message: perf(sync): use last header as base to avoid scan from tip.
diff: @@ -386,7 +386,7 @@ impl<CS: ChainStore> SyncSharedState<CS> {
  let mut step = 1;
  let mut locator = Vec::with_capacity(32);
  let mut index = start.number();
  - let base = start.hash();
  + let mut base = start.hash();
  loop {
  let header = self
  .get_ancestor(&base, index)
  @@ -405,6 +405,7 @@ impl<CS: ChainStore> SyncSharedState<CS> {
  break;
  }
  index -= step;
  + base = header.hash();
  }
  locator
  }
  