Merge #3673

3673: Handle the task queue being full r=irevoire a=dureuill

# Pull Request

## Related issue
Fixes a remaining issue with #3659 where it was not always possible to send tasks back even after deleting some tasks when prompted.

## Tests

- see integration test
- also manually tested with a 1MiB task queue. Was not possible to become unblocked before this PR, is now possible.

## What does this PR do?
- Use the `non_free_pages_size` method to compute the space occupied by the task db instead of the `real_disk_size` which is not always affected by task deletion.
- Expand the test so that it adds a task after the deletion. The test now fails before this PR and succeeds after this PR.

Co-authored-by: Louis Dureuil <louis@meilisearch.com>

index-scheduler/src/lib.rs

@@ -822,7 +822,7 @@ impl IndexScheduler {
 
         // if the task doesn't delete anything and 50% of the task queue is full, we must refuse to enqueue the incomming task
         if !matches!(&kind, KindWithContent::TaskDeletion { tasks, .. } if !tasks.is_empty())
-            && (self.env.real_disk_size()? * 100) / self.env.map_size()? as u64 > 50
+            && (self.env.non_free_pages_size()? * 100) / self.env.map_size()? as u64 > 50
         {
             return Err(Error::NoSpaceLeftInTaskQueue);
         }

meilisearch/tests/tasks/mod.rs

@@ -1050,7 +1050,7 @@ async fn test_task_queue_is_full() {
     "###);
 
     // But we should still be able to register tasks deletion IF they delete something
-    let (result, code) = server.delete_tasks("uids=0").await;
+    let (result, code) = server.delete_tasks("uids=*").await;
     snapshot!(code, @"200 OK");
     snapshot!(json_string!(result, { ".enqueuedAt" => "[date]", ".taskUid" => "uid" }), @r###"
     {
@@ -1062,6 +1062,22 @@ async fn test_task_queue_is_full() {
     }
     "###);
 
+    let result = server.wait_task(result["taskUid"].as_u64().unwrap()).await;
+    snapshot!(json_string!(result["status"]), @r###""succeeded""###);
+
+    // Now we should be able to register tasks again
+    let (result, code) = server.create_index(json!({ "uid": "doggo" })).await;
+    snapshot!(code, @"202 Accepted");
+    snapshot!(json_string!(result, { ".enqueuedAt" => "[date]", ".taskUid" => "uid" }), @r###"
+    {
+      "taskUid": "uid",
+      "indexUid": "doggo",
+      "status": "enqueued",
+      "type": "indexCreation",
+      "enqueuedAt": "[date]"
+    }
+    "###);
+
     // we're going to fill up the queue once again
     loop {
         let (res, code) = server.delete_tasks("uids=0").await;