SOLR-14131: Add maxQueryLength option to DirectSolrSpellchecker.

Closes #1113

solr/CHANGES.txt

@@ -170,6 +170,8 @@ Improvements
   SOLR_IP_WHITELIST and SOLR_IP_BLACKLIST. These variables can restrict access to
   Solr based on IP addresses/networks. (rmuir)
 
+* SOLR-14131: Add maxQueryLength option to DirectSolrSpellchecker. (Andy Webb via Bruno Roustant)
+
 Optimizations
 ---------------------
 (No changes)

solr/core/src/java/org/apache/solr/spelling/DirectSolrSpellChecker.java

@@ -54,6 +54,7 @@ import org.slf4j.LoggerFactory;
  *       can be specified as "freq".
  *   <li>thresholdTokenFrequency: sets {@link DirectSpellChecker#setThresholdFrequency(float)}.
  *   <li>minQueryLength: sets {@link DirectSpellChecker#setMinQueryLength(int)}.
+ *   <li>maxQueryLength: sets {@link DirectSpellChecker#setMaxQueryLength(int)}.
  *   <li>maxQueryFrequency: sets {@link DirectSpellChecker#setMaxQueryFrequency(float)}.
  * </ul>
  * @see DirectSpellChecker
@@ -86,6 +87,9 @@ public class DirectSolrSpellChecker extends SolrSpellChecker {
   public static final String MINQUERYLENGTH = "minQueryLength";
   public static final int DEFAULT_MINQUERYLENGTH = 4;
   
+  public static final String MAXQUERYLENGTH = "maxQueryLength";
+  public static final int DEFAULT_MAXQUERYLENGTH = Integer.MAX_VALUE;
+
   public static final String MAXQUERYFREQUENCY = "maxQueryFrequency";
   public static final float DEFAULT_MAXQUERYFREQUENCY = 0.01f;
   
@@ -144,6 +148,11 @@ public class DirectSolrSpellChecker extends SolrSpellChecker {
     Integer queryLength = params.getInt(MINQUERYLENGTH);
     if (queryLength != null)
       minQueryLength = queryLength;
+
+    int maxQueryLength = DEFAULT_MAXQUERYLENGTH;
+    Integer overriddenMaxQueryLength = params.getInt(MAXQUERYLENGTH);
+    if (overriddenMaxQueryLength != null)
+      maxQueryLength = overriddenMaxQueryLength;
     
     float maxQueryFrequency = DEFAULT_MAXQUERYFREQUENCY;
     Float queryFreq = params.getFloat(MAXQUERYFREQUENCY);
@@ -158,6 +167,7 @@ public class DirectSolrSpellChecker extends SolrSpellChecker {
     checker.setThresholdFrequency(minThreshold);
     checker.setMaxInspections(maxInspections);
     checker.setMinQueryLength(minQueryLength);
+    checker.setMaxQueryLength(maxQueryLength);
     checker.setMaxQueryFrequency(maxQueryFrequency);
     checker.setLowerCaseTerms(false);
     

solr/core/src/test/org/apache/solr/spelling/DirectSolrSpellCheckerTest.java

@@ -62,20 +62,25 @@ public class DirectSolrSpellCheckerTest extends SolrTestCaseJ4 {
     checker.init(spellchecker, core);
 
     h.getCore().withSearcher(searcher -> {
+
+      // check that 'fob' is corrected to 'foo'
       Collection<Token> tokens = queryConverter.convert("fob");
       SpellingOptions spellOpts = new SpellingOptions(tokens, searcher.getIndexReader());
       SpellingResult result = checker.getSuggestions(spellOpts);
-      assertTrue("result is null and it shouldn't be", result != null);
+      assertNotNull("result shouldn't be null", result);
       Map<String, Integer> suggestions = result.get(tokens.iterator().next());
+      assertFalse("suggestions shouldn't be empty", suggestions.isEmpty());
       Map.Entry<String, Integer> entry = suggestions.entrySet().iterator().next();
-      assertTrue(entry.getKey() + " is not equal to " + "foo", entry.getKey().equals("foo") == true);
+      assertEquals("foo", entry.getKey());
       assertFalse(entry.getValue() + " equals: " + SpellingResult.NO_FREQUENCY_INFO, entry.getValue() == SpellingResult.NO_FREQUENCY_INFO);
 
+      // check that 'super' is *not* corrected
       spellOpts.tokens = queryConverter.convert("super");
       result = checker.getSuggestions(spellOpts);
-      assertTrue("result is null and it shouldn't be", result != null);
+      assertNotNull("result shouldn't be null", result);
-      suggestions = result.get(tokens.iterator().next());
+      suggestions = result.get(spellOpts.tokens.iterator().next());
-      assertTrue("suggestions is not null and it should be", suggestions == null);
+      assertNotNull("suggestions shouldn't be null", suggestions);
+      assertTrue("suggestions should be empty", suggestions.isEmpty());
       return null;
     });
   }
@@ -88,6 +93,46 @@ public class DirectSolrSpellCheckerTest extends SolrTestCaseJ4 {
         "//lst[@name='spellcheck']/lst[@name='suggestions']/lst[@name='fox']/arr[@name='suggestion']/lst/int[@name='freq']=2",
         "//lst[@name='spellcheck']/bool[@name='correctlySpelled']='true'"
     );
-  }  
+  }
+
+  @Test
+  public void testMaxQueryLength() throws Exception {
+    testMaxQueryLength(true);
+    testMaxQueryLength(false);
+  }
+
+  private void testMaxQueryLength(Boolean limitQueryLength) throws Exception {
+
+    DirectSolrSpellChecker checker = new DirectSolrSpellChecker();
+    NamedList<Object> spellchecker = new NamedList<>();
+    spellchecker.add("classname", DirectSolrSpellChecker.class.getName());
+    spellchecker.add(SolrSpellChecker.FIELD, "teststop");
+    spellchecker.add(DirectSolrSpellChecker.MINQUERYLENGTH, 2);
+
+    // demonstrate that "anothar" is not corrected when maxQueryLength is set to a small number
+    if (limitQueryLength) spellchecker.add(DirectSolrSpellChecker.MAXQUERYLENGTH, 4);
+
+    SolrCore core = h.getCore();
+    checker.init(spellchecker, core);
+
+    h.getCore().withSearcher(searcher -> {
+      Collection<Token> tokens = queryConverter.convert("anothar");
+      SpellingOptions spellOpts = new SpellingOptions(tokens, searcher.getIndexReader());
+      SpellingResult result = checker.getSuggestions(spellOpts);
+      assertNotNull("result shouldn't be null", result);
+      Map<String, Integer> suggestions = result.get(tokens.iterator().next());
+      assertNotNull("suggestions shouldn't be null", suggestions);
+
+      if (limitQueryLength) {
+        assertTrue("suggestions should be empty", suggestions.isEmpty());
+      } else {
+        assertFalse("suggestions shouldn't be empty", suggestions.isEmpty());
+        Map.Entry<String, Integer> entry = suggestions.entrySet().iterator().next();
+        assertEquals("another", entry.getKey());
+      }
+
+      return null;
+    });
+  }
   
 }

solr/solr-ref-guide/src/spell-checking.adoc

@@ -69,6 +69,7 @@ The `DirectSolrSpellChecker` uses terms from the Solr index without building a p
     <int name="minPrefix">1</int>
     <int name="maxInspections">5</int>
     <int name="minQueryLength">4</int>
+    <int name="maxQueryLength">40</int>
     <float name="maxQueryFrequency">0.01</float>
     <float name="thresholdTokenFrequency">.01</float>
   </lst>
@@ -81,7 +82,7 @@ Many of the parameters relate to how this spell checker should query the index f
 
 Because this spell checker is querying the main index, you may want to limit how often it queries the index to be sure to avoid any performance conflicts with user queries. The `accuracy` setting defines the threshold for a valid suggestion, while `maxEdits` defines the number of changes to the term to allow. Since most spelling mistakes are only 1 letter off, setting this to 1 will reduce the number of possible suggestions (the default, however, is 2); the value can only be 1 or 2. `minPrefix` defines the minimum number of characters the terms should share. Setting this to 1 means that the spelling suggestions will all start with the same letter, for example.
 
-The `maxInspections` parameter defines the maximum number of possible matches to review before returning results; the default is 5. `minQueryLength` defines how many characters must be in the query before suggestions are provided; the default is 4.
+The `maxInspections` parameter defines the maximum number of possible matches to review before returning results; the default is 5. `minQueryLength` defines how many characters must be in the query before suggestions are provided; the default is 4. `maxQueryLength` enables the spell checker to skip over very long query terms, which can avoid expensive operations or exceptions. There is no limit to term length by default.
 
 At first, spellchecker analyses incoming query words by looking up them in the index. Only query words, which are absent in index or too rare ones (below `maxQueryFrequency`) are considered as misspelled and used for finding suggestions. Words which are frequent than `maxQueryFrequency` bypass spellchecker unchanged. After suggestions for every misspelled word are found they are filtered for enough frequency with `thresholdTokenFrequency` as boundary value. These parameters (`maxQueryFrequency` and `thresholdTokenFrequency`) can be a percentage (such as .01, or 1%) or an absolute value (such as 4).