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Default parameters for the GPU nearest neighbour backends

params_knn_gpu_defaults.Rd

GPU sibling of bixverse::params_knn_defaults(). The GPU indices take a different knob set: there is no Annoy and no HNSW on the device, so what survives is exhaustive, IVF and NN-descent.

Usage

params_knn_gpu_defaults()

Value

A named list with the following elements:

  • k - Integer. Number of neighbours. 0L hands the choice to Rust, which uses sqrt(n_cells) * 0.5 and then adjusts for the simulated doublets. Defaults to 15L.

  • knn_method - String. The GPU index to use. One of c("exhaustive", "ivf", "nndescent"). Defaults to "exhaustive".

  • ann_dist - String. Manhattan is not supported by the GPU kernels. One of c("euclidean", "cosine"). Defaults to "euclidean".

  • n_list - Integer or NULL. IVF only. Number of clusters. NULL gives sqrt(n). Defaults to NULL.

  • n_probe - Integer or NULL. IVF only. Clusters to probe. NULL gives sqrt(n_list). Defaults to NULL.

  • graph_k - Integer or NULL. NN-descent only. Node degree of the graph after pruning. NULL gives 30, widened to cover k when extract_knn is set. Defaults to NULL.

  • k_build - Integer or NULL. NN-descent only. Build degree before pruning. NULL gives max(k, floor(1.5 * k)). Defaults to NULL.

  • n_tree - Integer or NULL. NN-descent only. Trees seeding the descent. Defaults to NULL.

  • delta - Numeric. NN-descent only. Termination criterium for the descent. Defaults to 0.001.

  • rho - Numeric or NULL. NN-descent only. Sampling rate for the descent. Defaults to NULL.

  • refine_knn - Integer or NULL. NN-descent only. 2-hop refinement sweeps after the descent. Buys graph quality at a linear cost. NULL gives 0. Defaults to NULL.

  • beam_width - Integer or NULL. NN-descent only. Beam width when querying. Ignored when extract_knn is set. Defaults to NULL.

  • max_beam_iters - Integer or NULL. NN-descent only. Beam search iterations. Ignored when extract_knn is set. Defaults to NULL.

  • n_entry_points - Integer or NULL. NN-descent only. Entry points when querying. Ignored when extract_knn is set. Defaults to NULL.

  • extract_knn - Boolean. NN-descent only. Hand back the graph the descent built instead of beam searching over it. Defaults to FALSE.

Details

NN-descent builds a CAGRA graph and, with extract_knn = TRUE, hands that graph back rather than beam searching over it. Note that this saves the query, not the build: the descent itself dominates, and its build degree tracks k. NN-descent is therefore a low-k tool on the GPU. Above k of roughly 30 both exhaustive and IVF beat it, and by k = 200 they beat it by more than an order of magnitude.