Parallel bkt build#443
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MaggieQi merged 2 commits intoMar 18, 2026
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Add BuildTreesParallel() method to BKTree that parallelizes tree construction using a level-order (BFS) approach instead of the existing depth-first recursive method. At each level of the tree, all sibling nodes are processed in parallel using OpenMP, with each thread running independent k-means clustering. The tree structure is then assembled sequentially to maintain correctness. This is controlled by a new ParallelBKTBuild parameter (default: false) that can be enabled in both BKT index and SPANN select-head configurations. Benchmark on SIFT 50M (128-dim, L2) with 32 threads on Azure L32s_v2: - Select Head (BKT build): 16.6 hours -> 1.2 hours (13.6x speedup) - Build Head graph (RefineGraph): unchanged (~10 hours, memory-bound) - Total end-to-end build: ~30 hours -> ~15 hours - Recall@1: 91% -> 94% (slight improvement) - Query latency: comparable (P50 ~40ms)
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* Add parallel BKT tree build support via level-order BFS with OpenMP Add BuildTreesParallel() method to BKTree that parallelizes tree construction using a level-order (BFS) approach instead of the existing depth-first recursive method. At each level of the tree, all sibling nodes are processed in parallel using OpenMP, with each thread running independent k-means clustering. The tree structure is then assembled sequentially to maintain correctness. This is controlled by a new ParallelBKTBuild parameter (default: false) that can be enabled in both BKT index and SPANN select-head configurations. Benchmark on SIFT 50M (128-dim, L2) with 32 threads on Azure L32s_v2: - Select Head (BKT build): 16.6 hours -> 1.2 hours (13.6x speedup) - Build Head graph (RefineGraph): unchanged (~10 hours, memory-bound) - Total end-to-end build: ~30 hours -> ~15 hours - Recall@1: 91% -> 94% (slight improvement) - Query latency: comparable (P50 ~40ms) * change omp to std:::thread --------- Co-authored-by: xufyan <nickyoung.fdu@gmail.com> Co-authored-by: Qi Chen <cheqi@microsoft.com>
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