LUCENE-6918: LRUQueryCache.onDocIdSetEviction is only called when at least one DocIdSet is being evicted. (Adrien Grand)

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1717947 13f79535-47bb-0310-9956-ffa450edef68

lucene/CHANGES.txt

@@ -119,6 +119,11 @@ Optimizations
   particular to rewrite queries that look like: "+*:* #filter" to a
   "ConstantScore(filter)". (Adrien Grand)
 
+Bug Fixes
+
+* LUCENE-6918: LRUQueryCache.onDocIdSetEviction is only called when at least
+  one DocIdSet is being evicted. (Adrien Grand)
+
 ======================= Lucene 5.4.0 =======================
 
 New Features

lucene/core/src/java/org/apache/lucene/search/LRUQueryCache.java

@@ -297,7 +297,13 @@ public class LRUQueryCache implements QueryCache, Accountable {
     final LeafCache leafCache = cache.remove(coreKey);
     if (leafCache != null) {
       ramBytesUsed -= HASHTABLE_RAM_BYTES_PER_ENTRY;
-      onDocIdSetEviction(coreKey, leafCache.cache.size(), leafCache.ramBytesUsed);
+      final int numEntries = leafCache.cache.size();
+      if (numEntries > 0) {
+        onDocIdSetEviction(coreKey, numEntries, leafCache.ramBytesUsed);
+      } else {
+        assert numEntries == 0;
+        assert leafCache.ramBytesUsed == 0;
+      }
     }
   }
 

lucene/core/src/test/org/apache/lucene/search/TestLRUQueryCache.java

@@ -1165,4 +1165,31 @@ public class TestLRUQueryCache extends LuceneTestCase {
     searcher.getIndexReader().close();
     dir.close();
   }
+
+  public void testEvictEmptySegmentCache() throws IOException {
+    Directory dir = newDirectory();
+    final RandomIndexWriter w = new RandomIndexWriter(random(), dir);
+    w.addDocument(new Document());
+    final DirectoryReader reader = w.getReader();
+    final IndexSearcher searcher = newSearcher(reader);
+    final LRUQueryCache queryCache = new LRUQueryCache(2, 100000) {
+      @Override
+      protected void onDocIdSetEviction(Object readerCoreKey, int numEntries, long sumRamBytesUsed) {
+        super.onDocIdSetEviction(readerCoreKey, numEntries, sumRamBytesUsed);
+        assertTrue(numEntries > 0);
+      }
+    };
+
+    searcher.setQueryCache(queryCache);
+    searcher.setQueryCachingPolicy(QueryCachingPolicy.ALWAYS_CACHE);
+
+    Query query = new DummyQuery();
+    searcher.count(query);
+    assertEquals(Collections.singletonList(query), queryCache.cachedQueries());
+    queryCache.clearQuery(query);
+
+    reader.close(); // make sure this does not trigger eviction of segment caches with no entries
+    w.close();
+    dir.close();
+  }
 }