Module art_node 

ART (Adaptive Radix Tree) node types with arena allocation.

Four node sizes matching the C++ ART implementation:

• Node4: Up to 4 children — smallest, best for sparse branches
• Node16: Up to 16 children — transitions from Node4 at 5 children
• Node48: Up to 48 children — uses indirect index for compact storage
• Node256: Up to 256 children — full fan-out, direct array

Each node carries:

• A prefix (compressed path from parent)
• A set of offsets (row IDs stored at this leaf)
• overflow_offsets (additional row IDs for duplicate keys)

Port of C++ ArtPrimaryKeyIndex::Node from art_index.h (lines 95–145) and art_index.cpp.

Structs

NodeBlock

A block of nodes in contiguous memory, used for arena allocation.

Enums

ArtNode

An ART node — stores a prefix, child pointers, and value offsets.

NodeKind

ART node kind.

Constants

EMPTY_MARKER

Marker for unused child slots in Node48’s indirect index.

NODE4_MAX

The growth threshold from one node type to the next.

NODE16_MAX

NODE48_MAX

NODE_BLOCK_CAPACITY

Maximum number of nodes per arena block.