Add candidates by sorted keys, decreasing number of lock acquires

This is a minor optimization of how new cleaning candidates are
created in the candidates list.  The candidate bin lock is acquired
only once for each bin because the pubkeys are sorted by bins, and
previously unlocked bin is reused until pubkeys from a new bin start
being added to the candidates list.

accounts-db/src/accounts_db.rs

@@ -3079,11 +3079,34 @@ impl AccountsDb {
     ) {
         let uncleaned_slots = self.collect_uncleaned_slots_up_to_slot(max_slot_inclusive);
         for uncleaned_slot in uncleaned_slots.into_iter() {
-            if let Some((_removed_slot, removed_pubkeys)) =
+            if let Some((_removed_slot, mut removed_pubkeys)) =
                 self.uncleaned_pubkeys.remove(&uncleaned_slot)
             {
-                for removed_pubkey in removed_pubkeys {
-                    self.insert_pubkey(candidates, removed_pubkey);
+                // Sort all keys by bin index so that we can insert
+                // them in `candidates` more efficiently.
+                removed_pubkeys.sort_by(|a, b| {
+                    self.accounts_index
+                        .bin_calculator
+                        .bin_from_pubkey(a)
+                        .cmp(&self.accounts_index.bin_calculator.bin_from_pubkey(b))
+                });
+                if let Some(first_removed_pubkey) = removed_pubkeys.first() {
+                    let mut prev_bin = self
+                        .accounts_index
+                        .bin_calculator
+                        .bin_from_pubkey(first_removed_pubkey);
+                    let mut candidates_bin = candidates[prev_bin].write().unwrap();
+                    for removed_pubkey in removed_pubkeys {
+                        let curr_bin = self
+                            .accounts_index
+                            .bin_calculator
+                            .bin_from_pubkey(&removed_pubkey);
+                        if curr_bin != prev_bin {
+                            candidates_bin = candidates[curr_bin].write().unwrap();
+                            prev_bin = curr_bin;
+                        }
+                        candidates_bin.insert(removed_pubkey, CleaningInfo::default());
+                    }
                 }
             }
         }