RDDT: Group-by loop on proxy - #20
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Details
Reduce filter + group-by latency from ~800 ms to ~40 ms (20× faster) by rewriting the group-by execution logic in Milvus.
• Context: A search request needs at least k groups with m docs per group (e.g. 15 groups × 1 doc)..
• Before: Every segment used the ANN iterator to independently find all required groups, which meant a lot of redundant work..
• Now: Each segment just runs a normal HNSW search and returns whatever groups it finds. The proxy merges the results, and only if there still aren't enough unique groups does it issue another round, excluding groups/docs that were already returned..
For example, if one segment returns 10 groups and another returns 5 different groups, the proxy already has the required 15 groups, so there's no need for every segment to find all 15.
• Trade-off: This may reduce recall slightly in some cases, but the nearest groups are still accurate in practice. We can also make the behavior configurable to allow more iterations when higher recall is preferred..
Tests