[MetadataServer] minor changes

- Always flush metadata-server CFs on shutdown
- INFO logging for leadership changes events

```
// intentionally left empty
```

crates/metadata-server/src/raft/server.rs

@@ -656,8 +656,11 @@ impl Member {
         self.is_leader = self.raw_node.raft.leader_id == self.raw_node.raft.id;
 
         if previous_is_leader && !self.is_leader {
-            debug!("Lost metadata store leadership");
             let known_leader = self.known_leader();
+            info!(
+                possible_leader = ?known_leader,
+                "Lost metadata store leadership"
+            );
 
             // todo we might fail some of the request too eagerly here because the answer might be
             //  stored in the unapplied log entries. Better to fail the callbacks based on
@@ -670,7 +673,7 @@ impl Member {
             self.fail_join_callbacks(|| JoinClusterError::NotLeader(known_leader.clone()));
             self.read_index_to_request_id.clear();
         } else if !previous_is_leader && self.is_leader {
-            debug!("Won metadata store leadership");
+            info!("Won metadata store leadership");
         }
     }
 

crates/metadata-server/src/raft/storage.rs

@@ -8,14 +8,21 @@
 // the Business Source License, use of this software will be governed
 // by the Apache License, Version 2.0.
 
-use crate::raft::RaftConfiguration;
-use crate::{util, StorageId};
+use std::array::TryFromSliceError;
+use std::cell::RefCell;
+use std::mem::size_of;
+use std::sync::Arc;
+use std::{error, mem};
+
 use bytes::{BufMut, BytesMut};
 use flexbuffers::{DeserializationError, SerializationError};
 use protobuf::{Message, ProtobufError};
 use raft::eraftpb::{ConfState, Entry, Snapshot};
 use raft::prelude::HardState;
 use raft::{GetEntriesContext, RaftState, Storage, StorageError};
+use rocksdb::{BoundColumnFamily, DBPinnableSlice, ReadOptions, WriteBatch, WriteOptions, DB};
+use tracing::debug;
+
 use restate_rocksdb::{
     CfName, CfPrefixPattern, DbName, DbSpecBuilder, IoMode, Priority, RocksDb, RocksDbManager,
     RocksError,
@@ -24,13 +31,9 @@ use restate_types::config::{data_dir, MetadataServerOptions, RocksDbOptions};
 use restate_types::errors::GenericError;
 use restate_types::live::BoxedLiveLoad;
 use restate_types::nodes_config::NodesConfiguration;
-use rocksdb::{BoundColumnFamily, DBPinnableSlice, ReadOptions, WriteBatch, WriteOptions, DB};
-use std::array::TryFromSliceError;
-use std::cell::RefCell;
-use std::mem::size_of;
-use std::sync::Arc;
-use std::{error, mem};
-use tracing::debug;
+
+use crate::raft::RaftConfiguration;
+use crate::{util, StorageId};
 
 const DB_NAME: &str = "raft-metadata-store";
 const RAFT_CF: &str = "raft";
@@ -117,6 +120,7 @@ impl RocksDbStorage {
             util::cf_options(options.rocksdb_memory_budget()),
         )
         .ensure_column_families(cfs)
+        .add_to_flush_on_shutdown(CfPrefixPattern::ANY)
         .build()
         .expect("valid spec");