private static Set<List<Boolean>> cacheRollUpPerms(final int tagCount) {
        final Set<List<Boolean>> permsSet = buildRollUpPermutations(tagCount);

        permsMap.put(tagCount, permsSet);

        for (final List<Boolean> perm : permsSet) {
            final SortedSet<Integer> positionList = buildPositionList(perm);

            positionListToObjectMap.put(positionList, RollUpBitMask.buildMaskFromTagPositions(positionList));
        }

        return permsSet;
    }
Cache the perms in two static maps for a given number of tags

@param tagCount
@return
stroom-statistics/stroom-statistics-impl-hbase/src/main/java/stroom/statistics/impl/hbase/rollup/RollUpBitMask.java