@Override
        public synchronized void close() {
            if (closeCallback == null) {
                throw new IllegalStateException("RocksDBDualCFIterator expects close callback to be set immediately upon creation");
            }
            closeCallback.run();

            iterNoTimestamp.close();
            iterWithTimestamp.close();
            open = false;
        }
A persistent key-(value-timestamp) store based on RocksDB.
streams/src/main/java/org/apache/kafka/streams/state/internals/RocksDBTimestampedStore.java