public boolean hasNGramIndices() {
        if (frozen) return hasNGramIndices;
        for (Map.Entry<String,SearchDefinition> searchDefinition : searchDefinitions.entrySet()) {
            for (Index index : searchDefinition.getValue().indices().values())
                if (index.isNGram()) return true;
        }
        return false;
    }
Whether this contains any index which has isNGram()==true. This is free to ask on a frozen instance.
container-search/src/main/java/com/yahoo/prelude/IndexFacts.java