add metric for ancient can't move slots

accounts-db/src/accounts_db.rs

@@ -2014,10 +2014,10 @@ pub(crate) struct ShrinkStatsSub {
     pub(crate) store_accounts_timing: StoreAccountsTiming,
     pub(crate) rewrite_elapsed_us: u64,
     pub(crate) create_and_insert_store_elapsed_us: u64,
+    pub(crate) number_unpackable_slots: usize,
 }
 
 impl ShrinkStatsSub {
-    #[allow(dead_code)]
     pub(crate) fn accumulate(&mut self, other: &Self) {
         self.store_accounts_timing
             .accumulate(&other.store_accounts_timing);
@@ -2026,6 +2026,7 @@ impl ShrinkStatsSub {
             self.create_and_insert_store_elapsed_us,
             other.create_and_insert_store_elapsed_us
         );
+        saturating_add_assign!(self.number_unpackable_slots, other.number_unpackable_slots);
     }
 }
 
@@ -2041,6 +2042,7 @@ pub struct ShrinkStats {
     handle_reclaims_elapsed: AtomicU64,
     remove_old_stores_shrink_us: AtomicU64,
     rewrite_elapsed: AtomicU64,
+    number_unpackable_slots: AtomicU64,
     drop_storage_entries_elapsed: AtomicU64,
     recycle_stores_write_elapsed: AtomicU64,
     accounts_removed: AtomicUsize,
@@ -2219,6 +2221,13 @@ impl ShrinkAncientStats {
                     self.shrink_stats.rewrite_elapsed.swap(0, Ordering::Relaxed) as i64,
                     i64
                 ),
+                (
+                    "number_unpackable_slots",
+                    self.shrink_stats
+                        .number_unpackable_slots
+                        .swap(0, Ordering::Relaxed) as i64,
+                    i64
+                ),
                 (
                     "drop_storage_entries_elapsed",
                     self.shrink_stats
@@ -4177,6 +4186,9 @@ impl AccountsDb {
         shrink_stats
             .rewrite_elapsed
             .fetch_add(stats_sub.rewrite_elapsed_us, Ordering::Relaxed);
+        shrink_stats
+            .number_unpackable_slots
+            .fetch_add(stats_sub.number_unpackable_slots as u64, Ordering::Relaxed);
     }
 
     /// get stores for 'slot'

accounts-db/src/ancient_append_vecs.rs

@@ -299,6 +299,7 @@ impl AccountsDb {
             );
 
         let accounts_to_combine = self.calc_accounts_to_combine(&accounts_per_storage);
+        metrics.number_unpackable_slots += accounts_to_combine.number_unpackable_slots;
 
         // pack the accounts with 1 ref
         let pack = PackedAncientStorage::pack(
@@ -385,6 +386,7 @@ impl AccountsDb {
             store_accounts_timing,
             rewrite_elapsed_us,
             create_and_insert_store_elapsed_us,
+            number_unpackable_slots: 0,
         });
         write_ancient_accounts
             .shrinks_in_progress
@@ -584,13 +586,15 @@ impl AccountsDb {
                 target_slots_sorted.push(info.slot);
             }
         }
+        let number_unpackable_slots = remove.len();
         remove.into_iter().rev().for_each(|i| {
             accounts_to_combine.remove(i);
         });
         AccountsToCombine {
             accounts_to_combine,
             accounts_keep_slots,
             target_slots_sorted,
+            number_unpackable_slots,
         }
     }
 
@@ -718,6 +722,8 @@ struct AccountsToCombine<'a> {
     /// Some of these slots will have ancient append vecs created at them to contain everything in 'accounts_to_combine'
     /// The rest will become dead slots with no accounts in them.
     target_slots_sorted: Vec<Slot>,
+    /// when scanning, this many slots contained accounts that could not be packed because accounts with ref_count > 1 existed.
+    number_unpackable_slots: usize,
 }
 
 #[derive(Default)]
@@ -3135,6 +3141,7 @@ pub mod tests {
                 accounts_keep_slots: HashMap::default(),
                 accounts_to_combine: vec![shrink_collect],
                 target_slots_sorted: Vec::default(),
+                number_unpackable_slots: 0,
             };
             db.addref_accounts_failed_to_shrink_ancient(accounts_to_combine);
             db.accounts_index.scan(