More defensive configuration of custom page swappers

* We now log when a custom page swapper is being configured.
* If we cannot configure the desired custom page swapper, we now throw an exception to avoid falling back to the default page swapper implementation.

community/kernel/src/main/java/org/neo4j/kernel/impl/pagecache/ConfiguringPageCacheFactory.java

@@ -46,13 +46,13 @@ public class ConfiguringPageCacheFactory
     public ConfiguringPageCacheFactory(
             FileSystemAbstraction fs, Config config, PageCacheTracer tracer, Log log )
     {
-        this.swapperFactory = createAndConfigureSwapperFactory( fs, config );
+        this.swapperFactory = createAndConfigureSwapperFactory( fs, config, log );
         this.config = config;
         this.tracer = tracer;
         this.log = log;
     }
 
-    private PageSwapperFactory createAndConfigureSwapperFactory( FileSystemAbstraction fs, Config config )
+    private PageSwapperFactory createAndConfigureSwapperFactory( FileSystemAbstraction fs, Config config, Log log )
     {
         String desiredImplementation = config.get( pagecache_swapper );
 
@@ -68,9 +68,11 @@ private PageSwapperFactory createAndConfigureSwapperFactory( FileSystemAbstracti
                         ConfigurablePageSwapperFactory configurableFactory = (ConfigurablePageSwapperFactory) factory;
                         configurableFactory.configure( config );
                     }
+                    log.info( "Configured " + pagecache_swapper.name() + ": " + desiredImplementation );
                     return factory;
                 }
             }
+            throw new IllegalArgumentException( "Cannot find PageSwapperFactory: " + desiredImplementation );
         }
 
         SingleFilePageSwapperFactory factory = new SingleFilePageSwapperFactory();

community/kernel/src/test/java/org/neo4j/kernel/impl/pagecache/ConfiguringPageCacheFactoryTest.java

@@ -19,32 +19,34 @@
  */
 package org.neo4j.kernel.impl.pagecache;
 
-import java.util.concurrent.atomic.AtomicBoolean;
-import java.util.concurrent.atomic.AtomicInteger;
-
 import org.junit.Before;
 import org.junit.Rule;
 import org.junit.Test;
 
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicInteger;
+
 import org.neo4j.graphdb.factory.GraphDatabaseSettings;
 import org.neo4j.io.pagecache.PageCache;
 import org.neo4j.io.pagecache.impl.SingleFilePageSwapperFactory;
 import org.neo4j.io.pagecache.tracing.PageCacheTracer;
 import org.neo4j.kernel.configuration.Config;
+import org.neo4j.logging.BufferingLog;
 import org.neo4j.logging.NullLog;
 import org.neo4j.test.EphemeralFileSystemRule;
 
+import static org.hamcrest.CoreMatchers.containsString;
 import static org.hamcrest.CoreMatchers.equalTo;
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.is;
-
 import static org.neo4j.graphdb.factory.GraphDatabaseSettings.mapped_memory_page_size;
 import static org.neo4j.graphdb.factory.GraphDatabaseSettings.pagecache_memory;
 import static org.neo4j.graphdb.factory.GraphDatabaseSettings.pagecache_swapper;
 import static org.neo4j.helpers.collection.MapUtil.stringMap;
 
 public class ConfiguringPageCacheFactoryTest
 {
+    private static final String TEST_IMPL_NAME = "pageswapperForTesting";
     @Rule
     public EphemeralFileSystemRule fsRule = new EphemeralFileSystemRule();
 
@@ -80,19 +82,33 @@ public void shouldUseConfiguredPageSizeAndFitAsManyPagesAsItCan() throws Throwab
     }
 
     @Test
-    public void mustUseConfiguredPageSwapper() throws Exception
+    public void mustUseAndLogConfiguredPageSwapper() throws Exception
     {
         // Given
         Config config = new Config( stringMap(
                 pagecache_memory.name(), "8m",
-                pagecache_swapper.name(), "test" ) );
+                pagecache_swapper.name(), TEST_IMPL_NAME ) );
+        BufferingLog log = new BufferingLog();
 
         // When
-        new ConfiguringPageCacheFactory( fsRule.get(), config, PageCacheTracer.NULL, NullLog.getInstance() );
+        new ConfiguringPageCacheFactory( fsRule.get(), config, PageCacheTracer.NULL, log );
 
         // Then
         assertThat( PageSwapperFactoryForTesting.countCreatedPageSwapperFactories(), is( 1 ) );
         assertThat( PageSwapperFactoryForTesting.countConfiguredPageSwapperFactories(), is( 1 ) );
+        assertThat( log.toString(), containsString( TEST_IMPL_NAME ) );
+    }
+
+    @Test( expected = IllegalArgumentException.class )
+    public void mustThrowIfConfiguredPageSwapperCannotBeFound() throws Exception
+    {
+        // Given
+        Config config = new Config( stringMap(
+                pagecache_memory.name(), "8m",
+                pagecache_swapper.name(), "non-existing" ) );
+
+        // When
+        new ConfiguringPageCacheFactory( fsRule.get(), config, PageCacheTracer.NULL, NullLog.getInstance() );
     }
 
     @Test
@@ -102,7 +118,7 @@ public void mustUsePageSwapperCachePageSizeHintAsDefault() throws Exception
         int cachePageSizeHint = 16 * 1024;
         PageSwapperFactoryForTesting.cachePageSizeHint.set( cachePageSizeHint );
         Config config = new Config( stringMap(
-                GraphDatabaseSettings.pagecache_swapper.name(), "test" ) );
+                GraphDatabaseSettings.pagecache_swapper.name(), TEST_IMPL_NAME ) );
 
         // When
         ConfiguringPageCacheFactory factory = new ConfiguringPageCacheFactory(
@@ -124,7 +140,7 @@ public void mustIgnoreExplicitlySpecifiedCachePageSizeIfPageSwapperHintIsStrict(
         PageSwapperFactoryForTesting.cachePageSizeHintIsStrict.set( true );
         Config config = new Config( stringMap(
                 GraphDatabaseSettings.mapped_memory_page_size.name(), "4096",
-                GraphDatabaseSettings.pagecache_swapper.name(), "test" ) );
+                GraphDatabaseSettings.pagecache_swapper.name(), TEST_IMPL_NAME ) );
 
         // When
         ConfiguringPageCacheFactory factory = new ConfiguringPageCacheFactory(
@@ -164,7 +180,7 @@ public PageSwapperFactoryForTesting()
         @Override
         public String implementationName()
         {
-            return "test";
+            return TEST_IMPL_NAME;
         }
 
         @Override