Optimizer (Tune)

For graph-based indexes (HNSW, HGraph), VSAG exposes the Tune interface, which automatically adjusts runtime parameters based on a representative query set to get a better trade-off between recall and latency. Internally this is the historical “ELP Optimizer”.

Basic Usage

#include <vsag/vsag.h>

auto index = vsag::Factory::CreateIndex("hgraph", build_params).value();
index->Build(base_dataset);

std::string tune_params = R"(
{
    "queries_dataset": "path/or/inline/queries",
    "target_recall": 0.95,
    "top_k": 10
}
)";
auto ret = index->Tune(tune_params);

The second argument disable_future_tuning defaults to false, allowing repeated calls to keep refining. Set it to true to freeze the parameters.

Relationship with the ELP Optimizer

Older literature (see Research Papers) refers to the “ELP Optimizer”. Its implementation key is use_elp_optimizer, which now lives behind the unified Tune API — users no longer need to flip it directly.

Supported Indexes

Example

examples/cpp/318_feature_tune.cpp walks through an end-to-end tuning flow:

1. Create the index and Build.
2. Call Tune with a representative query set.
3. Serialize the tuned index for production use.

Notes

• Tuning is sensitive to the query distribution — use samples that reflect real traffic.
• Tuned parameters are persisted together with the index metadata via Serialize/Deserialize and remain in effect after deployment.