CSR Index

CSR (Compressed Sparse Row) is the graph engine's core index format. It stores adjacency data in contiguous arrays for cache-resident traversal.

Layout

out_offsets: Vec<u32>        [num_nodes + 1]  — offset into target array per node
out_targets: DenseArray<u32> [num_edges]      — destination node IDs (contiguous, mmap-capable)
out_labels:  DenseArray<u16> [num_edges]      — edge labels (parallel array)
out_weights: Option<DenseArray<f64>>           — optional, allocated only when weighted

in_offsets / in_targets / in_labels / in_weights — symmetric for inbound

Memory Efficiency

At 1 billion edges, CSR uses ~10 GB vs ~60 GB for naive adjacency lists (6x improvement). Node IDs are interned as u32, labels as u16.

Storage

Edges are persisted in a redb B-Tree with forward and reverse indexes. The CSR index is built at query time for bulk operations. Writes go to a mutable buffer and become visible immediately. Compaction merges the buffer into dense CSR arrays when the buffer exceeds 10% of the dense size.

Graph Operations

The CSR index supports all traversal and algorithm operations:

• BFS/DFS traversal
• Shortest path (Dijkstra)
• All 13 native graph algorithms
• MATCH pattern matching
• GraphRAG fusion