Question: Each KV pair has 2 copies in arena?

I'm a C++ beginner, please correct me if I was wrong.
Is it possible to save a pointer to Key rather than a Key object in node?

First copy:
MemTable::Add(): char* buf = arena_.**Allocate**(encoded_len);

Second copy:
template
struct SkipList::Node {
explicit Node(const Key& k) : **key(k)** {}

Key const key;
...
}

Start with MemTable::Add() and the SkipList::Node definition shown in the issue. Trace how the arena-allocated buffer and the node's key are used, including their lifetimes and ownership. Done means establishing whether storing a pointer is safe and documenting the required change or why the existing representation should remain.

Written by the indexing model from the issue text.