Serialization

VSAG indexes can be serialized and deserialized through several interfaces, supporting persistence, cross-process sharing, and distributed deployment.

Three Interfaces

1. BinarySet / ReaderSet

The most flexible option. The index is split into named binary segments, and the caller owns the storage medium (object store, KV, sharded uploads, etc.).

// Save
vsag::BinarySet bs = index->Serialize().value();
for (const auto& key : bs.GetKeys()) {
    auto binary = bs.Get(key);
    // Write to storage
}

// Load
vsag::BinarySet bs_loaded;
// Populate bs_loaded by reading each key from storage.
auto empty = vsag::Factory::CreateIndex("hnsw", build_params).value();
empty->Deserialize(bs_loaded);

ReaderSet is similar to BinarySet but uses a user-supplied Reader to read on demand, which avoids loading everything at once. This is useful for memory-constrained or partial-deserialization scenarios (for example, the on-disk portion of DiskANN).

2. File Streams (std::ostream / std::istream)

The simplest option — serialize the whole index to a file or memory stream:

std::ofstream out("index.bin", std::ios::binary);
index->Serialize(out);

std::ifstream in("index.bin", std::ios::binary);
empty->Deserialize(in);

3. Custom Write Function (WriteFuncType)

For streaming or chunked backends, supply a write callback:

index->Serialize([&](const void* buf, uint64_t offset, uint64_t size) {
    // Write [buf, buf+size) at offset
});

Notes

• Deserialize requires an empty target index whose configuration (dim, metric_type, etc.) matches the one used at serialization time.
• When upgrading across major versions, check the compatibility notes in the release notes.
• DiskANN’s disk files are managed independently; Serialize returns the in-memory metadata side.
• References: examples/cpp/318_feature_tune.cpp, examples/cpp/401_persistent_kv.cpp, examples/cpp/402_persistent_streaming.cpp.