From 70e378d9fa9be98effbc108b760dbe0b72af994e Mon Sep 17 00:00:00 2001
From: Adrien Guillo <adrien.guillo@gmail.com>
Date: Tue, 2 Jan 2024 17:32:38 +0100
Subject: [PATCH] Skip serializing empty shards

---
 .../file_backed_metastore/file_backed_index/mod.rs    |  4 ++--
 .../file_backed_index/serialize.rs                    | 11 ++++++++++-
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/quickwit/quickwit-metastore/src/metastore/file_backed_metastore/file_backed_index/mod.rs b/quickwit/quickwit-metastore/src/metastore/file_backed_metastore/file_backed_index/mod.rs
index 440765aa21d..6d9d3d817dc 100644
--- a/quickwit/quickwit-metastore/src/metastore/file_backed_metastore/file_backed_index/mod.rs
+++ b/quickwit/quickwit-metastore/src/metastore/file_backed_metastore/file_backed_index/mod.rs
@@ -476,8 +476,8 @@ impl FileBackedIndex {
 
         self.metadata.add_source(source_config)?;
 
-        self.per_source_shards
-            .insert(source_id.clone(), Shards::empty(index_uid, source_id));
+        let shards = Shards::empty(index_uid, source_id.clone());
+        self.per_source_shards.insert(source_id, shards);
         Ok(())
     }
 
diff --git a/quickwit/quickwit-metastore/src/metastore/file_backed_metastore/file_backed_index/serialize.rs b/quickwit/quickwit-metastore/src/metastore/file_backed_metastore/file_backed_index/serialize.rs
index f00847ef9e4..44ada9cba3b 100644
--- a/quickwit/quickwit-metastore/src/metastore/file_backed_metastore/file_backed_index/serialize.rs
+++ b/quickwit/quickwit-metastore/src/metastore/file_backed_metastore/file_backed_index/serialize.rs
@@ -73,7 +73,16 @@ impl From<FileBackedIndex> for FileBackedIndexV0_6 {
         let shards = index
             .per_source_shards
             .into_iter()
-            .map(|(source_id, shards)| (source_id, SerdeShards::from(shards)))
+            .filter_map(|(source_id, shards)| {
+                // Skip serializing empty shards since the feature is hidden and disabled by
+                // default. This way, we can still modify the serialization format without worrying
+                // about backward compatibility post `0.7`.
+                if shards.next_shard_id > 1 {
+                    Some((source_id, SerdeShards::from(shards)))
+                } else {
+                    None
+                }
+            })
             .collect();
         let delete_tasks = index
             .delete_tasks