Opensearch only supports "pre-filtering" or "post-filtering," which leads to either high latency or incomplete results, as explained in the article.
This is why single-stage filtering was the most-requested feature for us.
From the Opensearch docs:
> You should not use approximate k-NN if you want to apply a filter on the index before the k-NN search, which greatly reduces the number of vectors to be searched.
> Because the graphs are constructed during indexing, it is not possible to apply a filter on an index and then use this search method. All filters are applied on the results produced by the approximate nearest neighbor search.
> If you use the knn query alongside filters or other clauses (e.g. bool, must, match), you might receive fewer than k results.
(https://opensearch.org/docs/search-plugins/knn/approximate-k...)
I know Elasticsearch is working on introducing vector search but it is not yet available. I don't know how they will support filtering.
This is why single-stage filtering was the most-requested feature for us.
From the Opensearch docs:
> You should not use approximate k-NN if you want to apply a filter on the index before the k-NN search, which greatly reduces the number of vectors to be searched.
> Because the graphs are constructed during indexing, it is not possible to apply a filter on an index and then use this search method. All filters are applied on the results produced by the approximate nearest neighbor search.
> If you use the knn query alongside filters or other clauses (e.g. bool, must, match), you might receive fewer than k results.
(https://opensearch.org/docs/search-plugins/knn/approximate-k...)
I know Elasticsearch is working on introducing vector search but it is not yet available. I don't know how they will support filtering.