private static Optional<String> fieldsWithHnswIndex(SchemaInfo schema) {
        var fields = schema.fullSchema()
                           .allFields()
                           .filter(HnswValidator::hasHnswIndex)
                           .map(ImmutableSDField::getName)
                           .sorted()
                           .toList();
        if (fields.isEmpty()) return Optional.empty();

        return Optional.of("fields %s in schema %s".formatted(String.join(", ", fields), schema.name()));
    }
Validates hnsw settings and warns if using hnsw and having searchable copies > 1 for a content cluster

@author hmusum
config-model/src/main/java/com/yahoo/vespa/model/application/validation/HnswValidator.java