hollow/src/main/java/com/netflix/hollow/core/memory/ByteArrayOrdinalMap.java
private int findFreeOrdinal(int preferredOrdinal) {
        if (preferredOrdinal != -1 && unusedPreviousOrdinals.get(preferredOrdinal)) {
            unusedPreviousOrdinals.clear(preferredOrdinal);
            return preferredOrdinal;
        }

        return freeOrdinalTracker.getFreeOrdinal();
    }
private int findFreeOrdinal(int preferredOrdinal) {
        if (preferredOrdinal != -1 && unusedPreviousOrdinals.get(preferredOrdinal)) {
            unusedPreviousOrdinals.clear(preferredOrdinal);
            return preferredOrdinal;
        }

        return freeOrdinalTracker.getFreeOrdinal();
    }
If the preferredOrdinal has not already been used, mark it and use it.  Otherwise,
delegate to the FreeOrdinalTracker.