Update lookup od neostore data source in data source manager to

use last available database as a default database;
update extension lookup to use NeoStoreDataSource directly.

community/kernel/src/main/java/org/neo4j/kernel/NeoStoreDataSource.java

@@ -349,6 +349,7 @@ public void start() throws IOException
         dataSourceDependencies.satisfyDependency( monitors );
         dataSourceDependencies.satisfyDependency( tokenHolders );
         dataSourceDependencies.satisfyDependency( facade );
+        dataSourceDependencies.satisfyDependency( this );
 
         life = new LifeSupport();
         dataSourceDependencies.satisfyDependency( explicitIndexProvider );

community/kernel/src/main/java/org/neo4j/kernel/impl/transaction/state/DataSourceManager.java

@@ -24,6 +24,7 @@
 import java.util.function.Supplier;
 
 import org.neo4j.helpers.Listeners;
+import org.neo4j.helpers.collection.Iterables;
 import org.neo4j.internal.kernel.api.Kernel;
 import org.neo4j.kernel.NeoStoreDataSource;
 import org.neo4j.kernel.lifecycle.LifeSupport;
@@ -83,7 +84,7 @@ public void unregister( NeoStoreDataSource dataSource )
 
     public NeoStoreDataSource getDataSource()
     {
-        return dataSources.get( 0 );
+        return Iterables.last( dataSources );
     }
 
     @Override
@@ -126,6 +127,6 @@ public void shutdown()
     @Override
     public Kernel get()
     {
-        return dataSources.get( 0 ).getKernel();
+        return getDataSource().getKernel();
     }
 }

enterprise/kernel/src/main/java/org/neo4j/kernel/impl/pagecache/PageCacheWarmerKernelExtension.java

@@ -26,8 +26,8 @@
 import org.neo4j.io.fs.FileSystemAbstraction;
 import org.neo4j.io.pagecache.PageCache;
 import org.neo4j.kernel.AvailabilityGuard;
+import org.neo4j.kernel.NeoStoreDataSource;
 import org.neo4j.kernel.configuration.Config;
-import org.neo4j.kernel.impl.transaction.state.DataSourceManager;
 import org.neo4j.kernel.impl.transaction.state.NeoStoreFileListing;
 import org.neo4j.kernel.lifecycle.LifecycleAdapter;
 import org.neo4j.logging.Log;
@@ -36,18 +36,18 @@
 class PageCacheWarmerKernelExtension extends LifecycleAdapter
 {
     private final AvailabilityGuard availabilityGuard;
-    private final DataSourceManager dataSourceManager;
+    private final NeoStoreDataSource dataSource;
     private final Config config;
     private final PageCacheWarmer pageCacheWarmer;
     private final WarmupAvailabilityListener availabilityListener;
     private volatile boolean started;
 
     PageCacheWarmerKernelExtension(
             JobScheduler scheduler, AvailabilityGuard availabilityGuard, PageCache pageCache, FileSystemAbstraction fs,
-            DataSourceManager dataSourceManager, Log log, PageCacheWarmerMonitor monitor, Config config )
+            NeoStoreDataSource dataSource, Log log, PageCacheWarmerMonitor monitor, Config config )
     {
         this.availabilityGuard = availabilityGuard;
-        this.dataSourceManager = dataSourceManager;
+        this.dataSource = dataSource;
         this.config = config;
         pageCacheWarmer = new PageCacheWarmer( fs, pageCache, scheduler );
         availabilityListener = new WarmupAvailabilityListener( scheduler, pageCacheWarmer, config, log, monitor );
@@ -79,6 +79,6 @@ public void stop() throws Throwable
 
     private NeoStoreFileListing getNeoStoreFileListing()
     {
-        return dataSourceManager.getDataSource().getDependencyResolver().resolveDependency( NeoStoreFileListing.class );
+        return dataSource.getDependencyResolver().resolveDependency( NeoStoreFileListing.class );
     }
 }

enterprise/kernel/src/main/java/org/neo4j/kernel/impl/pagecache/PageCacheWarmerKernelExtensionFactory.java

@@ -26,12 +26,12 @@
 import org.neo4j.io.fs.FileSystemAbstraction;
 import org.neo4j.io.pagecache.PageCache;
 import org.neo4j.kernel.AvailabilityGuard;
+import org.neo4j.kernel.NeoStoreDataSource;
 import org.neo4j.kernel.configuration.Config;
 import org.neo4j.kernel.extension.ExtensionType;
 import org.neo4j.kernel.extension.KernelExtensionFactory;
 import org.neo4j.kernel.impl.logging.LogService;
 import org.neo4j.kernel.impl.spi.KernelContext;
-import org.neo4j.kernel.impl.transaction.state.DataSourceManager;
 import org.neo4j.kernel.lifecycle.Lifecycle;
 import org.neo4j.kernel.monitoring.Monitors;
 import org.neo4j.logging.Log;
@@ -51,7 +51,7 @@ public interface Dependencies
 
         FileSystemAbstraction fileSystemAbstraction();
 
-        DataSourceManager getDataSourceManager();
+        NeoStoreDataSource getDataSource();
 
         LogService logService();
 
@@ -73,7 +73,7 @@ public Lifecycle newInstance( KernelContext context, Dependencies deps )
         PageCache pageCache = deps.pageCache();
         FileSystemAbstraction fs = deps.fileSystemAbstraction();
         LogService logService = deps.logService();
-        DataSourceManager dataSourceManager = deps.getDataSourceManager();
+        NeoStoreDataSource dataSourceManager = deps.getDataSource();
         Log log = logService.getInternalLog( PageCacheWarmer.class );
         PageCacheWarmerMonitor monitor = deps.monitors().newMonitor( PageCacheWarmerMonitor.class );
         Config config = deps.config();