Allow configuration of lucene query term limit

fixes #2834

protected/humhub/docs/CHANGELOG.md

@@ -4,6 +4,7 @@ HumHub Change Log
 -------------------------
 - Fix: Added `ManageSpaces` and SystemAdmin check to `UserGroupAccessValidator`.
 - Fix: Only include content with `stream_channel = default` into spacechooser update count.
+- Enh: Make lucene search term limit configurable via `ZendLuceneSearch::$searchItemLimit`.
 
 1.2.3  (October 23, 2017)
 -------------------------

protected/humhub/docs/guide/admin/search.md

@@ -43,4 +43,32 @@ You can modify the default search directory in the [configuration](advanced-conf
         ]
         // ...
     ];
-```
+```
+
+### Limitations
+
+The Zend Lucence Engine runs inside the PHP process and is limited by the
+settings of the PHP environment in terms of memory usage and execution time.
+
+By default Zend Lucence Engine sets a limit on the number of terms in a search query,
+which also results in a limitation of the number of items a search term can match.
+
+For the space search this must be set at least as high as the number of spaces.
+In general the limit depends on the number of items a search term can match so it
+highly depends on the content. To be sure all searches work you can set it higher than the
+number of spaces/users/content you have.
+
+It can be set to 0 for no limitation, but that may result in search queries
+to fail caused by high memory usage.
+
+You can [configure](advanced-configuration.md) the limit by setting `searchItemLimit` on the `search` application component:
+
+```php
+return [
+    'components' => [
+        'search' => [
+            'searchItemLimit' => 10000,
+        ],
+    ],
+];
+```

protected/humhub/modules/search/engine/ZendLuceneSearch.php

@@ -15,6 +15,7 @@ use humhub\modules\search\libs\SearchResultSet;
 use humhub\modules\space\models\Space;
 use ZendSearch\Lucene\Document\Field;
 use yii\helpers\VarDumper;
+use ZendSearch\Lucene\Lucene;
 
 /**
  * ZendLucenceSearch Engine
@@ -30,6 +31,24 @@ class ZendLuceneSearch extends Search
      */
     public $index = null;
 
+    /**
+     * @var integer sets the `termsPerQueryLimit` property for the lucene index.
+     * This limits the number of terms in a search query, which also results in a
+     * limitation of the number of items a search term can match.
+     *
+     * This property should be at least as high as the number of items a search can match.
+     * It needs to be configured dependent on the amount of items stored in the
+     * Humhub database.
+     *
+     * It can be set to 0 for no limitation, but that may result in search queries
+     * to fail caused by high memory usage.
+     *
+     * Defaults to 2048, which is twice as high as the default value set by Lucene.
+     *
+     * @see Lucene::getTermsPerQueryLimit()
+     */
+    public $searchItemLimit = 2048;
+
     /**
      * @inheritdoc
      */
@@ -285,6 +304,8 @@ class ZendLuceneSearch extends Search
         \ZendSearch\Lucene\Analysis\Analyzer\Analyzer::setDefault(new \ZendSearch\Lucene\Analysis\Analyzer\Common\Utf8Num\CaseInsensitive());
         \ZendSearch\Lucene\Search\QueryParser::setDefaultOperator(\ZendSearch\Lucene\Search\QueryParser::B_AND);
 
+        \ZendSearch\Lucene\Lucene::setTermsPerQueryLimit($this->searchItemLimit);
+
         try {
             $index = \ZendSearch\Lucene\Lucene::open($this->getIndexPath());
         } catch (\ZendSearch\Lucene\Exception\RuntimeException $ex) {