public B maxTraceCols(int maxTraceCols) {
    if (maxTraceCols <= 0) throw new IllegalArgumentException("maxTraceCols <= 0");
    this.maxTraceCols = maxTraceCols;
    return (B) this;
  }
Spans have multiple values for the same id. For example, a client and server contribute to the
same span id. When searching for spans by id, the amount of results may be larger than the ids.
This defines a threshold which accommodates this situation, without looking for an unbounded
number of results.
zipkin-storage/cassandra/src/main/java/zipkin2/storage/cassandra/CassandraStorageBuilder.java