feat: add LiveReload trait for read-only field indexes (#9295)

* feat: add LiveReload trait for read-only field indexes

* fix: ci

* chore: remove comment

* feat: implement LiveReload for map index (#9296)

lib/segment/src/index/field_index/field_index_base/mod.rs

@@ -10,4 +10,6 @@ pub use builder::{FieldIndexBuilder, FieldIndexBuilderTrait};
 pub use field_index::FieldIndex;
 pub use field_index_read::FieldIndexRead;
 pub use payload_field_index::{PayloadFieldIndex, PayloadFieldIndexRead};
+#[allow(unused_imports)]
+pub(crate) use read_only::LiveReload;
 pub use value_indexer::ValueIndexer;

lib/segment/src/index/field_index/field_index_base/read_only/live_reload.rs

@@ -0,0 +1,41 @@
+use common::counter::hardware_counter::HardwareCounterCell;
+use common::types::PointOffsetType;
+
+use crate::common::operation_error::OperationResult;
+
+/// Common live-reload surface shared by the read-only field-index variants.
+///
+/// A read-only index is opened over a [`UniversalRead`] backend while a writer
+/// keeps appending to the same files. `live_reload` refreshes the in-memory
+/// view to the current on-disk state without a full re-open. Implementers fall
+/// into two shapes:
+///
+/// - immutable mmap variants only re-apply the authoritative `deleted_points`
+///   to their in-memory deletion bitmap — `fs` and `new_points` are unused
+///   because no on-disk state changes after build;
+/// - appendable gridstore variants reload the backing storage through `fs`,
+///   drop `deleted_points` from the in-memory index, then ingest `new_points`
+///   from the refreshed storage view.
+///
+/// `deleted_points` / `new_points` are supplied by the caller (typically the
+/// segment's id-tracker diff accumulated since the previous reload).
+///
+/// [`UniversalRead`]: common::universal_io::UniversalRead
+// No in-crate implementer on the trait-only branch; the per-index impls land
+// on the sibling branches that fork from here.
+#[allow(dead_code)]
+pub(crate) trait LiveReload {
+    /// Filesystem context (`S::Fs` of the backing [`UniversalRead`]) used to
+    /// re-read on-disk state during a reload.
+    ///
+    /// [`UniversalRead`]: common::universal_io::UniversalRead
+    type Fs;
+
+    fn live_reload(
+        &mut self,
+        fs: &Self::Fs,
+        deleted_points: &[PointOffsetType],
+        new_points: &[PointOffsetType],
+        hw_counter: &HardwareCounterCell,
+    ) -> OperationResult<()>;
+}

lib/segment/src/index/field_index/field_index_base/read_only/mod.rs

@@ -1,10 +1,12 @@
 mod lifecycle;
+mod live_reload;
 mod read_ops;
 
 use std::fmt::{Debug, Formatter};
 use std::path::PathBuf;
 
 use common::universal_io::UniversalRead;
+pub(crate) use live_reload::LiveReload;
 
 use crate::common::operation_error::OperationResult;
 use crate::index::field_index::bool_index::ReadOnlyBoolIndex;

lib/segment/src/index/field_index/map_index/mutable_map_index/read_only/live_reload.rs

@@ -6,14 +6,17 @@ use gridstore::Blob;
 use gridstore::error::GridstoreError;
 
 use crate::common::operation_error::OperationResult;
+use crate::index::field_index::LiveReload;
 use crate::index::field_index::map_index::MapIndexKey;
 use crate::index::field_index::map_index::mutable_map_index::read_only::ReadOnlyAppendableMapIndex;
 
-impl<N: MapIndexKey + ?Sized, S: UniversalRead> ReadOnlyAppendableMapIndex<N, S>
+impl<N: MapIndexKey + ?Sized, S: UniversalRead> LiveReload for ReadOnlyAppendableMapIndex<N, S>
 where
     Vec<<N as MapIndexKey>::Owned>: Blob + Send + Sync,
 {
-    pub fn live_reload(
+    type Fs = S::Fs;
+
+    fn live_reload(
         &mut self,
         fs: &S::Fs,
         deleted_points: &[PointOffsetType],

lib/segment/src/index/field_index/map_index/on_disk_map_index/live_reload.rs

@@ -4,15 +4,18 @@ use common::types::PointOffsetType;
 use common::universal_io::UniversalRead;
 
 use crate::common::operation_error::OperationResult;
+use crate::index::field_index::LiveReload;
 use crate::index::field_index::map_index::MapIndexKey;
 use crate::index::field_index::map_index::on_disk_map_index::OnDiskMapIndex;
 
-impl<N, S> OnDiskMapIndex<N, S>
+impl<N, S> LiveReload for OnDiskMapIndex<N, S>
 where
     N: MapIndexKey + Key + ?Sized,
     S: UniversalRead,
 {
-    pub fn live_reload(
+    type Fs = S::Fs;
+
+    fn live_reload(
         &mut self,
         _fs: &S::Fs,
         deleted_points: &[PointOffsetType],