The Leaf Node of ART needs to be shrunk dynamically.

[JigaoLuo]

Found in the comment:

duckdb/src/execution/index/art/leaf.cpp

Line 27 in 7dd852e

//! TODO: Maybe shrink array dynamically?

The leaf node is for the values having the same key. (each prefix byte of the key is the same).
The idea is similar to a C++'s STL std::multimap.
However, it is not clear, how many duplicates can exist in a leaf node.
Thus, the leaf node should dynamically grow and shrink.
(The dynamical grow part is a must and is already implemented.)