public Duration getAverageFileListDuration() {
        if (fileListDuration.isZero()) {
            return Duration.ZERO;
        } else {
            // Each cache miss corresponds to a file list action so we use it to get the average
            return fileListDuration.dividedBy(cacheMissCount.longValue());
        }
    }
Only call this once per meta
stroom-data/stroom-data-store-impl-fs/src/main/java/stroom/data/store/impl/fs/FsOrphanMetaFinderProgress.java