Disable id reuse by default, allow turn it on by idReuse feature flag

in EnterpriseCoreEditionModule.

enterprise/causal-clustering/src/main/java/org/neo4j/causalclustering/core/EnterpriseCoreEditionModule.java

@@ -99,13 +99,16 @@
 import org.neo4j.logging.LogProvider;
 import org.neo4j.ssl.SslPolicy;
 import org.neo4j.udc.UsageData;
+import org.neo4j.unsafe.impl.internal.dragons.FeatureToggles;
 
 /**
  * This implementation of {@link org.neo4j.kernel.impl.factory.EditionModule} creates the implementations of services
  * that are specific to the Enterprise Core edition that provides a core cluster.
  */
 public class EnterpriseCoreEditionModule extends EditionModule
 {
+    static boolean idReuse = FeatureToggles.flag( EnterpriseCoreEditionModule.class, "idReuse", false );
+
     private final ConsensusModule consensusModule;
     private final CoreTopologyService topologyService;
     private final LogProvider logProvider;
@@ -224,11 +227,12 @@ public void registerEditionSpecificProcedures( Procedures procedures ) throws Ke
         coreStateMachinesModule = new CoreStateMachinesModule( identityModule.myself(), platformModule, clusterStateDirectory.get(),
                 config, replicationModule.getReplicator(), consensusModule.raftMachine(), dependencies, localDatabase );
 
+        this.idTypeConfigurationProvider = coreStateMachinesModule.idTypeConfigurationProvider;
+
         createIdComponents( platformModule, dependencies, coreStateMachinesModule.idGeneratorFactory );
         dependencies.satisfyDependency( idGeneratorFactory );
         dependencies.satisfyDependency( idController );
 
-        this.idTypeConfigurationProvider = coreStateMachinesModule.idTypeConfigurationProvider;
         this.labelTokenHolder = coreStateMachinesModule.labelTokenHolder;
         this.propertyKeyTokenHolder = coreStateMachinesModule.propertyKeyTokenHolder;
         this.relationshipTypeTokenHolder = coreStateMachinesModule.relationshipTypeTokenHolder;
@@ -252,9 +256,17 @@ public void registerEditionSpecificProcedures( Procedures procedures ) throws Ke
     protected void createIdComponents( PlatformModule platformModule, Dependencies dependencies,
             IdGeneratorFactory editionIdGeneratorFactory )
     {
-        super.createIdComponents( platformModule, dependencies, editionIdGeneratorFactory );
-        this.idGeneratorFactory =
-                new FreeIdFilteredIdGeneratorFactory( this.idGeneratorFactory, coreStateMachinesModule.freeIdCondition );
+        if ( idReuse )
+        {
+            super.createIdComponents( platformModule, dependencies, editionIdGeneratorFactory );
+            this.idGeneratorFactory = new FreeIdFilteredIdGeneratorFactory( this.idGeneratorFactory,
+                    coreStateMachinesModule.freeIdCondition );
+        }
+        else
+        {
+            idController = createDefaultIdController();
+            this.idGeneratorFactory = new FreeIdFilteredIdGeneratorFactory( editionIdGeneratorFactory, () -> false );
+        }
     }
 
     static Predicate<String> fileWatcherFileNameFilter()

enterprise/causal-clustering/src/test/java/org/neo4j/causalclustering/scenarios/ClusterIdReuseIT.java → enterprise/causal-clustering/src/test/java/org/neo4j/causalclustering/core/ClusterIdReuseIT.java

@@ -17,10 +17,11 @@
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
-package org.neo4j.causalclustering.scenarios;
+package org.neo4j.causalclustering.core;
 
 
 import org.apache.commons.lang3.mutable.MutableLong;
+import org.junit.After;
 import org.junit.Before;
 import org.junit.Rule;
 import org.junit.Test;
@@ -51,9 +52,16 @@ public class ClusterIdReuseIT
     @Before
     public void setUp() throws Exception
     {
+        EnterpriseCoreEditionModule.idReuse = true;
         cluster = clusterRule.startCluster();
     }
 
+    @After
+    public void tearDown()
+    {
+        EnterpriseCoreEditionModule.idReuse = false;
+    }
+
     @Test
     public void shouldReuseIdsInCluster() throws Exception
     {

enterprise/causal-clustering/src/test/java/org/neo4j/causalclustering/core/EnterpriseCoreEditionModuleIntegrationTest.java

@@ -19,6 +19,7 @@
  */
 package org.neo4j.causalclustering.core;
 
+import org.junit.After;
 import org.junit.Rule;
 import org.junit.Test;
 
@@ -31,15 +32,19 @@
 import org.neo4j.graphdb.DependencyResolver;
 import org.neo4j.kernel.impl.index.IndexConfigStore;
 import org.neo4j.kernel.impl.storageengine.impl.recordstorage.id.BufferedIdController;
+import org.neo4j.kernel.impl.storageengine.impl.recordstorage.id.DefaultIdController;
 import org.neo4j.kernel.impl.storageengine.impl.recordstorage.id.IdController;
 import org.neo4j.kernel.impl.store.MetaDataStore;
+import org.neo4j.kernel.impl.store.id.IdGenerator;
 import org.neo4j.kernel.impl.store.id.IdGeneratorFactory;
+import org.neo4j.kernel.impl.store.id.IdType;
 import org.neo4j.kernel.impl.storemigration.StoreFile;
 import org.neo4j.kernel.impl.storemigration.StoreFileType;
 import org.neo4j.kernel.impl.transaction.log.PhysicalLogFile;
 import org.neo4j.test.causalclustering.ClusterRule;
 
 import static org.hamcrest.Matchers.instanceOf;
+import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertThat;
 import static org.junit.Assert.assertTrue;
@@ -49,10 +54,40 @@ public class EnterpriseCoreEditionModuleIntegrationTest
     @Rule
     public ClusterRule clusterRule = new ClusterRule( getClass() );
 
+    private Cluster cluster;
+
+    @After
+    public void tearDown()
+    {
+        EnterpriseCoreEditionModule.idReuse = false;
+    }
+
+    @Test
+    public void createNonBufferedIdComponentsByDefaultWithoutIdReuseCapability() throws Exception
+    {
+        cluster = clusterRule.startCluster();
+        CoreClusterMember leader = cluster.awaitLeader();
+        DependencyResolver dependencyResolver = leader.database().getDependencyResolver();
+
+        IdController idController = dependencyResolver.resolveDependency( IdController.class );
+        IdGeneratorFactory idGeneratorFactory = dependencyResolver.resolveDependency( IdGeneratorFactory.class );
+
+        assertThat( idController, instanceOf( DefaultIdController.class ) );
+        assertThat( idGeneratorFactory, instanceOf( FreeIdFilteredIdGeneratorFactory.class ) );
+
+        IdGenerator idGenerator = idGeneratorFactory.get( IdType.NODE );
+        idGenerator.freeId( 1 );
+        idGenerator.freeId( 2 );
+        idGenerator.freeId( 3 );
+
+        assertEquals( 0, idGenerator.getDefragCount() );
+    }
+
     @Test
-    public void createBufferedIdComponentsByDefault() throws Exception
+    public void createBufferedIdComponentsWhenConfigured() throws Exception
     {
-        Cluster cluster = clusterRule.startCluster();
+        EnterpriseCoreEditionModule.idReuse = true;
+        cluster = clusterRule.startCluster();
         CoreClusterMember leader = cluster.awaitLeader();
         DependencyResolver dependencyResolver = leader.database().getDependencyResolver();