Allow user to set an epoch margin for pruning

beacon_node/store/src/config.rs

@@ -9,6 +9,7 @@ pub const DEFAULT_SLOTS_PER_RESTORE_POINT: u64 = 8192;
 pub const DEFAULT_BLOCK_CACHE_SIZE: usize = 5;
 pub const DEFAULT_BLOB_CACHE_SIZE: usize = 5;
 pub const DEFAULT_EPOCHS_PER_BLOB_PRUNE: u64 = 1;
+pub const DEFAULT_BLOB_PUNE_MARGIN_EPOCHS: Option<u64> = None;
 
 /// Database configuration parameters.
 #[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
@@ -29,8 +30,11 @@ pub struct StoreConfig {
     pub prune_payloads: bool,
     /// Whether to prune blobs older than the blob data availability boundary.
     pub prune_blobs: bool,
-    /// Frequency of blob pruning. Default: every epoch.
+    /// Frequency of blob pruning in epochs. Default: every epoch.
     pub epochs_per_blob_prune: u64,
+    /// The margin for blob pruning in epochs. The oldest blobs are pruned up until
+    /// data_availability_boundary - blob_prune_margin_epochs. Default: 0.
+    pub blob_prune_margin_epochs: Option<u64>,
 }
 
 /// Variant of `StoreConfig` that gets written to disk. Contains immutable configuration params.
@@ -57,6 +61,7 @@ impl Default for StoreConfig {
             prune_payloads: true,
             prune_blobs: true,
             epochs_per_blob_prune: DEFAULT_EPOCHS_PER_BLOB_PRUNE,
+            blob_prune_margin_epochs: DEFAULT_BLOB_PUNE_MARGIN_EPOCHS,
         }
     }
 }

beacon_node/store/src/hot_cold_store.rs

@@ -1798,8 +1798,20 @@ impl<E: EthSpec, Hot: ItemStore<E>, Cold: ItemStore<E>> HotColdDB<E, Hot, Cold>
 
         let mut ops = vec![];
         let mut last_pruned_block_root = None;
-        // Prune up until the data availability boundary.
-        let end_slot = (data_availability_boundary - 1).end_slot(E::slots_per_epoch());
+
+        // At most prune up until the data availability boundary epoch, leaving at least blobs in
+        // the data availability boundary epoch and younger.
+        let end_slot = {
+            let earliest_prunable_epoch = data_availability_boundary - 1;
+            // Stop pruning before reaching the data availability boundary if a margin is
+            // configured.
+            let end_epoch = if let Some(margin) = self.get_config().blob_prune_margin_epochs {
+                earliest_prunable_epoch - margin
+            } else {
+                earliest_prunable_epoch
+            };
+            end_epoch.end_slot(E::slots_per_epoch())
+        };
 
         for res in self.forwards_block_roots_iterator_until(
             oldest_blob_slot,