Issues with EPOCH-s, TIMESTAMP(TZ)-s and leap seconds.

Hi all,

I'm having trouble understanding matters related to TIMESTAMP(TZ)-s and
leap seconds - my machine runs on UTC so as to remove any issues related
to the zones.

From here: https://en.wikipedia.org/wiki/Leap_second,

There have been 27 leap seconds added to UTC since 1972.

But, when I run this fiddle (see bottom of this email link)

https://dbfiddle.uk/wxvmzfJb

(first snippet - 2015 -> 2016) I get a "nice" even number for the EPOCH
of, 00:00:00 2016 , say (= 1451606400) - now, with 27 leap seconds since
1972, I would expect that number to be (something like) 1451606427?

I thought that the EPOCH was the number of seconds since 1970-01-01
00:00:00? Is this incorrect?

Also, (first snippet again), why is the TIMESTAMPTZ 23:59:60 2015 even
allowed?

Now, we come to the second snippet (2016 -> 2017), I get *_exactly_* the
same behaviour!

I was expecting to see that '2016-12-31 23:59:60'::TIMESTAMPTZ would
work (leap second) and then that '2017-01-01 00:00:00'::TIMESTAMPTZ
would have incremented by 1 second?

I'm puzzled. Does PostgreSQL take leap seconds into account? Does anyone?

Any help, advice, recommendations, URL-s, references &c. appreciated.

E...