chore: add docs

Signed-off-by: Zhenchi <[email protected]>

src/mito2/src/sst/index.rs

@@ -12,5 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+#![allow(dead_code)]
+
 pub mod applier;
 mod codec;

src/mito2/src/sst/index/applier.rs

@@ -19,15 +19,22 @@ use std::sync::Arc;
 use index::inverted_index::search::index_apply::IndexApplier;
 use object_store::ObjectStore;
 
-#[allow(dead_code)]
-#[derive(Clone)]
+/// The [`SstIndexApplier`] is responsible for applying predicates to the provided SST files
+/// and returning the relevant row group ids for further scan.
 pub struct SstIndexApplier {
+    /// The root directory of the region.
     region_dir: String,
+
+    /// Object store responsible for accessing SST files.
     object_store: ObjectStore,
+
+    /// Predifined index applier used to apply predicates to index files
+    /// and return the relevant row group ids for further scan.
     index_applier: Arc<dyn IndexApplier>,
 }
 
 impl SstIndexApplier {
+    /// Creates a new [`SstIndexApplier`].
     pub fn new(
         region_dir: String,
         object_store: ObjectStore,

src/mito2/src/sst/index/applier/builder.rs

@@ -60,7 +60,6 @@ pub struct SstIndexApplierBuilder<'a> {
 
 impl<'a> SstIndexApplierBuilder<'a> {
     /// Creates a new [`SstIndexApplierBuilder`].
-    #[allow(dead_code)]
     pub fn new(
         region_dir: String,
         object_store: ObjectStore,
@@ -76,7 +75,6 @@ impl<'a> SstIndexApplierBuilder<'a> {
 
     /// Consumes the builder to construct an [`SstIndexApplier`], optionally returned based on
     /// the expressions provided. If no predicates match, returns `None`.
-    #[allow(dead_code)]
     pub fn build(mut self, exprs: &[Expr]) -> Result<Option<SstIndexApplier>> {
         for expr in exprs {
             self.traverse_and_collect(expr.df_expr())?;