Allow extra lookahead blocks in the verifier, state, and block commit…

… task queues (#5465)

zebrad/src/components/sync/downloads.rs

@@ -33,12 +33,13 @@ use crate::components::sync::{
 type BoxError = Box<dyn std::error::Error + Send + Sync + 'static>;
 
 /// A multiplier used to calculate the extra number of blocks we allow in the
-/// verifier and state pipelines, on top of the lookahead limit.
+/// verifier, state, and block commit pipelines, on top of the lookahead limit.
 ///
 /// The extra number of blocks is calculated using
 /// `lookahead_limit * VERIFICATION_PIPELINE_SCALING_MULTIPLIER`.
 ///
-/// This allows the verifier and state queues to hold a few extra tips responses worth of blocks,
+/// This allows the verifier and state queues, and the block commit channel,
+/// to hold a few extra tips responses worth of blocks,
 /// even if the syncer queue is full. Any unused capacity is shared between both queues.
 ///
 /// If this capacity is exceeded, the downloader will start failing download blocks with
@@ -48,7 +49,7 @@ type BoxError = Box<dyn std::error::Error + Send + Sync + 'static>;
 /// the rest of the capacity is reserved for the other queues.
 /// There is no reserved capacity for the syncer queue:
 /// if the other queues stay full, the syncer will eventually time out and reset.
-pub const VERIFICATION_PIPELINE_SCALING_MULTIPLIER: usize = 3;
+pub const VERIFICATION_PIPELINE_SCALING_MULTIPLIER: usize = 4;
 
 #[derive(Copy, Clone, Debug)]
 pub(super) struct AlwaysHedge;