hollow/src/main/java/com/netflix/hollow/tools/history/HollowHistory.java
public void deltaOccurred(long newVersion) {
        keyIndex.update(latestHollowReadStateEngine, true);

        HollowHistoricalStateDataAccess historicalDataAccess = creator.createBasedOnNewDelta(latestVersion, latestHollowReadStateEngine);
        historicalDataAccess.setNextState(latestHollowReadStateEngine);

        HollowHistoricalStateKeyOrdinalMapping keyOrdinalMapping = createKeyOrdinalMappingFromDelta();
        HollowHistoricalState historicalState = new HollowHistoricalState(newVersion, keyOrdinalMapping, historicalDataAccess, latestHeaderEntries);

        addHistoricalState(historicalState);
        this.latestVersion = newVersion;
        this.latestHeaderEntries = latestHollowReadStateEngine.getHeaderTags();
    }
public void deltaOccurred(long newVersion) {
        keyIndex.update(latestHollowReadStateEngine, true);

        HollowHistoricalStateDataAccess historicalDataAccess = creator.createBasedOnNewDelta(latestVersion, latestHollowReadStateEngine);
        historicalDataAccess.setNextState(latestHollowReadStateEngine);

        HollowHistoricalStateKeyOrdinalMapping keyOrdinalMapping = createKeyOrdinalMappingFromDelta();
        HollowHistoricalState historicalState = new HollowHistoricalState(newVersion, keyOrdinalMapping, historicalDataAccess, latestHeaderEntries);

        addHistoricalState(historicalState);
        this.latestVersion = newVersion;
        this.latestHeaderEntries = latestHollowReadStateEngine.getHeaderTags();
    }
Call this method after each time a delta occurs in the backing {@link HollowReadStateEngine}.  This
is how the HollowHistory knows how to create a new {@link HollowHistoricalState}.

@param newVersion The version of the new state