diff --git a/Cargo.lock b/Cargo.lock
index 1be1e90c9c1927..bc8eb6c1bd6ee7 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -5478,7 +5478,7 @@ dependencies = [
  "dir-diff",
  "flate2",
  "fnv",
- "itertools 0.9.0",
+ "itertools 0.10.1",
  "lazy_static",
  "libc",
  "libloading 0.6.2",
diff --git a/core/src/broadcast_stage/broadcast_duplicates_run.rs b/core/src/broadcast_stage/broadcast_duplicates_run.rs
index e73bd36299760c..195fcc0deeecf0 100644
--- a/core/src/broadcast_stage/broadcast_duplicates_run.rs
+++ b/core/src/broadcast_stage/broadcast_duplicates_run.rs
@@ -216,8 +216,9 @@ impl BroadcastRun for BroadcastDuplicatesRun {
         let mut stakes: Vec<(Pubkey, u64)> = bank
             .epoch_staked_nodes(bank_epoch)
             .unwrap()
-            .into_iter()
-            .filter(|(pubkey, _)| *pubkey != self.keypair.pubkey())
+            .iter()
+            .filter(|(pubkey, _)| **pubkey != self.keypair.pubkey())
+            .map(|(pubkey, stake)| (*pubkey, *stake))
             .collect();
         stakes.sort_by(|(l_key, l_stake), (r_key, r_stake)| {
             if r_stake == l_stake {
diff --git a/gossip/src/cluster_info.rs b/gossip/src/cluster_info.rs
index 2a92aa5587170d..0afe8cdac59959 100644
--- a/gossip/src/cluster_info.rs
+++ b/gossip/src/cluster_info.rs
@@ -1749,7 +1749,7 @@ impl ClusterInfo {
                                 Some(root_bank.feature_set.clone()),
                             )
                         }
-                        None => (HashMap::new(), None),
+                        None => (Arc::default(), None),
                     };
                     let require_stake_for_gossip =
                         self.require_stake_for_gossip(feature_set.as_deref(), &stakes);
@@ -2542,7 +2542,7 @@ impl ClusterInfo {
         // feature does not roll back (if the feature happens to get enabled in
         // a minority fork).
         let (feature_set, stakes) = match bank_forks {
-            None => (None, HashMap::default()),
+            None => (None, Arc::default()),
             Some(bank_forks) => {
                 let bank = bank_forks.read().unwrap().root_bank();
                 let feature_set = bank.feature_set.clone();
diff --git a/ledger/src/leader_schedule_utils.rs b/ledger/src/leader_schedule_utils.rs
index 0217b11cd36195..dd3f652167b2b6 100644
--- a/ledger/src/leader_schedule_utils.rs
+++ b/ledger/src/leader_schedule_utils.rs
@@ -13,7 +13,10 @@ pub fn leader_schedule(epoch: Epoch, bank: &Bank) -> Option<LeaderSchedule> {
     bank.epoch_staked_nodes(epoch).map(|stakes| {
         let mut seed = [0u8; 32];
         seed[0..8].copy_from_slice(&epoch.to_le_bytes());
-        let mut stakes: Vec<_> = stakes.into_iter().collect();
+        let mut stakes: Vec<_> = stakes
+            .iter()
+            .map(|(pubkey, stake)| (*pubkey, *stake))
+            .collect();
         sort_stakes(&mut stakes);
         LeaderSchedule::new(
             &stakes,
@@ -91,7 +94,11 @@ mod tests {
                 .genesis_config;
         let bank = Bank::new(&genesis_config);
 
-        let pubkeys_and_stakes: Vec<_> = bank.staked_nodes().into_iter().collect();
+        let pubkeys_and_stakes: Vec<_> = bank
+            .staked_nodes()
+            .iter()
+            .map(|(pubkey, stake)| (*pubkey, *stake))
+            .collect();
         let seed = [0u8; 32];
         let leader_schedule = LeaderSchedule::new(
             &pubkeys_and_stakes,
diff --git a/programs/bpf/Cargo.lock b/programs/bpf/Cargo.lock
index ab78d1adca794e..face9f93c70d4a 100644
--- a/programs/bpf/Cargo.lock
+++ b/programs/bpf/Cargo.lock
@@ -1430,9 +1430,9 @@ dependencies = [
 
 [[package]]
 name = "itertools"
-version = "0.10.0"
+version = "0.10.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "37d572918e350e82412fe766d24b15e6682fb2ed2bbe018280caa810397cb319"
+checksum = "a9a9d19fa1e79b6215ff29b9d6880b706147f16e9b1dbb1e4e5947b5b02bc5e3"
 dependencies = [
  "either",
 ]
@@ -2764,7 +2764,7 @@ dependencies = [
  "bincode",
  "byteorder 1.3.4",
  "elf",
- "itertools 0.10.0",
+ "itertools 0.10.3",
  "log",
  "miow 0.2.2",
  "net2",
@@ -3501,7 +3501,7 @@ dependencies = [
  "dir-diff",
  "flate2",
  "fnv",
- "itertools 0.9.0",
+ "itertools 0.10.3",
  "lazy_static",
  "libc",
  "libloading",
diff --git a/runtime/Cargo.toml b/runtime/Cargo.toml
index aecc7238665391..e6180279e41e53 100644
--- a/runtime/Cargo.toml
+++ b/runtime/Cargo.toml
@@ -21,7 +21,7 @@ crossbeam-channel = "0.4"
 dir-diff = "0.3.2"
 flate2 = "1.0.14"
 fnv = "1.0.7"
-itertools = "0.9.0"
+itertools = "0.10.1"
 lazy_static = "1.4.0"
 libc = "0.2.81"
 libloading = "0.6.2"
diff --git a/runtime/src/bank.rs b/runtime/src/bank.rs
index f951d29403c020..e2a23ed9fcbfca 100644
--- a/runtime/src/bank.rs
+++ b/runtime/src/bank.rs
@@ -5282,7 +5282,7 @@ impl Bank {
         self.stakes_cache.stakes().stake_delegations().clone()
     }
 
-    pub fn staked_nodes(&self) -> HashMap<Pubkey, u64> {
+    pub fn staked_nodes(&self) -> Arc<HashMap<Pubkey, u64>> {
         self.stakes_cache.stakes().staked_nodes()
     }
 
@@ -5312,7 +5312,7 @@ impl Bank {
         &self.epoch_stakes
     }
 
-    pub fn epoch_staked_nodes(&self, epoch: Epoch) -> Option<HashMap<Pubkey, u64>> {
+    pub fn epoch_staked_nodes(&self, epoch: Epoch) -> Option<Arc<HashMap<Pubkey, u64>>> {
         Some(self.epoch_stakes.get(&epoch)?.stakes().staked_nodes())
     }
 
diff --git a/runtime/src/stakes.rs b/runtime/src/stakes.rs
index 9a7e0d7bbc7b8b..bf0758267c8f1b 100644
--- a/runtime/src/stakes.rs
+++ b/runtime/src/stakes.rs
@@ -335,7 +335,7 @@ impl Stakes {
         &self.stake_delegations
     }
 
-    pub fn staked_nodes(&self) -> HashMap<Pubkey, u64> {
+    pub fn staked_nodes(&self) -> Arc<HashMap<Pubkey, u64>> {
         self.vote_accounts.staked_nodes()
     }
 
diff --git a/runtime/src/vote_account.rs b/runtime/src/vote_account.rs
index 808b555212e435..4bae3bbe0a7885 100644
--- a/runtime/src/vote_account.rs
+++ b/runtime/src/vote_account.rs
@@ -1,4 +1,5 @@
 use {
+    itertools::Itertools,
     serde::{
         de::{Deserialize, Deserializer},
         ser::{Serialize, Serializer},
@@ -40,9 +41,11 @@ pub struct VoteAccounts {
     // Inner Arc is meant to implement copy-on-write semantics as opposed to
     // sharing mutations (hence RwLock<Arc<...>> instead of Arc<RwLock<...>>).
     staked_nodes: RwLock<
-        HashMap<
-            Pubkey, // VoteAccount.vote_state.node_pubkey.
-            u64,    // Total stake across all vote-accounts.
+        Arc<
+            HashMap<
+                Pubkey, // VoteAccount.vote_state.node_pubkey.
+                u64,    // Total stake across all vote-accounts.
+            >,
         >,
     >,
     staked_nodes_once: Once,
@@ -69,20 +72,19 @@ impl VoteAccount {
 }
 
 impl VoteAccounts {
-    pub fn staked_nodes(&self) -> HashMap<Pubkey, u64> {
+    pub fn staked_nodes(&self) -> Arc<HashMap<Pubkey, u64>> {
         self.staked_nodes_once.call_once(|| {
-            let mut staked_nodes = HashMap::new();
-            for (stake, vote_account) in
-                self.vote_accounts.values().filter(|(stake, _)| *stake != 0)
-            {
-                if let Some(node_pubkey) = vote_account.node_pubkey() {
-                    staked_nodes
-                        .entry(node_pubkey)
-                        .and_modify(|s| *s += *stake)
-                        .or_insert(*stake);
-                }
-            }
-            *self.staked_nodes.write().unwrap() = staked_nodes
+            let staked_nodes = self
+                .vote_accounts
+                .values()
+                .filter(|(stake, _)| *stake != 0)
+                .filter_map(|(stake, vote_account)| {
+                    let node_pubkey = vote_account.node_pubkey()?;
+                    Some((node_pubkey, stake))
+                })
+                .into_grouping_map()
+                .aggregate(|acc, _node_pubkey, stake| Some(acc.unwrap_or_default() + stake));
+            *self.staked_nodes.write().unwrap() = Arc::new(staked_nodes)
         });
         self.staked_nodes.read().unwrap().clone()
     }
@@ -135,9 +137,9 @@ impl VoteAccounts {
     fn add_node_stake(&mut self, stake: u64, vote_account: &VoteAccount) {
         if stake != 0 && self.staked_nodes_once.is_completed() {
             if let Some(node_pubkey) = vote_account.node_pubkey() {
-                self.staked_nodes
-                    .write()
-                    .unwrap()
+                let mut staked_nodes = self.staked_nodes.write().unwrap();
+                let staked_nodes = Arc::make_mut(&mut staked_nodes);
+                staked_nodes
                     .entry(node_pubkey)
                     .and_modify(|s| *s += stake)
                     .or_insert(stake);
@@ -148,7 +150,9 @@ impl VoteAccounts {
     fn sub_node_stake(&mut self, stake: u64, vote_account: &VoteAccount) {
         if stake != 0 && self.staked_nodes_once.is_completed() {
             if let Some(node_pubkey) = vote_account.node_pubkey() {
-                match self.staked_nodes.write().unwrap().entry(node_pubkey) {
+                let mut staked_nodes = self.staked_nodes.write().unwrap();
+                let staked_nodes = Arc::make_mut(&mut staked_nodes);
+                match staked_nodes.entry(node_pubkey) {
                     Entry::Vacant(_) => panic!("this should not happen!"),
                     Entry::Occupied(mut entry) => match entry.get().cmp(&stake) {
                         Ordering::Less => panic!("subtraction value exceeds node's stake"),
@@ -485,7 +489,7 @@ mod tests {
             if (k + 1) % 128 == 0 {
                 assert_eq!(
                     staked_nodes(&accounts[..k + 1]),
-                    vote_accounts.staked_nodes()
+                    *vote_accounts.staked_nodes()
                 );
             }
         }
@@ -495,7 +499,7 @@ mod tests {
             let (pubkey, (_, _)) = accounts.swap_remove(index);
             vote_accounts.remove(&pubkey);
             if (k + 1) % 32 == 0 {
-                assert_eq!(staked_nodes(&accounts), vote_accounts.staked_nodes());
+                assert_eq!(staked_nodes(&accounts), *vote_accounts.staked_nodes());
             }
         }
         // Modify the stakes for some of the accounts.
@@ -510,7 +514,7 @@ mod tests {
             }
             *stake = new_stake;
             if (k + 1) % 128 == 0 {
-                assert_eq!(staked_nodes(&accounts), vote_accounts.staked_nodes());
+                assert_eq!(staked_nodes(&accounts), *vote_accounts.staked_nodes());
             }
         }
         // Remove everything.
@@ -519,7 +523,7 @@ mod tests {
             let (pubkey, (_, _)) = accounts.swap_remove(index);
             vote_accounts.remove(&pubkey);
             if accounts.len() % 32 == 0 {
-                assert_eq!(staked_nodes(&accounts), vote_accounts.staked_nodes());
+                assert_eq!(staked_nodes(&accounts), *vote_accounts.staked_nodes());
             }
         }
         assert!(vote_accounts.staked_nodes.read().unwrap().is_empty());