update the test with the stats

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

@@ -19,8 +19,18 @@ impl IndexScheduler {
                 indexes.len() as u32,
             ));
             let index = self.index(uid)?;
-            milli::update::upgrade::upgrade(&index, progress.clone())
+            let mut wtxn = index.write_txn()?;
+            let regenerate = milli::update::upgrade::upgrade(&mut wtxn, &index, progress.clone())
                 .map_err(|e| Error::from_milli(e, Some(uid.to_string())))?;
+            if regenerate {
+                let stats = crate::index_mapper::IndexStats::new(&index, &wtxn)
+                    .map_err(|e| Error::from_milli(e, Some(uid.to_string())))?;
+                // Release wtxn as soon as possible because it stops us from registering tasks
+                let mut index_schd_wtxn = self.env.write_txn()?;
+                self.index_mapper.store_stats_of(&mut index_schd_wtxn, uid, &stats)?;
+                index_schd_wtxn.commit()?;
+            }
+            wtxn.commit()?;
         }
 
         Ok(())

crates/meilisearch/tests/upgrade/v1_12/v1_12_0.rs

@@ -206,6 +206,42 @@ async fn check_the_index_scheduler(server: &Server) {
     let (batches, _) = server.batches_filter("afterFinishedAt=2025-01-16T16:47:41Z").await;
     snapshot!(json_string!(batches, { ".results[0].duration" => "[duration]", ".results[0].enqueuedAt" => "[date]", ".results[0].startedAt" => "[date]", ".results[0].finishedAt" => "[date]" }), name: "batches_filter_afterFinishedAt_equal_2025-01-16T16:47:41");
 
+    let (stats, _) = server.stats().await;
+    snapshot!(stats, @r#"
+    {
+      "databaseSize": 425984,
+      "lastUpdate": "2025-01-16T17:18:43.296777845Z",
+      "indexes": {
+        "kefir": {
+          "numberOfDocuments": 1,
+          "isIndexing": false,
+          "fieldDistribution": {
+            "age": 1,
+            "description": 1,
+            "id": 1,
+            "name": 1,
+            "surname": 1
+          }
+        }
+      }
+    }
+    "#);
+    let index = server.index("kefir");
+    let (stats, _) = index.stats().await;
+    snapshot!(stats, @r#"
+    {
+      "numberOfDocuments": 1,
+      "isIndexing": false,
+      "fieldDistribution": {
+        "age": 1,
+        "description": 1,
+        "id": 1,
+        "name": 1,
+        "surname": 1
+      }
+    }
+    "#);
+
     // Delete all the tasks of a specific batch
     let (task, _) = server.delete_tasks("batchUids=10").await;
     server.wait_task(task.uid()).await.succeeded();
@@ -218,15 +254,6 @@ async fn check_the_index_scheduler(server: &Server) {
     let index = server.index("kefirausaurus");
     let (task, _) = index.create(Some("kefid")).await;
     server.wait_task(task.uid()).await.succeeded();
-
-    let (stats, _) = index.stats().await;
-    snapshot!(stats, @r#"
-    {
-      "numberOfDocuments": 0,
-      "isIndexing": false,
-      "fieldDistribution": {}
-    }
-    "#);
 }
 
 /// Ensuring the index roughly works with filter and sort.

crates/milli/src/update/upgrade/mod.rs

@@ -1,17 +1,19 @@
+use heed::RwTxn;
+
 use crate::progress::{Progress, VariableNameStep};
 use crate::{Index, InternalError, Result};
 
-pub fn upgrade(index: &Index, progress: Progress) -> Result<()> {
-    let wtxn = index.env.write_txn()?;
-    let from = index.get_version(&wtxn)?;
+/// Return true if the cached stats of the index must be regenerated
+pub fn upgrade(wtxn: &mut RwTxn, index: &Index, progress: Progress) -> Result<bool> {
+    let from = index.get_version(wtxn)?;
     let upgrade_functions =
         [(v1_12_to_v1_13 as fn(&Index, Progress) -> Result<()>, "Upgrading from v1.12 to v1.13")];
 
-    let start = match from {
+    let (start, regenerate_stats) = match from {
         // If there was no version it means we're coming from the v1.12
-        None | Some((1, 12, _)) => 0,
+        None | Some((1, 12, _)) => (0, false),
         // We must handle the current version in the match because in case of a failure some index may have been upgraded but not other.
-        Some((1, 13, _)) => return Ok(()),
+        Some((1, 13, _)) => return Ok(false),
         Some((major, minor, patch)) => {
             return Err(InternalError::CannotUpgradeToVersion(major, minor, patch).into())
         }
@@ -29,7 +31,7 @@ pub fn upgrade(index: &Index, progress: Progress) -> Result<()> {
         (upgrade_function)(index, progress.clone())?;
     }
 
-    Ok(())
+    Ok(regenerate_stats)
 }
 
 fn v1_12_to_v1_13(_index: &Index, _progress: Progress) -> Result<()> {