Skip creating child lookup if parent is never created (#5803)

* Skip creating child lookup if parent is never created

beacon_node/network/src/sync/block_lookups/mod.rs

@@ -298,9 +298,12 @@ impl<T: BeaconChainTypes> BlockLookups<T> {
         };
 
         let result = lookup.continue_requests(cx);
-        self.on_lookup_result(id, result, "new_current_lookup", cx);
-        self.update_metrics();
-        true
+        if self.on_lookup_result(id, result, "new_current_lookup", cx) {
+            self.update_metrics();
+            true
+        } else {
+            false
+        }
     }
 
     /* Lookup responses */
@@ -622,15 +625,16 @@ impl<T: BeaconChainTypes> BlockLookups<T> {
     }
 
     /// Common handler a lookup request error, drop it and update metrics
+    /// Returns true if the lookup is created or already exists
     fn on_lookup_result(
         &mut self,
         id: SingleLookupId,
         result: Result<LookupResult, LookupRequestError>,
         source: &str,
         cx: &mut SyncNetworkContext<T>,
-    ) {
+    ) -> bool {
         match result {
-            Ok(LookupResult::Pending) => {} // no action
+            Ok(LookupResult::Pending) => true, // no action
             Ok(LookupResult::Completed) => {
                 if let Some(lookup) = self.single_block_lookups.remove(&id) {
                     debug!(self.log, "Dropping completed lookup"; "block" => ?lookup.block_root(), "id" => id);
@@ -641,12 +645,14 @@ impl<T: BeaconChainTypes> BlockLookups<T> {
                 } else {
                     debug!(self.log, "Attempting to drop non-existent lookup"; "id" => id);
                 }
+                false
             }
             Err(error) => {
                 debug!(self.log, "Dropping lookup on request error"; "id" => id, "source" => source, "error" => ?error);
                 metrics::inc_counter_vec(&metrics::SYNC_LOOKUP_DROPPED, &[error.into()]);
                 self.drop_lookup_and_children(id);
                 self.update_metrics();
+                false
             }
         }
     }