I noticed this today on my 9.4.2 server running on FreeBSD 10.1:
Jun 5 18:59:40 slocum postgres[986]: [3957-1] LOG: could not truncate directory "pg_subtrans": apparent wraparound
Looking at a post from 2010, Tom Lane suggest this information was useful:
[root@slocum:/usr/local/pgsql/data/pg_subtrans] # ls -l
total 1
-rw------- 1 pgsql pgsql 8192 Jun 5 19:04 0032
This not not a high throughput server.
—
Dan Langille
http://langille.org/