It is only having an Arc<DB> for cheap cloning

src/cache/delta_reader.rs

@@ -16,20 +16,20 @@ pub type SnapshotIterRange<'a> = btree_map::Range<'a, SchemaKey, Operation>;
 /// Read-only data provider that supports a list of snapshots on top of [`DB`].
 /// Maintains total ordering and respects uncommited deletions.
 /// Should not write to underlying [`DB`].
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub struct DeltaReader {
  /// Set of not commited changes in chronological order.
  /// Meaning that the first snapshot in the vector is the oldest and the latest is the most recent.
  /// If keys are equal, the value from more recent snapshot is taken.
  snapshots: Vec<Arc<SchemaBatch>>,
  /// Reading finalized data from here.
- db: DB,
+ db: Arc<DB>,
 }
 
 impl DeltaReader {
  /// Creates new [`DeltaReader`] with given [`DB`] and vector with uncommited snapshots of [`SchemaBatch`].
  /// Snapshots should be in chronological order.
- pub fn new(db: DB, snapshots: Vec<Arc<SchemaBatch>>) -> Self {
+ pub fn new(db: Arc<DB>, snapshots: Vec<Arc<SchemaBatch>>) -> Self {
  Self { snapshots, db }
  }
 
@@ -381,12 +381,12 @@ mod tests {
  const FIELD_6: TestCompositeField = TestCompositeField(4, 2, 1);
  const FIELD_7: TestCompositeField = TestCompositeField(4, 3, 0);
 
- fn open_db(dir: impl AsRef<Path>) -> DB {
+ fn open_db(dir: impl AsRef<Path>) -> Arc<DB> {
  let column_families = vec![DEFAULT_COLUMN_FAMILY_NAME, TestSchema::COLUMN_FAMILY_NAME];
  let mut db_opts = rocksdb::Options::default();
  db_opts.create_if_missing(true);
  db_opts.create_missing_column_families(true);
- DB::open(dir, "test", column_families, &db_opts).expect("Failed to open DB.")
+ Arc::new(DB::open(dir, "test", column_families, &db_opts).expect("Failed to open DB."))
  }
 
  // Test utils
@@ -893,7 +893,7 @@ mod tests {
  "iter_rev should be sorted in reversed order"
  );
 
- // Building a reference for all K/V for validation if basic check is passed.
+ // Building a reference for all K/V for validation if the basic check is passed.
  let mut all_kv: BTreeMap<TestCompositeField, TestField> = BTreeMap::new();
  for (key, value) in db_entries {
  all_kv.insert(key, value);