private void throwIfClosed() {
    if (closed.get()) {
      LOG.error("Attempting to use a closed RocksDBKeyValueStorage");
      throw new IllegalStateException("Storage has been closed");
    }
  }
Instantiates a new RocksDb columnar key value snapshot.

@param db the db
@param metrics the metrics
plugins/rocksdb/src/main/java/org/hyperledger/besu/plugin/services/storage/rocksdb/segmented/RocksDBColumnarKeyValueSnapshot.java