LIRS cache: improved hit rate

h2/src/docsrc/html/changelog.html

@@ -87,6 +87,9 @@ Change Log
     when using larger databases and many threads.
     To re-enable, use the file name prefix "cache:".
 </li>
+<li>LIRS cache: improved hit rate because now added entries get hot if they 
+    were in the non-resident part of the cache before.
+</li>
 </ul>
 
 <h2>Version 1.4.192 Beta (2016-05-26)</h2>

h2/src/main/org/h2/mvstore/cache/CacheLongKeyLIRS.java

@@ -791,9 +791,12 @@ public class CacheLongKeyLIRS<V> {
             }
             V old;
             Entry<V> e = find(key, hash);
+            boolean existed;
             if (e == null) {
+                existed = false;
                 old = null;
             } else {
+                existed = true;
                 old = e.value;
                 remove(key, hash);
             }
@@ -822,6 +825,10 @@ public class CacheLongKeyLIRS<V> {
             mapSize++;
             // added entries are always added to the stack
             addToStack(e);
+            if (existed) {
+                // if it was there before (even non-resident), it becomes hot
+                access(key, hash);
+            }
             return old;
         }
 

h2/src/test/org/h2/test/store/TestCacheLongKeyLIRS.java

@@ -225,8 +225,9 @@ public class TestCacheLongKeyLIRS extends TestBase {
         test.put(5, 50);
         assertTrue(test.containsValue(50));
         verify(test, "mem: 4 stack: 5 4 3 2 cold: 5 non-resident: 1");
+        // 1 was non-resident, so this should make it hot
         test.put(1, 10);
-        verify(test, "mem: 4 stack: 1 5 4 3 2 cold: 1 non-resident: 5");
+        verify(test, "mem: 4 stack: 1 5 4 3 cold: 2 non-resident: 5");
         assertFalse(test.containsValue(50));
         test.remove(2);
         test.remove(3);