.getOrdinal(fr.categoryPath), fr));
+      }
+      return res;
+    }
+    
     // aggregate facets per category list (usually onle one category list)
     FacetsAggregator aggregator = getAggregator();
     for (CategoryListParams clp : getCategoryLists()) {
@@ -173,12 +189,8 @@
     for (FacetRequest fr : searchParams.facetRequests) {
       int rootOrd = taxonomyReader.getOrdinal(fr.categoryPath);
       if (rootOrd == TaxonomyReader.INVALID_ORDINAL) { // category does not exist
-        // Add empty FacetResult:
-        FacetResultNode root = new FacetResultNode();
-        root.ordinal = TaxonomyReader.INVALID_ORDINAL;
-        root.label = fr.categoryPath;
-        root.value = 0;
-        res.add(new FacetResult(fr, root, 0));
+        // Add empty FacetResult
+        res.add(emptyResult(rootOrd, fr));
         continue;
       }
       CategoryListParams clp = searchParams.indexingParams.getCategoryListParams(fr.categoryPath);
Index: lucene/facet/src/java/org/apache/lucene/facet/search/FacetsCollector.java
===================================================================
--- lucene/facet/src/java/org/apache/lucene/facet/search/FacetsCollector.java	(revision 1462883)
+++ lucene/facet/src/java/org/apache/lucene/facet/search/FacetsCollector.java	(working copy)
@@ -204,7 +204,11 @@
    */
   public final List<FacetResult> getFacetResults() throws IOException {
     finish();
-    return accumulator.accumulate(matchingDocs);
+    List<FacetResult> result = accumulator.accumulate(matchingDocs);
+    // clear matchingDocs so that subsequent calls get an empty result, until a
+    // new search is performed.
+    matchingDocs.clear();
+    return result;
   }
   
   /**
Index: lucene/facet/src/test/org/apache/lucene/facet/search/TestFacetsCollector.java
===================================================================
--- lucene/facet/src/test/org/apache/lucene/facet/search/TestFacetsCollector.java	(revision 1462883)
+++ lucene/facet/src/test/org/apache/lucene/facet/search/TestFacetsCollector.java	(working copy)
@@ -230,4 +230,44 @@
     IOUtils.close(taxo, taxoDir, r, indexDir);
   }
 
+  @Test
+  public void testGetFacetResultsTwice() throws Exception {
+    // LUCENE-4893: if getFacetResults was called twice, counts we doubled (and trippled if 3 times...)
+    Directory indexDir = newDirectory();
+    Directory taxoDir = newDirectory();
+    
+    TaxonomyWriter taxonomyWriter = new DirectoryTaxonomyWriter(taxoDir);
+    IndexWriter iw = new IndexWriter(indexDir, newIndexWriterConfig(TEST_VERSION_CURRENT, new MockAnalyzer(random())));
+    
+    FacetFields facetFields = new FacetFields(taxonomyWriter);
+    Document doc = new Document();
+    facetFields.addFields(doc, Arrays.asList(new CategoryPath("a/1", '/'), new CategoryPath("b/1", '/')));
+    iw.addDocument(doc);
+    taxonomyWriter.close();
+    iw.close();
+    
+    DirectoryReader r = DirectoryReader.open(indexDir);
+    DirectoryTaxonomyReader taxo = new DirectoryTaxonomyReader(taxoDir);
+    
+    FacetSearchParams fsp = new FacetSearchParams(
+        new CountFacetRequest(new CategoryPath("a"), 10), 
+        new CountFacetRequest(new CategoryPath("b"), 10));
+    final FacetsAccumulator fa = random().nextBoolean() ? new FacetsAccumulator(fsp, r, taxo) : new StandardFacetsAccumulator(fsp, r, taxo);
+    final FacetsCollector fc = FacetsCollector.create(fa);
+    new IndexSearcher(r).search(new MatchAllDocsQuery(), fc);
+    
+    List<FacetResult> res = fc.getFacetResults();
+    assertEquals(2, res.size());
+    assertEquals(1, (int) res.get(0).getFacetResultNode().subResults.get(0).value);
+    assertEquals(1, (int) res.get(1).getFacetResultNode().subResults.get(0).value);
+
+    // second time should return an empty result for each request
+    res = fc.getFacetResults();
+    assertEquals(2, res.size());
+    assertEquals(0, fc.getFacetResults().get(0).getFacetResultNode().subResults.size());
+    assertEquals(0, fc.getFacetResults().get(1).getFacetResultNode().subResults.size());
+    
+    IOUtils.close(taxo, taxoDir, r, indexDir);
+  }
+  
 }