Fix offline tools startup

src/java/org/apache/cassandra/config/DatabaseDescriptor.java

@@ -2899,7 +2899,7 @@ public static Float getMemtableCleanupThreshold()
 
     public static Map<String, String> getMemtableOptions()
     {
-        return conf.memtable;
+        return conf != null ? conf.memtable : null;
     }
 
     public static int getIndexSummaryResizeIntervalInMinutes()

src/java/org/apache/cassandra/db/ColumnFamilyStore.java

@@ -393,10 +393,14 @@ public ColumnFamilyStore(Keyspace keyspace,
 
         logger.info("Initializing {}.{}", keyspace.getName(), name);
 
-        // Create Memtable only on online
+        // Create Memtable and its metrics object only on online
         Memtable initialMemtable = null;
+        TableMetrics.ReleasableMetric memtableMetrics = null;
         if (DatabaseDescriptor.isDaemonInitialized())
+        {
             initialMemtable = createMemtable(new AtomicReference<>(CommitLog.instance.getCurrentPosition()));
+            memtableMetrics = memtableFactory.createMemtableMetrics(metadata);
+        }
         data = new Tracker(this, initialMemtable, loadSSTables);
 
         // Note that this needs to happen before we load the first sstables, or the global sstable tracker will not
@@ -428,7 +432,7 @@ public ColumnFamilyStore(Keyspace keyspace,
             indexManager.addIndex(info, true);
         }
 
-        metric = new TableMetrics(this, memtableFactory.createMemtableMetrics(metadata));
+        metric = new TableMetrics(this, memtableMetrics);
 
         if (data.loadsstables)
         {

src/java/org/apache/cassandra/db/memtable/SkipListMemtable.java

@@ -67,7 +67,7 @@ public class SkipListMemtable extends AbstractAllocatorMemtable
 {
     private static final Logger logger = LoggerFactory.getLogger(SkipListMemtable.class);
 
-    public static final Factory FACTORY = SkipListMemtable::new;
+    public static final Factory FACTORY = SkipListMemtableFactory.INSTANCE;
 
     private static final int ROW_OVERHEAD_HEAP_SIZE;
     static

src/java/org/apache/cassandra/db/memtable/DefaultMemtableFactory.java → src/java/org/apache/cassandra/db/memtable/SkipListMemtableFactory.java

@@ -25,44 +25,20 @@
 import org.apache.cassandra.schema.TableMetadataRef;
 
 /**
- * This class exists solely to avoid initialization of the default memtable class.
- * Some tests want to setup table parameters before initializing DatabaseDescriptor -- this allows them to do so.
+ * This class makes better sense as an inner class to SkipListMemtable (which could be as simple as
+ * FACTORY = SkipListMemtable::new), but having it there causes the SkipListMemtable class to be initialized the first
+ * time it is referenced (e.g. during default memtable factory construction).
+ *
+ * Some tests want to setup table parameters before initializing DatabaseDescriptor -- this allows them to do so, and
+ * also makes sure the memtable memory pools are not created for offline tools.
  */
-public class DefaultMemtableFactory implements Memtable.Factory
+public class SkipListMemtableFactory implements Memtable.Factory
 {
     @Override
     public Memtable create(AtomicReference<CommitLogPosition> commitLogLowerBound, TableMetadataRef metadaRef, Memtable.Owner owner)
     {
-        return SkipListMemtable.FACTORY.create(commitLogLowerBound, metadaRef, owner);
-    }
-
-    @Override
-    public boolean writesShouldSkipCommitLog()
-    {
-        return SkipListMemtable.FACTORY.writesShouldSkipCommitLog();
-    }
-
-    @Override
-    public boolean writesAreDurable()
-    {
-        return SkipListMemtable.FACTORY.writesAreDurable();
-    }
-
-    @Override
-    public boolean streamToMemtable()
-    {
-        return SkipListMemtable.FACTORY.streamToMemtable();
-    }
-
-    @Override
-    public boolean streamFromMemtable()
-    {
-        return SkipListMemtable.FACTORY.streamFromMemtable();
+        return new SkipListMemtable(commitLogLowerBound, metadaRef, owner);
     }
 
-    @Override
-    public TableMetrics.ReleasableMetric createMemtableMetrics(TableMetadataRef metadataRef)
-    {
-        return SkipListMemtable.FACTORY.createMemtableMetrics(metadataRef);
-    }
+    public static final SkipListMemtableFactory INSTANCE = new SkipListMemtableFactory();
 }

src/java/org/apache/cassandra/schema/MemtableParams.java

@@ -26,7 +26,7 @@
 import com.google.common.collect.ImmutableMap;
 
 import org.apache.cassandra.config.DatabaseDescriptor;
-import org.apache.cassandra.db.memtable.DefaultMemtableFactory;
+import org.apache.cassandra.db.memtable.SkipListMemtableFactory;
 import org.apache.cassandra.db.memtable.Memtable;
 import org.apache.cassandra.exceptions.ConfigurationException;
 
@@ -60,7 +60,7 @@ public String toString()
     private MemtableParams()
     {
         this.options = ImmutableMap.of();
-        this.factory = new DefaultMemtableFactory();
+        this.factory = SkipListMemtableFactory.INSTANCE;
     }
 
     public MemtableParams(Map<String, String> options)