Allow user to set an epoch margin for pruning

beacon_node/client/src/config.rs

@@ -201,6 +201,10 @@ impl Config {
     pub fn create_data_dir(&self) -> Result<PathBuf, String> {
         ensure_dir_exists(self.get_data_dir())
     }
+
+    pub fn get_blob_prune_margin_epochs(&self) -> Option<u64> {
+        self.store.blob_prune_margin_epochs
+    }
 }
 
 /// Ensure that the directory at `path` exists, by creating it and all parents if necessary.

beacon_node/src/cli.rs

@@ -568,6 +568,14 @@ pub fn cli_app<'a, 'b>() -> App<'a, 'b> {
                 .takes_value(true)
                 .default_value("1")
         )
+        .arg(
+            Arg::with_name("blob-prune-margin-epochs")
+                .long("blob-prune-margin-epochs")
+                .help("The margin for blob pruning in epochs. The oldest blobs are pruned \
+                       up until data_availability_boundary - blob_prune_margin_epochs.")
+                .takes_value(true)
+                .default_value("0")
+        )
 
         /*
          * Misc.

beacon_node/src/config.rs

@@ -421,6 +421,14 @@ pub fn get_config<E: EthSpec>(
         client_config.store.epochs_per_blob_prune = epochs_per_blob_prune;
     }
 
+    if let Some(blob_prune_margin_epochs) =
+        clap_utils::parse_optional(cli_args, "blob-prune-margin-epochs")?
+    {
+        if blob_prune_margin_epochs > 0 {
+            client_config.store.blob_prune_margin_epochs = Some(blob_prune_margin_epochs);
+        }
+    }
+
     /*
      * Zero-ports
      *

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,

database_manager/src/lib.rs

@@ -94,6 +94,16 @@ pub fn cli_app<'a, 'b>() -> App<'a, 'b> {
                 .help("Data directory for the freezer database.")
                 .takes_value(true),
         )
+        .arg(
+            Arg::with_name("blob-prune-margin-epochs")
+                .long("blob-prune-margin-epochs")
+                .help(
+                    "The margin for blob pruning in epochs. The oldest blobs are pruned \
+                       up until data_availability_boundary - blob_prune_margin_epochs.",
+                )
+                .takes_value(true)
+                .default_value("0"),
+        )
         .subcommand(migrate_cli_app())
         .subcommand(version_cli_app())
         .subcommand(inspect_cli_app())
@@ -117,6 +127,14 @@ fn parse_client_config<E: EthSpec>(
     client_config.store.slots_per_restore_point = sprp;
     client_config.store.slots_per_restore_point_set_explicitly = sprp_explicit;
 
+    if let Some(blob_prune_margin_epochs) =
+        clap_utils::parse_optional(cli_args, "blob-prune-margin-epochs")?
+    {
+        if blob_prune_margin_epochs > 0 {
+            client_config.store.blob_prune_margin_epochs = Some(blob_prune_margin_epochs);
+        }
+    }
+
     Ok(client_config)
 }