public StorageID appendMutant(final String[] source, final String value) {
        if (sealed) {
            throw new IllegalStateException("The storage ID is sealed. Can't append a new fragment, source=" + Arrays.toString(source));
        }
        fragments.add(new Fragment(source, String.class, true, value));
        return this;
    }
The string ID would only be built once.
oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/storage/StorageID.java