# Hybrid Search: Pagination Best Practices **URL:** \ **Category:** OpenSearch\ **Created:** [February 24, 2025, 10:50am UTC](https://forum.opensearch.org/t/hybrid-search-pagination-best-practices/23545 "2025-02-24T10:50:12Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![tobe](https://avatars.discourse-cdn.com/v4/letter/t/8e7dd6/32.png) [@tobe](https://forum.opensearch.org/u/tobe)\ **Post date:** [February 24, 2025, 10:50am UTC](https://forum.opensearch.org/t/hybrid-search-pagination-best-practices/23545/1 "2025-02-24T10:50:12Z")
**Versions** (relevant - OpenSearch/Dashboard/Server OS/Browser): 2.19 **Describe the issue** : With 2.19, a new parameter `pagination_depth` has been introduced, see [#1048](https://github.com/opensearch-project/neural-search/pull/1048). I am now wondering about the meaning of this parameter in the practical sense. I understood from the docs that it limits the number of results retrieved from each shard per subquery before anything else happens like filtering, score normalisation etc., see the [docs](https://opensearch.org/docs/latest/search-plugins/hybrid-search/#the-impact-of-pagination_depth-on-hybrid-search-results). So I made a small experiment with a hybrid query for one index (shard), setting `pagination_depth` to 1. This gives me 2 results since each subquery is limited to one result. So if I want the client to be able to page through a long list of results, I’d have to set `pagination_depth` to a very high value (i.e. the expected max. number of results for one subquery) since it represents the number of documents from which a portion (i.e. a page) would be returned? In general, I try to use `search_after` because of performance reasons and the limitation of pagination with `from` to 10’000 results. This is also possible for hybrid search but the sorting criteria cannot combine `_score` with another field like `_id` to make this deterministic even if two docs would have the same score: `_score sort criteria cannot be applied with any other criteria. Please select one sort criteria out of them.` I understand that this is the overall score calculated from the two subqueries’ scores. So it comes down to two questions: - Is my understanding of `pagination_depth` correct? - Is there a way to make sorting with `search_after` deterministic without ignoring the score? **Configuration** : **Relevant Logs or Screenshots** : ---
**Author:** ![nateynate](https://sea1.discourse-cdn.com/flex019/user_avatar/forum.opensearch.org/nateynate/32/4913_2.png) [@nateynate](https://forum.opensearch.org/u/nateynate)\ **Post date:** [February 24, 2025, 8:12pm UTC](https://forum.opensearch.org/t/hybrid-search-pagination-best-practices/23545/2 "2025-02-24T20:12:08Z")
Hi @tobe - I tapped Varun on the shoulder to see if he could add a helpful reply here. Outside of that, this actually might be a good question to put into GitHub as an issue or even a comment on the PR itself. Plenty of devs there might have different takes on it. ---
**Author:** ![varun4996](https://avatars.discourse-cdn.com/v4/letter/v/ba9def/32.png) [@varun4996](https://forum.opensearch.org/u/varun4996)\ **Post date:** [February 27, 2025, 7:03pm UTC](https://forum.opensearch.org/t/hybrid-search-pagination-best-practices/23545/3 "2025-02-27T19:03:10Z")
**What is `pagination_depth`?** `Pagination_depth` defines the count of top search results of each sub-query from every shard need to picked for hybridization. The reason why this parameter is introduced is because earlier when you increase the `size` and `from` then the result ordering use to get changed because of normalization and combination. **Context around why `pagination_depth` is introduced:** For standard hybrid search without pagination, it always uses `from+size` formula to capture search results of each subquery from every individual shard where from =0 and size (what user provides). The challenge here is when you increase the from and size values to see more results then new results captured might end up on earlier pages because after normalization then can be ranked higher depending on weights. Therefore, it will change the ground\_truth on which user is pagination. What does **pagination\_depth** do? As we have a ground\_truth disruption issue discussed earlier while applying pagination with `from` and `size`, therefore to counter that we introduced a new parameter called `pagination_depth`. This parameter essentially gives user an ability to decide how many search results they need to consider from each shard to hybridize and set the search results reference on which they can paginate consistently. Then by using `from` and `size` they can navigate on that search result reference. For example: Consider an index with 3 shards. A user performs a hybrid search which contains two subqueries: match and knn. User provided from = 10, size = 30 and pagination\_depth=20. For match query, it can capture up-to `pagination_depth x number of shards` equivalent number of results. Provided every shard does have that many results. In this case it can capture up-to 20 x 3 =60. Now consider every shard does have that many results for match query, so coordinator node got 60 results for match query. Similarly for k-nn query, coordinator node can recieve upto 60 results. 60 + 60 = 120 results. Out of 120 results lets consider 50 results are common for both match and knn query After normalization and combination the total result count will be 120-50 = 70 So by using `pagination_depth = 20` user ends up getting 70 unique hybridized search results. Now from was 10 and size was 30 so it will return result according from those 70 documents. I hope that makes things clear. ---
**Author:** ![tobe](https://avatars.discourse-cdn.com/v4/letter/t/8e7dd6/32.png) [@tobe](https://forum.opensearch.org/u/tobe)\ **Post date:** [March 3, 2025, 8:56am UTC](https://forum.opensearch.org/t/hybrid-search-pagination-best-practices/23545/4 "2025-03-03T08:56:03Z")
Hi @varun4996 and @nateynate, Thanks a lot for clarifying this. What about pagination with `search_after`? I noticed that it is possible to use it with hybrid search (see [docs](https://opensearch.org/docs/latest/search-plugins/hybrid-search/#hybrid-search-with-search_after)) but it is not possible to combine `_sort` with another criterion like `_id` to make this deterministic: `_score sort criteria cannot be applied with any other criteria. Please select one sort criteria out of them.` I understand that the cursor refers to the resulting list _after_ normalisation and I wonder if this leads to similar issues like with offset-based pagination (the ground truth issue). Is this the reason for this limitation and if yes are you planning on finding a solution for this as well? ---
**Author:** ![varun4996](https://avatars.discourse-cdn.com/v4/letter/v/ba9def/32.png) [@varun4996](https://forum.opensearch.org/u/varun4996)\ **Post date:** [March 3, 2025, 6:42pm UTC](https://forum.opensearch.org/t/hybrid-search-pagination-best-practices/23545/5 "2025-03-03T18:42:26Z")
@tobe please checkout this blog [How sorting works in hybrid queries · OpenSearch](https://opensearch.org/blog/Internal-functioning-of-sorting-in-hybrid-query/). In this blog, I have explained it in proper way that why `_score` sort criteria cannot be applied with any other criteria.