Andrew Kyle Purtell created PHOENIX-8009:
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             Summary: Vector Indexes Phase 2
                 Key: PHOENIX-8009
                 URL: https://issues.apache.org/jira/browse/PHOENIX-8009
             Project: Phoenix
          Issue Type: Sub-task
            Reporter: Andrew Kyle Purtell
            Assignee: Andrew Kyle Purtell


The IVF algorithm delivered in PHOENIX-7998 provides effective approximate 
nearest-neighbor search by partitioning high dimensional space into Voronoi 
cells, but its cluster-centric design imposes recall limitations under high 
dimensional skew and requires periodic centroid retraining as data 
distributions shift. Hierarchical Navigable Small World (HNSW) graph indexes 
can deliver higher recall at equivalent query latency and achieve two-fold to 
five-fold recall improvements over IVF at equivalent latency budgets by 
introducing a graph-based ANN algorithm alongside the existing IVF algorithm. 
This capability targets similarity search queries where high recall is 
paramount, update heavy workloads where IVF centroid drift degrades quality 
between rebuild cycles, and moderate scale vector collections where the memory 
footprint remains tractable.

Algorithmic foundations draw from the HNSW construction algorithm formalized by 
Malkov and Yashunin in 2018 combined with the Vamana robust pruning heuristic 
from the DiskANN work by Subramanya et al. in 2019, adapted to Phoenix's 
distributed coprocessor execution model and HBase storage semantics. Integrated 
vector quantization draws from scalar quantization and product quantization 
formalized by Jégou, Douze, and Schmid in 2011, fused directly into the graph 
storage layout and search pipeline to minimize block cache pressure and I/O 
amplification during graph traversal.



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