Github user simonellistonball commented on the issue:
https://github.com/apache/metron/pull/1233
@ottobackwards wouldn't ISO constant support require us to do a check on
the string before passing to the DateFormat instance, which on something that
is likely to be run A LOT (i.e. multiple times for every message) could
actually be a significant for performance, which I would say outweighs the
convenience of not having to remember what the format looks like.---
