Compaction of an ordered event stream (OES) is disclosed. An OES storage system can employing multiple tiers of storage devices, wherein the different tiers each can provide certain advantages and disadvantages that can be used to balance OES event storage costs, both monetarily and in terms of computing resource burden. Compaction can be facilitated by storing, in a stream map, a reference to an event stored via a second tier of storage in contrast to storing in the stream map actual events of a first tier of storage. A reference can be enabled by storing events in a chunk body and storing a location relationships in a header of the chunk. The stream map can then search headers for references, which can often be smaller than the events themselves, which references can then be communicated, stored, and updated in the stream map to facilitate OES compaction.