public Set<String> getAvailableChildStreamTypes(final long id, final long partNo) {
        return securityContext.useAsReadResult(() -> {
            try (final Source source = streamStore.openSource(id, true)) {
                if (source == null) {
                    throw new RuntimeException(LogUtil.message("Error opening stream {} - meta not found.", id));
                }

                try (final InputStreamProvider inputStreamProvider = source.get(partNo)) {
                    return inputStreamProvider.getChildTypes();
                }
            } catch (IOException e) {
                throw new RuntimeException(LogUtil.message("Error opening stream {}, part {}", id, partNo), e);
            }
        });
    }
How big our buffers are. This should always be a multiple of 8.
stroom-data/stroom-data-store-impl/src/main/java/stroom/data/store/impl/DataFetcher.java