[Bug]: range search results are not the same as the intersection of search results with ranges

[yanliang567]

Is there an existing issue for this?

• I have searched the existing issues

Environment

- Milvus version: master-20240425-f06509bf-amd64
- Deployment mode(standalone or cluster): standalone
- MQ type(rocksmq, pulsar or kafka):

Current Behavior

My case is

1. create a collection and insert 10000_128d vectors
2. build index IVF_FLAT with nlist 128, metric=L2
3. load
4. gen a vectorA and get search_res with search for topk=1000
5. radius = search_res[0].distances[350]
   range_filter = search_res[0].distances[50]
6. range search with the same vectorA for topk=300
7. check the range search result with the results of search_res[50:350]

expect:
300 results are same in search_res and range_search_results
actual:
only 51 of range_search_results hit the search_res[50:350], less than 20%

Expected Behavior

if it is hard to get 100% same results with search, it should be >90%

Steps To Reproduce

No response

Milvus Log

test case:

@pytest.mark.tags(CaseLabel.L0)
    @pytest.mark.parametrize("index_type",ct.all_index_types[:6])
    @pytest.mark.parametrize("metric", ct.float_metrics)
    @pytest.mark.parametrize("vector_data_type", ["FLOAT_VECTOR"])
    def test_range_search_default(self, index_type, metric, vector_data_type):
        """
        target: verify the range search returns correct results
        method: 1. create collection, insert 20000 vectors,
                2. search with topk=1000
                3. range search with first 100 distance as filter
                4. verified the range search results is same as the search top 100 results
        """
        collection_w = self.init_collection_general(prefix, auto_id=True, insert_data=False, is_index=False,
                                                    vector_data_type=vector_data_type, with_json=False)[0]
        for _ in range(3):
            data = cf.gen_default_dataframe_data(nb=2000, auto_id=True, with_json=False)
            collection_w.insert(data)

        collection_w.flush()
        _index_params = {"index_type": index_type, "metric_type": metric, "params": cf.get_index_params_params(index_type)}
        collection_w.create_index(ct.default_float_vec_field_name, index_params=_index_params)
        collection_w.load()

        for i in range(2):
            if i % 2 != 0:
                # add some growing segments
                log.debug("verify range search with growing segments")
                for _ in range(2):
                    data = cf.gen_default_dataframe_data(nb=2000, auto_id=True, with_json=False)
                    collection_w.insert(data)

            search_params = {"metric_type": metric, "params": {}}
            nq = 1
            search_vectors = cf.gen_vectors(nq, ct.default_dim)
            search_res = collection_w.search(search_vectors, default_search_field,
                                             search_params, limit=1000)[0]
            # assert len(search_res[0].ids) == 1000
            log.debug(f"search topk=1000 returns {len(search_res[0].ids)}")
            check_topk = 300
            check_from = 30
            ids = search_res[0].ids[check_from:check_from+check_topk]
            radius = search_res[0].distances[check_from+check_topk]
            range_filter = search_res[0].distances[check_from]
            # if metric != "L2":
            #     tmp = radius
            #     radius = range_filter
            #     range_filter = tmp
            range_search_params = {"metric_type": metric, "params": {"radius": radius, "range_filter": range_filter}}
            range_res = collection_w.search(search_vectors, default_search_field,
                                            range_search_params, limit=check_topk)[0]
            range_ids = range_res[0].ids
            log.debug(f"range search radius={radius}, range_filter={range_filter}, results num: {len(range_ids)}")
            hit_rate = round(len(set(ids).intersection(set(range_ids))) / len(set(ids)), 2)
            log.debug(f"range search results hit rate: {hit_rate}")
            assert hit_rate >= 0.9

Anything else?

The same situation with IVF_*, SCCAN Index. HNSW has a better result of 80% hit rate.
Checking the first 10 results, you will see the range_res have better distances

[yanliang567]

/assign @liliu-z
/unassign

[yanliang567]

changed a bit for my test: use FLAT index for the first search and then rebuild the collection with test target index type, the results is a bit better --50%, but still not perfect.

[liliu-z]

Try enlarge range search param

[liliu-z]

/assign @yanliang567

[liliu-z]

/unassign

[yanliang567]

Try enlarge range search param

range search results are already better than search results.
I understand the approaches are different, but I also think we should align the results between search and range search, or it is very confusing to users. @xiaofan-luan @liliu-z
/assign @xiaofan-luan

[yanliang567]

besides, we need to align the results in search, range_search, search with pagination, grouping search, etc.

[liliu-z]

Try enlarge range search param

range search results are already better than search results. I understand the approaches are different, but I also think we should align the results between search and range search, or it is very confusing to users. @xiaofan-luan @liliu-z /assign @xiaofan-luan

@yanliang567 I don't agree about the result alignment

1. search/range are using different algos, it is impossible to do this result alignment
2. I didn't see any necessity to combine the usage of topK search and range search. In that way, we should change range search into topK with distance filtering instead of an independent search type.

Also, we have iterator, search, range search, I didn't see a strong signal that we need to align all the results.

[yanliang567]

@liliu-z From a user’s point of view, he does not care about the algos, he is just confusing about the results are not fitting for each other, and he does not know which results are accurate

[xiaofan-luan]

I think there is no necessity to sync all the search result.
But it does make sense to have at least 90% similar result. Otherwise this may indicate a huge accuracy loss?
@yanliang567 @liliu-z

[liliu-z]

I think there is no necessity to sync all the search result. But it does make sense to have at least 90% similar result. Otherwise this may indicate a huge accuracy loss? @yanliang567 @liliu-z

Yes, we have a param that can be tuned to get better recall

[xiaofan-luan]

let's set the goal to be:

1. default params has more than 90% recall
2. through the knob tuning we can get 95% recall or higher

[yanliang567]

Then we need some improvement here in range search. /assign @liliu-z

[cydrain]

/assign

[cydrain]

[cqy123456]

growing index still not support fp16/bf16/binary vector.

[cqy123456]

plz use this code try again:

@pytest.mark.tags(CaseLabel.L0)
@pytest.mark.parametrize("vector_data_type", ct.all_float_vector_types)
@pytest.mark.parametrize("with_growing", [True, False])
def test_range_search_default(self, index_type, metric, vector_data_type, with_growing):
    """
    target: verify the range search returns correct results
    method: 1. create collection, insert 8000 vectors,
            2. search with topk=1000
            3. range search from the 30th-330th distance as filter
            4. verified the range search results is same as the search results in the range
    """
    counter = 0
    collection_w = self.init_collection_general(prefix, auto_id=True, insert_data=False, is_index=False,
                                                vector_data_type=vector_data_type, with_json=False)[0]
    nb = 2000
    for i in range(3):
        data = cf.gen_general_default_list_data(nb=nb, auto_id=True, start=counter,
                                                vector_data_type=vector_data_type, with_json=False)
        collection_w.insert(data)
        counter = counter + nb

    collection_w.flush()
    _index_params = {"index_type": "FLAT", "metric_type": metric, "params": {}}
    collection_w.create_index(ct.default_float_vec_field_name, index_params=_index_params)
    collection_w.load()

    if with_growing is True:
        # add some growing segments
        for _ in range(2):
            data = cf.gen_general_default_list_data(nb=nb, auto_id=True, start=counter,
                                                    vector_data_type=vector_data_type, with_json=False)
            collection_w.insert(data)
            counter = counter + nb

    search_params = {"params": {}}
    nq = 1
    search_vectors = cf.gen_vectors(nq, ct.default_dim, vector_data_type=vector_data_type)
    search_res = collection_w.search(search_vectors, default_search_field,
                                        search_params, limit=1000)[0]
    assert len(search_res[0].ids) == 1000
    log.debug(f"search topk=1000 returns {len(search_res[0].ids)}")
    check_topk = 300
    check_from = 30
    ids = search_res[0].ids[check_from:check_from + check_topk]
    radius = search_res[0].distances[check_from + check_topk]
    range_filter = search_res[0].distances[check_from]

    # rebuild the collection with test target index
    collection_w.release()
    collection_w.indexes[0].drop()
    _index_params = {"index_type": index_type, "metric_type": metric,
                        "params": cf.get_index_params_params(index_type)}
    collection_w.create_index(ct.default_float_vec_field_name, index_params=_index_params)
    collection_w.load()

    params = cf.get_search_params_params(index_type)
    params.update({"radius": radius, "range_filter": range_filter})
    if index_type == "HNSW":
        params.update({"ef": check_topk+100})
    if index_type == "IVF_PQ":
        params.update({"max_empty_result_buckets": 100})
    range_search_params = {"params": params}
    range_res = collection_w.search(search_vectors, default_search_field,
                                    range_search_params, limit=check_topk)[0]
    range_ids = range_res[0].ids
    # assert len(range_ids) == check_topk
    log.debug(f"cqy: index params: _index_params{_index_params}")
    log.debug(f"cqy: knn ids={ids}")
    log.debug(f"cqy: knn dis={search_res[0].distances[check_from:check_from + check_topk]}")
    log.debug(f"cqy: range_search ids={range_res[0].ids}")
    log.debug(f"cqy: range_search dis={range_res[0].distances}")
    log.debug(f"cqy: range search radius={radius}, range_filter={range_filter}, range results num: {len(range_ids)}")
    hit_rate = round(len(set(ids).intersection(set(range_ids))) / len(set(ids)), 2)
    log.debug(f"cqy: range search results with growing {with_growing} hit rate: {hit_rate}")
    assert hit_rate >= 0.2    # issue #32630 to improve the accuracy

[cqy123456]

test case in milvus may has some problem. when i = 1, use current index to generate gt, instead of flat.

[cydrain]

some errors in the test script:

1. in line 6912 and 6926, "cf.gen_general_default_list_data" is called to generate test data, but this API always generates id from 0 by default, should change it like following:

    row_cnt = 0
    nb = 2000
    for i in range(3):
        data = cf.gen_general_default_list_data(nb=nb, auto_id=True, start=row_cnt,
                                                vector_data_type=vector_data_type, with_json=False)
        collection_w.insert(data)
        row_cnt += nb

2. in the 1st loop, "FLAT" index is dropped and new specified index is created, so in the 2nd loop, this new created index is used to calculate the golden, and makes the recall calculation meaningless.

this test script need update @yanliang567

[cydrain]

/assign @yanliang567

[yanliang567]

updating and rerunning the tests...