We have a "thread" field (unfortunately not yet displayed
in cqlsh, but visible in the table) that records the shard
on which a particular event was recorded. Record the scheduling
group as well, as this can be useful to understand where the
query came from.
(cherry picked from commit 3c03b5f66376dca230868e54148ad1c6a1ad0ee2)
051c310f02