Bound min size of dynamic processor queues (#6466)

* Bound min size of dynamic processor queues

* Use max

* Add test

beacon_node/beacon_processor/src/lib.rs

@@ -93,6 +93,11 @@ const DEFAULT_MAX_SCHEDULED_WORK_QUEUE_LEN: usize = 3 * DEFAULT_MAX_WORK_EVENT_Q
 /// slightly, we don't need to adjust the queues during the lifetime of a process.
 const ACTIVE_VALIDATOR_COUNT_OVERPROVISION_PERCENT: usize = 110;
 
+/// Minimum size of dynamically sized queues. Due to integer division we don't want 0 length queues
+/// as the processor won't process that message type. 128 is an arbitrary value value >= 1 that
+/// seems reasonable.
+const MIN_QUEUE_LEN: usize = 128;
+
 /// Maximum number of queued items that will be stored before dropping them
 pub struct BeaconProcessorQueueLengths {
     aggregate_queue: usize,
@@ -155,9 +160,15 @@ impl BeaconProcessorQueueLengths {
             aggregate_queue: 4096,
             unknown_block_aggregate_queue: 1024,
             // Capacity for a full slot's worth of attestations if subscribed to all subnets
-            attestation_queue: active_validator_count / slots_per_epoch,
+            attestation_queue: std::cmp::max(
+                active_validator_count / slots_per_epoch,
+                MIN_QUEUE_LEN,
+            ),
             // Capacity for a full slot's worth of attestations if subscribed to all subnets
-            unknown_block_attestation_queue: active_validator_count / slots_per_epoch,
+            unknown_block_attestation_queue: std::cmp::max(
+                active_validator_count / slots_per_epoch,
+                MIN_QUEUE_LEN,
+            ),
             sync_message_queue: 2048,
             sync_contribution_queue: 1024,
             gossip_voluntary_exit_queue: 4096,
@@ -1686,3 +1697,21 @@ impl Drop for SendOnDrop {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use types::{BeaconState, ChainSpec, Eth1Data, ForkName, MainnetEthSpec};
+
+    #[test]
+    fn min_queue_len() {
+        // State with no validators.
+        let spec = ForkName::latest().make_genesis_spec(ChainSpec::mainnet());
+        let genesis_time = 0;
+        let state = BeaconState::<MainnetEthSpec>::new(genesis_time, Eth1Data::default(), &spec);
+        assert_eq!(state.validators().len(), 0);
+        let queue_lengths = BeaconProcessorQueueLengths::from_state(&state, &spec).unwrap();
+        assert_eq!(queue_lengths.attestation_queue, MIN_QUEUE_LEN);
+        assert_eq!(queue_lengths.unknown_block_attestation_queue, MIN_QUEUE_LEN);
+    }
+}