Speed up phrase suggestion scoring

Two changes:
1.  In the StupidBackoffScorer only look for the trigram if there is a bigram.
2.  Cache the frequencies in WordScorer so we don't look them up again and
again and again.  This is implemented by wrapping the TermsEnum in a special
purpose wrapper that really only works in context of the WordScorer.

This provides a pretty substantial speedup when there are many candidates.

Closes #5395

src/main/java/org/elasticsearch/search/suggest/phrase/StupidBackoffScorer.java

@@ -54,18 +54,18 @@ public class StupidBackoffScorer extends WordScorer {
 
     @Override
     protected double scoreTrigram(Candidate w, Candidate w_1, Candidate w_2) throws IOException {
-        SuggestUtils.join(separator, spare, w_2.term, w_1.term, w.term);
+        // First see if there are bigrams.  If there aren't then skip looking up the trigram.  This saves lookups
-        final long trigramCount = frequency(spare);
+        // when the bigrams and trigrams are rare and we need both anyway.
-        if (trigramCount < 1) {
-            SuggestUtils.join(separator, spare, w_1.term, w.term);
-            final long count = frequency(spare);
-            if (count < 1) {
-                return discount * scoreUnigram(w);
-            }
-            return discount * (count / (w_1.frequency + 0.00000000001d));
-        }
         SuggestUtils.join(separator, spare, w_1.term, w.term);
-        final long bigramCount = frequency(spare);
+        long bigramCount = frequency(spare);
+        if (bigramCount < 1) {
+            return discount * scoreUnigram(w);
+        }
+        SuggestUtils.join(separator, spare, w_2.term, w_1.term, w.term);
+        long trigramCount = frequency(spare);
+        if (trigramCount < 1) {
+            return discount * (bigramCount / (w_1.frequency + 0.00000000001d));
+        }
         return trigramCount / (bigramCount + 0.00000000001d);
     }
 

src/main/java/org/elasticsearch/search/suggest/phrase/WordScorer.java

@@ -18,10 +18,11 @@
  */
 package org.elasticsearch.search.suggest.phrase;
 
-import org.apache.lucene.index.IndexReader;
+import com.carrotsearch.hppc.ObjectObjectMap;
-import org.apache.lucene.index.MultiFields;
+import com.carrotsearch.hppc.ObjectObjectOpenHashMap;
-import org.apache.lucene.index.Terms;
+import org.apache.lucene.index.*;
-import org.apache.lucene.index.TermsEnum;
+import org.apache.lucene.index.FilterAtomicReader.FilterTermsEnum;
+import org.apache.lucene.util.Bits;
 import org.apache.lucene.util.BytesRef;
 import org.elasticsearch.ElasticsearchIllegalArgumentException;
 import org.elasticsearch.search.suggest.phrase.DirectCandidateGenerator.Candidate;
@@ -35,7 +36,7 @@ public abstract class WordScorer {
     protected final String field;
     protected final Terms terms;
     protected final long vocabluarySize;
-    protected double realWordLikelyhood;
+    protected final double realWordLikelyhood;
     protected final BytesRef spare = new BytesRef();
     protected final BytesRef separator;
     protected final TermsEnum termsEnum;
@@ -56,17 +57,17 @@ public abstract class WordScorer {
         this.vocabluarySize =  vocSize == -1 ? reader.maxDoc() : vocSize;
         this.useTotalTermFreq = vocSize != -1;
         this.numTerms = terms.size();
-        this.termsEnum = terms.iterator(null);
+        this.termsEnum = new FrequencyCachingTermsEnumWrapper(terms.iterator(null));
         this.reader = reader;
         this.realWordLikelyhood = realWordLikelyHood;
         this.separator = separator;
-   }
+    }
 
-   public long frequency(BytesRef term) throws IOException {
+    public long frequency(BytesRef term) throws IOException {
-      if (termsEnum.seekExact(term)) {
+        if (termsEnum.seekExact(term)) {
-          return useTotalTermFreq ? termsEnum.totalTermFreq() : termsEnum.docFreq();
+            return useTotalTermFreq ? termsEnum.totalTermFreq() : termsEnum.docFreq();
-      }
+        }
-      return 0;
+        return 0;
    }
 
    protected double channelScore(Candidate candidate, Candidate original) throws IOException {
@@ -94,7 +95,7 @@ public abstract class WordScorer {
        return scoreUnigram(word);
    }
    
-   protected double scoreTrigram(Candidate word, Candidate w_1, Candidate w_2)  throws IOException {
+   protected double scoreTrigram(Candidate word, Candidate w_1, Candidate w_2) throws IOException {
        return scoreBigram(word, w_1);
    }
 
@@ -102,4 +103,85 @@ public abstract class WordScorer {
        public WordScorer newScorer(IndexReader reader, Terms terms,
             String field, double realWordLikelyhood, BytesRef separator) throws IOException;
    }
+
+   /**
+    * Terms enum wrapper that caches term frequencies in an effort to outright skip seeks.  Only works with seekExact(BytesRef), not next or
+    * not seekCeil.  Because of this it really only makes sense in this context.
+    */
+   private static class FrequencyCachingTermsEnumWrapper extends FilterTermsEnum {
+       private ObjectObjectMap<BytesRef, CacheEntry> cache = new ObjectObjectOpenHashMap<BytesRef, CacheEntry>();
+       /**
+        * The last term that the called attempted to seek to.
+        */
+       private CacheEntry last;
+
+       public FrequencyCachingTermsEnumWrapper(TermsEnum in) {
+           super(in);
+       }
+
+       @Override
+       public boolean seekExact(BytesRef text) throws IOException {
+           last = cache.get(text);
+           if (last != null) {
+               // This'll fail to work properly if the user seeks but doesn't check the frequency, causing us to cache it.
+               // That is OK because WordScorer only seeks to check the frequency.
+               return last.ttf != 0 || last.df != 0;
+           }
+           last = new CacheEntry();
+           cache.put(BytesRef.deepCopyOf(text), last);
+           if (in.seekExact(text)) {
+               // Found so mark the term uncached.
+               last.df = -1;
+               last.ttf = -1;
+               return true;
+           }
+           // Not found.  The cache will default to 0 for the freqs, meaning not found.
+           return false;
+       }
+
+       @Override
+       public long totalTermFreq() throws IOException {
+           if (last.ttf == -1) {
+               last.ttf = in.totalTermFreq();
+           }
+           return last.ttf;
+       }
+
+       @Override
+       public int docFreq() throws IOException {
+           if (last.df == -1) {
+               last.df = in.docFreq();
+           }
+           return last.df;
+       }
+
+       @Override
+       public void seekExact(long ord) throws IOException {
+           throw new UnsupportedOperationException();
+       }
+
+       @Override
+       public DocsEnum docs(Bits liveDocs, DocsEnum reuse, int flags) throws IOException {
+           throw new UnsupportedOperationException();
+       }
+
+       @Override
+       public DocsAndPositionsEnum docsAndPositions(Bits liveDocs, DocsAndPositionsEnum reuse, int flags) throws IOException {
+           throw new UnsupportedOperationException();
+       }
+
+       public SeekStatus seekCeil(BytesRef text) throws IOException {
+           throw new UnsupportedOperationException();
+       }
+
+       @Override
+       public BytesRef next() {
+           throw new UnsupportedOperationException();
+       }
+
+       private static class CacheEntry {
+           private long ttf;
+           private int df;
+       }
+   }
 }

src/test/java/org/elasticsearch/search/suggest/SuggestSearchTests.java

@@ -20,11 +20,13 @@
 package org.elasticsearch.search.suggest;
 
 import com.google.common.base.Charsets;
+import com.google.common.collect.ImmutableList;
 import com.google.common.io.Resources;
 import org.apache.lucene.util.LuceneTestCase.Slow;
 import org.elasticsearch.ElasticsearchException;
 import org.elasticsearch.ElasticsearchIllegalStateException;
 import org.elasticsearch.action.admin.indices.create.CreateIndexRequestBuilder;
+import org.elasticsearch.action.index.IndexRequestBuilder;
 import org.elasticsearch.action.search.*;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.common.xcontent.XContentFactory;
@@ -931,6 +933,156 @@ public class SuggestSearchTests extends ElasticsearchIntegrationTest {
         assertSuggestion(searchSuggest, 0, 0, "simple_phrase", "nobel prize");
     }
 
+    /**
+     * If the suggester finds tons of options then picking the right one is slow without <<<INSERT SOLUTION HERE>>>.
+     */
+    @Test
+    public void suggestWithManyCandidates() throws InterruptedException, ExecutionException, IOException {
+        CreateIndexRequestBuilder builder = prepareCreate("test").setSettings(settingsBuilder()
+                .put(indexSettings())
+                .put(SETTING_NUMBER_OF_SHARDS, 1) // A single shard will help to keep the tests repeatable.
+                .put(SETTING_NUMBER_OF_REPLICAS, between(0, cluster().size() - 1))
+                .put("index.analysis.analyzer.text.tokenizer", "standard")
+                .putArray("index.analysis.analyzer.text.filter", "lowercase", "my_shingle")
+                .put("index.analysis.filter.my_shingle.type", "shingle")
+                .put("index.analysis.filter.my_shingle.output_unigrams", true)
+                .put("index.analysis.filter.my_shingle.min_shingle_size", 2)
+                .put("index.analysis.filter.my_shingle.max_shingle_size", 3));
+
+        XContentBuilder mapping = XContentFactory.jsonBuilder()
+                .startObject()
+                    .startObject("type1")
+                        .startObject("properties")
+                            .startObject("title")
+                                .field("type", "string")
+                                .field("analyzer", "text")
+                            .endObject()
+                        .endObject()
+                    .endObject()
+                .endObject();
+        assertAcked(builder.addMapping("type1", mapping));
+        ensureGreen();
+
+        ImmutableList.Builder<String> titles = ImmutableList.<String>builder();
+
+        // We're going to be searching for:
+        //   united states house of representatives elections in washington 2006
+        // But we need to make sure we generate a ton of suggestions so we add a bunch of candidates.
+        // Many of these candidates are drawn from page names on English Wikipedia.
+
+        // Tons of different options very near the exact query term
+        titles.add("United States House of Representatives Elections in Washington 1789");
+        for (int year = 1790; year < 2014; year+= 2) {
+            titles.add("United States House of Representatives Elections in Washington " + year);
+        }
+        // Six of these are near enough to be viable suggestions, just not the top one
+
+        // But we can't stop there!  Titles that are just a year are pretty common so lets just add one per year
+        // since 0.  Why not?
+        for (int year = 0; year < 2015; year++) {
+            titles.add(Integer.toString(year));
+        }
+        // That ought to provide more less good candidates for the last term
+
+        // Now remove or add plural copies of every term we can
+        titles.add("State");
+        titles.add("Houses of Parliament");
+        titles.add("Representative Government");
+        titles.add("Election");
+
+        // Now some possessive
+        titles.add("Washington's Birthday");
+
+        // And some conjugation
+        titles.add("Unified Modeling Language");
+        titles.add("Unite Against Fascism");
+        titles.add("Stated Income Tax");
+        titles.add("Media organizations housed within colleges");
+
+        // And other stuff
+        titles.add("Untied shoelaces");
+        titles.add("Unit circle");
+        titles.add("Untitled");
+        titles.add("Unicef");
+        titles.add("Unrated");
+        titles.add("UniRed");
+        titles.add("Jalan Uniten–Dengkil"); // Highway in Malaysia
+        titles.add("UNITAS");
+        titles.add("UNITER");
+        titles.add("Un-Led-Ed");
+        titles.add("STATS LLC");
+        titles.add("Staples");
+        titles.add("Skates");
+        titles.add("Statues of the Liberators");
+        titles.add("Staten Island");
+        titles.add("Statens Museum for Kunst");
+        titles.add("Hause"); // The last name or the German word, whichever.
+        titles.add("Hose");
+        titles.add("Hoses");
+        titles.add("Howse Peak");
+        titles.add("The Hoose-Gow");
+        titles.add("Hooser");
+        titles.add("Electron");
+        titles.add("Electors");
+        titles.add("Evictions");
+        titles.add("Coronal mass ejection");
+        titles.add("Wasington"); // A film?
+        titles.add("Warrington"); // A town in England
+        titles.add("Waddington"); // Lots of places have this name
+        titles.add("Watlington"); // Ditto
+        titles.add("Waplington"); // Yup, also a town
+        titles.add("Washing of the Spears"); // Book
+
+        for (char c = 'A'; c <= 'Z'; c++) {
+            // Can't forget lists, glorious lists!
+            titles.add("List of former members of the United States House of Representatives (" + c + ")");
+
+            // Lots of people are named Washington <Middle Initial>. LastName
+            titles.add("Washington " + c + ". Lastname");
+
+            // Lets just add some more to be evil
+            titles.add("United " + c);
+            titles.add("States " + c);
+            titles.add("House " + c);
+            titles.add("Elections " + c);
+            titles.add("2006 " + c);
+            titles.add(c + " United");
+            titles.add(c + " States");
+            titles.add(c + " House");
+            titles.add(c + " Elections");
+            titles.add(c + " 2006");
+        }
+
+        List<IndexRequestBuilder> builders = new ArrayList<IndexRequestBuilder>();
+        for (String title: titles.build()) {
+            builders.add(client().prepareIndex("test", "type1").setSource("title", title));
+        }
+        indexRandom(true, builders);
+
+        PhraseSuggestionBuilder suggest = phraseSuggestion("title")
+                .field("title")
+                .addCandidateGenerator(PhraseSuggestionBuilder.candidateGenerator("title")
+                        .suggestMode("always")
+                        .maxTermFreq(.99f)
+                        .size(1000) // Setting a silly high size helps of generate a larger list of candidates for testing.
+                        .maxInspections(1000) // This too
+                )
+                .confidence(0f)
+                .maxErrors(2f)
+                .shardSize(30000)
+                .size(30000);
+        Suggest searchSuggest = searchSuggest("united states house of representatives elections in washington 2006", suggest);
+        assertSuggestion(searchSuggest, 0, 0, "title", "united states house of representatives elections in washington 2006");
+        assertSuggestionSize(searchSuggest, 0, 25480, "title");  // Just to prove that we've run through a ton of options
+
+        suggest.size(1);
+        long start = System.currentTimeMillis();
+        searchSuggest = searchSuggest("united states house of representatives elections in washington 2006", suggest);
+        long total = System.currentTimeMillis() - start;
+        assertSuggestion(searchSuggest, 0, 0, "title", "united states house of representatives elections in washington 2006");
+        assertThat(total, lessThan(1000L)); // Takes many seconds without fix
+    }
+    
     protected Suggest searchSuggest(SuggestionBuilder<?>... suggestion) {
         return searchSuggest(null, suggestion);
     }