Setting search parameters for one query

Faiss indexes have search parameters as object fields.

However, it can be useful to set these parameters separately per query. For example, for an IndexIVF, one query vector may be run with nprobe=10 and another with nprobe=20. This is problematic when the searches are called from different threads.

To support this use case, a SearchParameter object can be provided as the last argument of the search() function.

SearchParameter instances

Index types that accept search parameters have a corresponding SearchParameter child object. For example, IndexIVFPQ has a SearchParameterIVFPQ object.

The search will look like:

D, I = index.search(xq, 10, params=faiss.SearchParametersIVFPQ(nprobe = 10) 

Note that the params= is mandatory, not to confuse the search parameters with possible I and D output buffers that can also be provided. In C++:

idx_t *I = ...
float *D = ...
faiss::SearchParametersIVFPQ params; 
params.nprobe = 10; 
index.search(nq, xq, 10, D, I, &params);

Searching in a subset of elements