presto-accumulo/src/main/java/io/prestosql/plugin/accumulo/index/Indexer.java/Indexer/addIndexMutation
class Indexer:    private void addIndexMutation(ByteBuffer row, ByteBuffer family, ColumnVisibility visibility, byte[] qualifier)
    {
        // Create the mutation and add it to the batch writer
        Mutation indexMutation = new Mutation(row.array());
        indexMutation.put(family.array(), qualifier, visibility, EMPTY_BYTES);
        try {
            indexWriter.addMutation(indexMutation);
        }
        catch (MutationsRejectedException e) {
            throw new PrestoException(UNEXPECTED_ACCUMULO_ERROR, "Index mutation rejected by server", e);
        }

        // Increment the cardinality metrics for this value of index
        // metrics is a mapping of row ID to column family
        MetricsKey key = new MetricsKey(row, family, visibility);
        AtomicLong count = metrics.get(key);
        if (count == null) {
            count = new AtomicLong(0);
            metrics.put(key, count);
        }

        count.incrementAndGet();
    }