Custom SpaceDataSource and FIFO persistence

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How do we retain FIFO information across system restarts when using our own custom SpaceDataSource? Is the FIFO information somehow relayed to the SpaceDataSource during mirroring? Or do we ourselves have to keep track of the ordering of space objects as they are received by our SpaceDataSource?

Is it safe to assume that the space will build a new FIFO index on restart from the ordering of objects as they are received during InitialLoad?