Merge #5325

5325: Documents database stats r=irevoire a=ManyTheFish

# Pull Request

## Related issue
Fixes #5319

## List

- Create a DatabaseStats struct
- Compute and store the documents database stats in the IndexStats
- Force dumpless upgrade to update the index stats
- when a document addition/modification/deletion is made, we only recompute the database stats on the added/modified/deleted documents

Co-authored-by: ManyTheFish <many@meilisearch.com>
Co-authored-by: Many the fish <many@meilisearch.com>

crates/index-scheduler/src/index_mapper/mod.rs

@@ -6,6 +6,7 @@ use std::{fs, thread};
 use meilisearch_types::heed::types::{SerdeJson, Str};
 use meilisearch_types::heed::{Database, Env, RoTxn, RwTxn};
 use meilisearch_types::milli;
+use meilisearch_types::milli::database_stats::DatabaseStats;
 use meilisearch_types::milli::update::IndexerConfig;
 use meilisearch_types::milli::{FieldDistribution, Index};
 use serde::{Deserialize, Serialize};
@@ -98,8 +99,9 @@ pub enum IndexStatus {
 /// The statistics that can be computed from an `Index` object.
 #[derive(Serialize, Deserialize, Debug)]
 pub struct IndexStats {
-    /// Number of documents in the index.
-    pub number_of_documents: u64,
+    /// Stats of the documents database.
+    #[serde(default)]
+    pub documents_database_stats: DatabaseStats,
     /// Size taken up by the index' DB, in bytes.
     ///
     /// This includes the size taken by both the used and free pages of the DB, and as the free pages
@@ -138,9 +140,9 @@ impl IndexStats {
     pub fn new(index: &Index, rtxn: &RoTxn) -> milli::Result<Self> {
         let arroy_stats = index.arroy_stats(rtxn)?;
         Ok(IndexStats {
-            number_of_documents: index.number_of_documents(rtxn)?,
             number_of_embeddings: Some(arroy_stats.number_of_embeddings),
             number_of_embedded_documents: Some(arroy_stats.documents.len()),
+            documents_database_stats: index.documents_stats(rtxn)?.unwrap_or_default(),
             database_size: index.on_disk_size()?,
             used_database_size: index.used_size()?,
             primary_key: index.primary_key(rtxn)?.map(|s| s.to_string()),

crates/index-scheduler/src/insta_snapshot.rs

@@ -365,7 +365,8 @@ pub fn snapshot_index_mapper(rtxn: &RoTxn, mapper: &IndexMapper) -> String {
         let stats = mapper.stats_of(rtxn, &name).unwrap();
         s.push_str(&format!(
             "{name}: {{ number_of_documents: {}, field_distribution: {:?} }}\n",
-            stats.number_of_documents, stats.field_distribution
+            stats.documents_database_stats.number_of_entries(),
+            stats.field_distribution
         ));
     }
 

crates/index-scheduler/src/scheduler/test.rs

@@ -910,7 +910,11 @@ fn create_and_list_index() {
         [
           "kefir",
           {
-            "number_of_documents": 0,
+            "documents_database_stats": {
+              "numberOfEntries": 0,
+              "totalKeySize": 0,
+              "totalValueSize": 0
+            },
             "database_size": "[bytes]",
             "number_of_embeddings": 0,
             "number_of_embedded_documents": 0,