Merge #4140

4140: Fix bug where search with distinct attribute has wrong totalHits and totalPages r=dureuill a=vivek-26

# Pull Request

## Related issue
Fixes #4130

## What does this PR do?
This PR - 
- Fixes the bug where search with distinct attribute and pagination (no ranking) returns incorrect values for `totalHits` and `totalPages`.
- Add/update unit and integration tests.

## PR checklist
Please check if your PR fulfills the following requirements:
- [x] Does this PR fix an existing issue, or have you listed the changes applied in the PR description (and why they are needed)?
- [x] Have you read the contributing guidelines?
- [x] Have you made sure that the title is accurate and descriptive of the changes?

Thank you so much for contributing to Meilisearch!


Co-authored-by: Vivek Kumar <vivek.26@outlook.com>
Co-authored-by: Louis Dureuil <louis.dureuil@gmail.com>

meilisearch/tests/search/distinct.rs

@@ -6,21 +6,109 @@ use crate::common::Server;
 
 pub(self) static DOCUMENTS: Lazy<Value> = Lazy::new(|| {
     json!([
-        {"productId": 1, "shopId": 1},
-        {"productId": 2, "shopId": 1},
-        {"productId": 3, "shopId": 2},
-        {"productId": 4, "shopId": 2},
-        {"productId": 5, "shopId": 3},
-        {"productId": 6, "shopId": 3},
-        {"productId": 7, "shopId": 4},
-        {"productId": 8, "shopId": 4},
-        {"productId": 9, "shopId": 5},
-        {"productId": 10, "shopId": 5}
+      {
+        "id": 1,
+        "description": "Leather Jacket",
+        "brand": "Lee Jeans",
+        "product_id": "123456",
+        "color": "Brown"
+      },
+      {
+        "id": 2,
+        "description": "Leather Jacket",
+        "brand": "Lee Jeans",
+        "product_id": "123456",
+        "color": "Black"
+      },
+      {
+        "id": 3,
+        "description": "Leather Jacket",
+        "brand": "Lee Jeans",
+        "product_id": "123456",
+        "color": "Blue"
+      },
+      {
+        "id": 4,
+        "description": "T-Shirt",
+        "brand": "Nike",
+        "product_id": "789012",
+        "color": "Red"
+      },
+      {
+        "id": 5,
+        "description": "T-Shirt",
+        "brand": "Nike",
+        "product_id": "789012",
+        "color": "Blue"
+      },
+      {
+        "id": 6,
+        "description": "Running Shoes",
+        "brand": "Adidas",
+        "product_id": "456789",
+        "color": "Black"
+      },
+      {
+        "id": 7,
+        "description": "Running Shoes",
+        "brand": "Adidas",
+        "product_id": "456789",
+        "color": "White"
+      },
+      {
+        "id": 8,
+        "description": "Hoodie",
+        "brand": "Puma",
+        "product_id": "987654",
+        "color": "Gray"
+      },
+      {
+        "id": 9,
+        "description": "Sweater",
+        "brand": "Gap",
+        "product_id": "234567",
+        "color": "Green"
+      },
+      {
+        "id": 10,
+        "description": "Sweater",
+        "brand": "Gap",
+        "product_id": "234567",
+        "color": "Red"
+      },
+      {
+        "id": 11,
+        "description": "Sweater",
+        "brand": "Gap",
+        "product_id": "234567",
+        "color": "Blue"
+      },
+      {
+        "id": 12,
+        "description": "Jeans",
+        "brand": "Levi's",
+        "product_id": "345678",
+        "color": "Indigo"
+      },
+      {
+        "id": 13,
+        "description": "Jeans",
+        "brand": "Levi's",
+        "product_id": "345678",
+        "color": "Black"
+      },
+      {
+        "id": 14,
+        "description": "Jeans",
+        "brand": "Levi's",
+        "product_id": "345678",
+        "color": "Stone Wash"
+      }
     ])
 });
 
-pub(self) static DOCUMENT_PRIMARY_KEY: &str = "productId";
-pub(self) static DOCUMENT_DISTINCT_KEY: &str = "shopId";
+pub(self) static DOCUMENT_PRIMARY_KEY: &str = "id";
+pub(self) static DOCUMENT_DISTINCT_KEY: &str = "product_id";
 
 /// testing: https://github.com/meilisearch/meilisearch/issues/4078
 #[actix_rt::test]
@@ -33,31 +121,121 @@ async fn distinct_search_with_offset_no_ranking() {
     index.update_distinct_attribute(json!(DOCUMENT_DISTINCT_KEY)).await;
     index.wait_task(1).await;
 
-    fn get_hits(response: Value) -> Vec<i64> {
+    fn get_hits(response: &Value) -> Vec<&str> {
         let hits_array = response["hits"].as_array().unwrap();
-        hits_array.iter().map(|h| h[DOCUMENT_DISTINCT_KEY].as_i64().unwrap()).collect::<Vec<_>>()
+        hits_array.iter().map(|h| h[DOCUMENT_DISTINCT_KEY].as_str().unwrap()).collect::<Vec<_>>()
     }
 
-    let (response, code) = index.search_post(json!({"limit": 2, "offset": 0})).await;
-    let hits = get_hits(response);
+    let (response, code) = index.search_post(json!({"offset": 0, "limit": 2})).await;
+    let hits = get_hits(&response);
     snapshot!(code, @"200 OK");
     snapshot!(hits.len(), @"2");
-    snapshot!(format!("{:?}", hits), @"[1, 2]");
+    snapshot!(format!("{:?}", hits), @r#"["123456", "789012"]"#);
+    snapshot!(response["estimatedTotalHits"] , @"11");
 
-    let (response, code) = index.search_post(json!({"limit": 2, "offset": 2})).await;
-    let hits = get_hits(response);
+    let (response, code) = index.search_post(json!({"offset": 2, "limit": 2})).await;
+    let hits = get_hits(&response);
     snapshot!(code, @"200 OK");
     snapshot!(hits.len(), @"2");
-    snapshot!(format!("{:?}", hits), @"[3, 4]");
+    snapshot!(format!("{:?}", hits), @r#"["456789", "987654"]"#);
+    snapshot!(response["estimatedTotalHits"], @"10");
 
-    let (response, code) = index.search_post(json!({"limit": 10, "offset": 4})).await;
-    let hits = get_hits(response);
+    let (response, code) = index.search_post(json!({"offset": 4, "limit": 2})).await;
+    let hits = get_hits(&response);
+    snapshot!(code, @"200 OK");
+    snapshot!(hits.len(), @"2");
+    snapshot!(format!("{:?}", hits), @r#"["234567", "345678"]"#);
+    snapshot!(response["estimatedTotalHits"], @"6");
+
+    let (response, code) = index.search_post(json!({"offset": 5, "limit": 2})).await;
+    let hits = get_hits(&response);
     snapshot!(code, @"200 OK");
     snapshot!(hits.len(), @"1");
-    snapshot!(format!("{:?}", hits), @"[5]");
+    snapshot!(format!("{:?}", hits), @r#"["345678"]"#);
+    snapshot!(response["estimatedTotalHits"], @"6");
 
-    let (response, code) = index.search_post(json!({"limit": 10, "offset": 5})).await;
-    let hits = get_hits(response);
+    let (response, code) = index.search_post(json!({"offset": 6, "limit": 2})).await;
+    let hits = get_hits(&response);
     snapshot!(code, @"200 OK");
     snapshot!(hits.len(), @"0");
+    snapshot!(format!("{:?}", hits), @r#"[]"#);
+    snapshot!(response["estimatedTotalHits"], @"6");
+
+    let (response, code) = index.search_post(json!({"offset": 7, "limit": 2})).await;
+    let hits = get_hits(&response);
+    snapshot!(code, @"200 OK");
+    snapshot!(hits.len(), @"0");
+    snapshot!(format!("{:?}", hits), @r#"[]"#);
+    snapshot!(response["estimatedTotalHits"], @"6");
+}
+
+/// testing: https://github.com/meilisearch/meilisearch/issues/4130
+#[actix_rt::test]
+async fn distinct_search_with_pagination_no_ranking() {
+    let server = Server::new().await;
+    let index = server.index("test");
+
+    let documents = DOCUMENTS.clone();
+    index.add_documents(documents, Some(DOCUMENT_PRIMARY_KEY)).await;
+    index.update_distinct_attribute(json!(DOCUMENT_DISTINCT_KEY)).await;
+    index.wait_task(1).await;
+
+    fn get_hits(response: &Value) -> Vec<&str> {
+        let hits_array = response["hits"].as_array().unwrap();
+        hits_array.iter().map(|h| h[DOCUMENT_DISTINCT_KEY].as_str().unwrap()).collect::<Vec<_>>()
+    }
+
+    let (response, code) = index.search_post(json!({"page": 0, "hitsPerPage": 2})).await;
+    let hits = get_hits(&response);
+    snapshot!(code, @"200 OK");
+    snapshot!(hits.len(), @"0");
+    snapshot!(format!("{:?}", hits), @r#"[]"#);
+    snapshot!(response["page"], @"0");
+    snapshot!(response["totalPages"], @"3");
+    snapshot!(response["totalHits"], @"6");
+
+    let (response, code) = index.search_post(json!({"page": 1, "hitsPerPage": 2})).await;
+    let hits = get_hits(&response);
+    snapshot!(code, @"200 OK");
+    snapshot!(hits.len(), @"2");
+    snapshot!(format!("{:?}", hits), @r#"["123456", "789012"]"#);
+    snapshot!(response["page"], @"1");
+    snapshot!(response["totalPages"], @"3");
+    snapshot!(response["totalHits"], @"6");
+
+    let (response, code) = index.search_post(json!({"page": 2, "hitsPerPage": 2})).await;
+    let hits = get_hits(&response);
+    snapshot!(code, @"200 OK");
+    snapshot!(hits.len(), @"2");
+    snapshot!(format!("{:?}", hits), @r#"["456789", "987654"]"#);
+    snapshot!(response["page"], @"2");
+    snapshot!(response["totalPages"], @"3");
+    snapshot!(response["totalHits"], @"6");
+
+    let (response, code) = index.search_post(json!({"page": 3, "hitsPerPage": 2})).await;
+    let hits = get_hits(&response);
+    snapshot!(code, @"200 OK");
+    snapshot!(hits.len(), @"2");
+    snapshot!(format!("{:?}", hits), @r#"["234567", "345678"]"#);
+    snapshot!(response["page"], @"3");
+    snapshot!(response["totalPages"], @"3");
+    snapshot!(response["totalHits"], @"6");
+
+    let (response, code) = index.search_post(json!({"page": 4, "hitsPerPage": 2})).await;
+    let hits = get_hits(&response);
+    snapshot!(code, @"200 OK");
+    snapshot!(hits.len(), @"0");
+    snapshot!(format!("{:?}", hits), @r#"[]"#);
+    snapshot!(response["page"], @"4");
+    snapshot!(response["totalPages"], @"3");
+    snapshot!(response["totalHits"], @"6");
+
+    let (response, code) = index.search_post(json!({"page": 2, "hitsPerPage": 3})).await;
+    let hits = get_hits(&response);
+    snapshot!(code, @"200 OK");
+    snapshot!(hits.len(), @"3");
+    snapshot!(format!("{:?}", hits), @r#"["987654", "234567", "345678"]"#);
+    snapshot!(response["page"], @"2");
+    snapshot!(response["totalPages"], @"2");
+    snapshot!(response["totalHits"], @"6");
 }

milli/src/search/new/bucket_sort.rs

@@ -46,9 +46,8 @@ pub fn bucket_sort<'ctx, Q: RankingRuleQueryTrait>(
         if let Some(distinct_fid) = distinct_fid {
             let mut excluded = RoaringBitmap::new();
             let mut results = vec![];
-            let mut skip = 0;
             for docid in universe.iter() {
-                if results.len() >= length {
+                if results.len() >= from + length {
                     break;
                 }
                 if excluded.contains(docid) {
@@ -56,16 +55,19 @@ pub fn bucket_sort<'ctx, Q: RankingRuleQueryTrait>(
                 }
 
                 distinct_single_docid(ctx.index, ctx.txn, distinct_fid, docid, &mut excluded)?;
-                skip += 1;
-                if skip <= from {
-                    continue;
-                }
-
                 results.push(docid);
             }
 
             let mut all_candidates = universe - excluded;
             all_candidates.extend(results.iter().copied());
+            // drain the results of the skipped elements
+            // this **must** be done **after** writing the entire results in `all_candidates` to ensure
+            // e.g. estimatedTotalHits is correct.
+            if results.len() >= from {
+                results.drain(..from);
+            } else {
+                results.clear();
+            }
 
             return Ok(BucketSortOutput {
                 scores: vec![Default::default(); results.len()],

milli/tests/search/distinct.rs

@@ -202,7 +202,7 @@ test_distinct!(
     EXTERNAL_DOCUMENTS_IDS.len(),
     1,
     vec![],
-    2
+    3
 );
 test_distinct!(
     // testing: https://github.com/meilisearch/meilisearch/issues/4078
@@ -212,7 +212,7 @@ test_distinct!(
     1,
     2,
     vec![],
-    1
+    3
 );
 test_distinct!(
     // testing: https://github.com/meilisearch/meilisearch/issues/4078
@@ -222,7 +222,7 @@ test_distinct!(
     EXTERNAL_DOCUMENTS_IDS.len(),
     2,
     vec![],
-    5
+    7
 );
 test_distinct!(
     // testing: https://github.com/meilisearch/meilisearch/issues/4078
@@ -232,5 +232,5 @@ test_distinct!(
     2,
     4,
     vec![],
-    3
+    7
 );