bank: Prune older epoch stakes

ci/test-stable.sh

@@ -111,7 +111,7 @@ test-move)
   ;;
 test-local-cluster)
   _ cargo +"$rust_stable" build --release --bins ${V:+--verbose}
-  _ cargo +"$rust_stable" test --release --package solana-local-cluster ${V:+--verbose} -- --nocapture
+  _ cargo +"$rust_stable" test --release --package solana-local-cluster ${V:+--verbose} -- --nocapture --test-threads=1
   exit 0
   ;;
 *)

local-cluster/src/local_cluster.rs

@@ -733,6 +733,7 @@ mod test {
             cluster_lamports: 100,
             ticks_per_slot: 8,
             slots_per_epoch: MINIMUM_SLOTS_PER_EPOCH as u64,
+            stakers_slot_offset: MINIMUM_SLOTS_PER_EPOCH as u64,
             ..ClusterConfig::default()
         };
         let cluster = LocalCluster::new(&config);

local-cluster/tests/local_cluster.rs

@@ -449,6 +449,7 @@ fn test_two_unbalanced_stakes() {
         validator_configs: vec![validator_config.clone(); 2],
         ticks_per_slot: num_ticks_per_slot,
         slots_per_epoch: num_slots_per_epoch,
+        stakers_slot_offset: num_slots_per_epoch,
         poh_config: PohConfig::new_sleep(Duration::from_millis(1000 / num_ticks_per_second)),
         ..ClusterConfig::default()
     });
@@ -497,15 +498,16 @@ fn test_forwarding() {
 fn test_restart_node() {
     solana_logger::setup();
     error!("test_restart_node");
-    let slots_per_epoch = MINIMUM_SLOTS_PER_EPOCH as u64;
+    let slots_per_epoch = MINIMUM_SLOTS_PER_EPOCH * 2 as u64;
     let ticks_per_slot = 16;
     let validator_config = ValidatorConfig::default();
     let mut cluster = LocalCluster::new(&ClusterConfig {
-        node_stakes: vec![3],
+        node_stakes: vec![100; 1],
         cluster_lamports: 100,
         validator_configs: vec![validator_config.clone()],
         ticks_per_slot,
         slots_per_epoch,
+        stakers_slot_offset: slots_per_epoch,
         ..ClusterConfig::default()
     });
     let nodes = cluster.get_node_pubkeys();

runtime/src/bank.rs

@@ -60,6 +60,8 @@ use std::{
 
 pub const SECONDS_PER_YEAR: f64 = (365.25 * 24.0 * 60.0 * 60.0);
 
+pub const MAX_LEADER_SCHEDULE_STAKES: Epoch = 5;
+
 type BankStatusCache = StatusCache<Result<()>>;
 
 #[derive(Default)]
@@ -416,7 +418,6 @@ impl Bank {
         );
 
         let leader_schedule_epoch = epoch_schedule.get_leader_schedule_epoch(slot);
-
         if parent.epoch() < new.epoch() {
             if let Some(entered_epoch_callback) =
                 parent.entered_epoch_callback.read().unwrap().as_ref()
@@ -425,14 +426,7 @@ impl Bank {
             }
         }
 
-        // update epoch_stakes cache
-        //  if my parent didn't populate for this staker's epoch, we've
-        //  crossed a boundary
-        if new.epoch_stakes.get(&leader_schedule_epoch).is_none() {
-            new.epoch_stakes
-                .insert(leader_schedule_epoch, new.stakes.read().unwrap().clone());
-        }
-
+        new.update_epoch_stakes(leader_schedule_epoch);
         new.ancestors.insert(new.slot(), 0);
         new.parents().iter().enumerate().for_each(|(i, p)| {
             new.ancestors.insert(p.slot(), i + 1);
@@ -541,6 +535,20 @@ impl Bank {
         self.store_account(&sysvar::slot_hashes::id(), &slot_hashes.create_account(1));
     }
 
+    fn update_epoch_stakes(&mut self, leader_schedule_epoch: Epoch) {
+        // update epoch_stakes cache
+        //  if my parent didn't populate for this staker's epoch, we've
+        //  crossed a boundary
+        if self.epoch_stakes.get(&leader_schedule_epoch).is_none() {
+            self.epoch_stakes.retain(|&epoch, _| {
+                epoch >= leader_schedule_epoch.saturating_sub(MAX_LEADER_SCHEDULE_STAKES)
+            });
+
+            self.epoch_stakes
+                .insert(leader_schedule_epoch, self.stakes.read().unwrap().clone());
+        }
+    }
+
     fn update_fees(&self) {
         self.store_account(
             &sysvar::fees::id(),
@@ -1963,6 +1971,68 @@ mod tests {
         assert_eq!(bank1.block_height(), 1);
     }
 
+    #[test]
+    fn test_bank_update_epoch_stakes() {
+        impl Bank {
+            fn epoch_stake_keys(&self) -> Vec<Epoch> {
+                let mut keys: Vec<Epoch> = self.epoch_stakes.keys().map(|k| *k).collect();
+                keys.sort();
+                keys
+            }
+
+            fn epoch_stake_key_info(&self) -> (Epoch, Epoch, usize) {
+                let mut keys: Vec<Epoch> = self.epoch_stakes.keys().map(|k| *k).collect();
+                keys.sort();
+                (*keys.first().unwrap(), *keys.last().unwrap(), keys.len())
+            }
+        }
+
+        let (genesis_config, _mint_keypair) = create_genesis_config(100_000);
+        let mut bank = Bank::new(&genesis_config);
+
+        let initial_epochs = bank.epoch_stake_keys();
+        assert_eq!(initial_epochs, vec![0, 1]);
+
+        for existing_epoch in &initial_epochs {
+            bank.update_epoch_stakes(*existing_epoch);
+            assert_eq!(bank.epoch_stake_keys(), initial_epochs);
+        }
+
+        for epoch in (initial_epochs.len() as Epoch)..MAX_LEADER_SCHEDULE_STAKES {
+            bank.update_epoch_stakes(epoch);
+            assert_eq!(bank.epoch_stakes.len() as Epoch, epoch + 1);
+        }
+
+        assert_eq!(
+            bank.epoch_stake_key_info(),
+            (
+                0,
+                MAX_LEADER_SCHEDULE_STAKES - 1,
+                MAX_LEADER_SCHEDULE_STAKES as usize
+            )
+        );
+
+        bank.update_epoch_stakes(MAX_LEADER_SCHEDULE_STAKES);
+        assert_eq!(
+            bank.epoch_stake_key_info(),
+            (
+                0,
+                MAX_LEADER_SCHEDULE_STAKES,
+                MAX_LEADER_SCHEDULE_STAKES as usize + 1
+            )
+        );
+
+        bank.update_epoch_stakes(MAX_LEADER_SCHEDULE_STAKES + 1);
+        assert_eq!(
+            bank.epoch_stake_key_info(),
+            (
+                1,
+                MAX_LEADER_SCHEDULE_STAKES + 1,
+                MAX_LEADER_SCHEDULE_STAKES as usize + 1
+            )
+        );
+    }
+
     #[test]
     fn test_bank_capitalization() {
         let bank = Arc::new(Bank::new(&GenesisConfig {