refactor shrink candidate result struct

accounts-db/src/accounts_db.rs

@@ -2442,6 +2442,11 @@ pub struct PubkeyHashAccount {
     pub account: AccountSharedData,
 }
 
+struct SelectShrinkCandidateResult {
+    pub to_shrink: HashMap<Slot, Arc<AccountStorageEntry>>,
+    pub next_batch: ShrinkCandidates,
+}
+
 impl AccountsDb {
     pub const DEFAULT_ACCOUNTS_HASH_CACHE_DIR: &'static str = "accounts_hash_cache";
 
@@ -4287,19 +4292,17 @@ impl AccountsDb {
         self.storage.all_slots()
     }
 
-    /// Given the input `ShrinkCandidates`, this function sorts the stores by their alive ratio
-    /// in increasing order with the most sparse entries in the front. It will then simulate the
-    /// shrinking by working on the most sparse entries first and if the overall alive ratio is
-    /// achieved, it will stop and return:
-    /// first tuple element: the filtered-down candidates and
-    /// second duple element: the candidates which
-    /// are skipped in this round and might be eligible for the future shrink.
+    /// Given the input `ShrinkCandidates`, this function selects the stores by their shrinking byte-savings
+    /// in decreasing order to raise overall alive ratio to achieve the desired `shrink_ratio`.
+    /// Returns SelectShrinkCandidateResult:
+    ///     - the candidates to shrink in this pass
+    ///     - the remaining candidates to retry in next pass
     fn select_candidates_by_total_usage(
         &self,
         shrink_slots: &ShrinkCandidates,
         shrink_ratio: f64,
         oldest_non_ancient_slot: Option<Slot>,
-    ) -> (HashMap<Slot, Arc<AccountStorageEntry>>, ShrinkCandidates) {
+    ) -> SelectShrinkCandidateResult {
         struct StoreUsageInfo {
             slot: Slot,
             alive_ratio: f64,
@@ -4385,7 +4388,10 @@ impl AccountsDb {
             .map(|s| s.slot)
             .collect();
 
-        (shrink_slots, shrink_slots_next_batch)
+        SelectShrinkCandidateResult {
+            to_shrink: shrink_slots,
+            next_batch: shrink_slots_next_batch,
+        }
     }
 
     fn get_roots_less_than(&self, slot: Slot) -> Vec<Slot> {
@@ -4778,13 +4784,15 @@ impl AccountsDb {
 
         let (shrink_slots, shrink_slots_next_batch) = {
             if let AccountShrinkThreshold::TotalSpace { shrink_ratio } = self.shrink_ratio {
-                let (shrink_slots, shrink_slots_next_batch) = self
-                    .select_candidates_by_total_usage(
-                        &shrink_candidates_slots,
-                        shrink_ratio,
-                        self.ancient_append_vec_offset
-                            .map(|_| oldest_non_ancient_slot),
-                    );
+                let SelectShrinkCandidateResult {
+                    to_shrink: shrink_slots,
+                    next_batch: shrink_slots_next_batch,
+                } = self.select_candidates_by_total_usage(
+                    &shrink_candidates_slots,
+                    shrink_ratio,
+                    self.ancient_append_vec_offset
+                        .map(|_| oldest_non_ancient_slot),
+                );
                 (shrink_slots, Some(shrink_slots_next_batch))
             } else {
                 (
@@ -13382,8 +13390,10 @@ pub mod tests {
         let candidates = ShrinkCandidates::default();
         let db = AccountsDb::new_single_for_tests();
 
-        let (selected_candidates, next_candidates) =
-            db.select_candidates_by_total_usage(&candidates, DEFAULT_ACCOUNTS_SHRINK_RATIO, None);
+        let SelectShrinkCandidateResult {
+            to_shrink: selected_candidates,
+            next_batch: next_candidates,
+        } = db.select_candidates_by_total_usage(&candidates, DEFAULT_ACCOUNTS_SHRINK_RATIO, None);
 
         assert_eq!(0, selected_candidates.len());
         assert_eq!(0, next_candidates.len());
@@ -13454,8 +13464,10 @@ pub mod tests {
         // The target ratio is also set to larger than store2's alive ratio: 0.5 so that it would be added
         // to the candidates list for next round.
         let target_alive_ratio = 0.6;
-        let (selected_candidates, next_candidates) =
-            db.select_candidates_by_total_usage(&candidates, target_alive_ratio, None);
+        let SelectShrinkCandidateResult {
+            to_shrink: selected_candidates,
+            next_batch: next_candidates,
+        } = db.select_candidates_by_total_usage(&candidates, target_alive_ratio, None);
         assert_eq!(1, selected_candidates.len());
         assert!(selected_candidates.contains(&slot_id_1));
         assert_eq!(1, next_candidates.len());
@@ -13520,8 +13532,10 @@ pub mod tests {
 
         // Set the target ratio to default (0.8), both store1 and store2 must be selected and store3 is ignored.
         let target_alive_ratio = DEFAULT_ACCOUNTS_SHRINK_RATIO;
-        let (selected_candidates, next_candidates) =
-            db.select_candidates_by_total_usage(&candidates, target_alive_ratio, None);
+        let SelectShrinkCandidateResult {
+            to_shrink: selected_candidates,
+            next_batch: next_candidates,
+        } = db.select_candidates_by_total_usage(&candidates, target_alive_ratio, None);
         assert_eq!(2, selected_candidates.len());
         assert!(selected_candidates.contains(&slot_id_1));
         assert!(selected_candidates.contains(&slot_id_2));
@@ -13577,7 +13591,10 @@ pub mod tests {
         for newest_ancient_slot in [None, Some(slot1), Some(slot2)] {
             // Set the target ratio to default (0.8), both stores from the two different slots must be selected.
             let target_alive_ratio = DEFAULT_ACCOUNTS_SHRINK_RATIO;
-            let (selected_candidates, next_candidates) = db.select_candidates_by_total_usage(
+            let SelectShrinkCandidateResult {
+                to_shrink: selected_candidates,
+                next_batch: next_candidates,
+            } = db.select_candidates_by_total_usage(
                 &candidates,
                 target_alive_ratio,
                 newest_ancient_slot.map(|newest_ancient_slot| newest_ancient_slot + 1),