PtrVectorBase custom streamer could be made more efficient.
In source:art/Persistency/Common/detail/setPtrVectorBaseStreamer.cc@3cdd32a4#L27, the persistent part of the object is zeroed after writing. When streaming to multiple output files, this leads to inefficiency. Instead,
PtrVectorBase::fill_offsets() should detect whether the persistent container is already filled, and return after having done nothing.