Clarify comment and remove anchor_slot garbage

beacon_node/store/src/hdiff.rs

@@ -340,8 +340,12 @@ impl HierarchyModuli {
 
     /// Return `true` if the database ops for this slot should be committed immediately.
     ///
-    /// This is the case for all diffs in the 2nd lowest layer and above, which are required by diffs
-    /// in the 1st layer.
+    /// This is the case for all diffs aside from the ones in the leaf layer. To store a diff
+    /// might require loading the state at the previous layer, in which case the diff for that
+    /// layer must already have been stored.
+    ///
+    /// In future we may be able to handle this differently (with proper transaction semantics
+    /// rather than LevelDB's "write batches").
     pub fn should_commit_immediately(&self, slot: Slot) -> Result<bool, Error> {
         // If there's only 1 layer of snapshots, then commit only when writing a snapshot.
         self.moduli.get(1).map_or_else(

beacon_node/store/src/hot_cold_store.rs

@@ -2914,7 +2914,6 @@ pub fn migrate_database<E: EthSpec, Hot: ItemStore<E>, Cold: ItemStore<E>>(
     // boundary (in order for the hot state summary scheme to work).
     let current_split_slot = store.split.read_recursive().slot;
     let anchor_info = store.anchor_info.read_recursive().clone();
-    let anchor_slot = anchor_info.as_ref().map(|a| a.anchor_slot);
 
     if finalized_state.slot() < current_split_slot {
         return Err(HotColdDBError::FreezeSlotError {
@@ -2938,10 +2937,7 @@ pub fn migrate_database<E: EthSpec, Hot: ItemStore<E>, Cold: ItemStore<E>>(
     // Iterate in descending order until the current split slot
     let state_roots = RootsIterator::new(&store, finalized_state)
         .take_while(|result| match result {
-            Ok((_, _, slot)) => {
-                slot >= &current_split_slot
-                    && anchor_slot.map_or(true, |anchor_slot| slot >= &anchor_slot)
-            }
+            Ok((_, _, slot)) => *slot >= current_split_slot,
             Err(_) => true,
         })
         .collect::<Result<Vec<_>, _>>()?;