@Override
    public void sweep() {
        LOGGER.logDurationIfDebugEnabled(
                cache::evictExpiredElements,
                "sweep()");
    }
This is called by the lifecycle service and remove writers that are past their TTL, TTI or LRU
items that exceed the capacity.
stroom-index/stroom-index-impl/src/main/java/stroom/index/impl/IndexShardWriterCacheImpl.java