[root@tvr1-pgm-svp-01 ~]# ss -tenp | grep 18216
ESTAB      0      0              10.69.64.164:5432          10.69.64.118:63458  timer:(keepalive,1.634ms,0) users:(("postgres",18216,11)) uid:26 ino:1372166028 sk:ffff880253ff2580 <->

postgres=# select * from pg_stat_activity where pid = 18216;
-[ RECORD 1 ]----+--------------------------------------------------------------------------------------------------------------------------
datid            | 26014
datname          | svp
pid              | 18216
usesysid         | 17822
usename          | svp
application_name | Passenger RubyApp: /var/www/rc-simple-print/current/public
client_addr      | 10.69.64.118
client_hostname  |
client_port      | 63458
backend_start    | 2017-04-12 22:02:03.274406+00
xact_start       | 2017-04-12 22:02:03.341284+00
query_start      | 2017-04-12 22:03:19.092631+00
state_change     | 2017-04-12 22:03:19.092632+00
waiting          | f
state            | active
backend_xid      |
backend_xmin     |
query            | SELECT count(*) FROM pg_catalog.pg_class AS c WHERE c.oid = to_regclass('"route_card_points"') AND c.relpersistence = 'u'

postgres=# \q

[root@tvr1-pgm-svp-01 etc]# gdb -p 18216 /usr/pgsql-9.4/bin/postgres
GNU gdb (GDB) Red Hat Enterprise Linux 7.6.1-80.el7
Copyright (C) 2013 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-redhat-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /usr/pgsql-9.4/bin/postgres...


Missing separate debuginfos, use: debuginfo-install postgresql94-server-9.4.5-2PGDG.rhel7.x86_64
(gdb)
(gdb)
(gdb) bt
#0  0x00007fa0155f006d in recv () from /lib64/libc.so.6
#1  0x00000000005b9f74 in secure_read ()
#2  0x00000000005c2c1b in pq_recvbuf ()
#3  0x00000000005c3815 in pq_getbyte ()
#4  0x000000000067d9e5 in PostgresMain ()
#5  0x00000000004629c1 in ServerLoop ()
#6  0x000000000062db46 in PostmasterMain ()
#7  0x0000000000463609 in main ()
(gdb) q
A debugging session is active.

	Inferior 1 [process 18216] will be detached.

[root@tvr1-pgm-svp-01 etc]# ls /proc/18216/fd/ -la
total 0
dr-x------ 2 postgres postgres  0 Apr 13 10:18 .
dr-xr-xr-x 8 postgres postgres  0 Apr 13 01:02 ..
lr-x------ 1 postgres postgres 64 Apr 13 10:18 0 -> /dev/null
l-wx------ 1 postgres postgres 64 Apr 13 10:18 1 -> pipe:[164143434]
lrwx------ 1 postgres postgres 64 Apr 13 10:18 10 -> socket:[164143436]
lrwx------ 1 postgres postgres 64 Apr 13 10:18 11 -> socket:[1372166028]
lrwx------ 1 postgres postgres 64 Apr 13 10:18 12 -> /pg/pgdata/tbsdata/PG_9.4_201409291/26014/11950060
lrwx------ 1 postgres postgres 64 Apr 13 10:18 13 -> /pg/pgdata/tbsdata/PG_9.4_201409291/26014/11947958_vm
lrwx------ 1 postgres postgres 64 Apr 13 10:18 19 -> /pg/pgdata/tbsdata/PG_9.4_201409291/26014/11947837
l-wx------ 1 postgres postgres 64 Apr 13 10:18 2 -> pipe:[164143434]
lrwx------ 1 postgres postgres 64 Apr 13 10:18 20 -> /pg/pgdata/tbsdata/PG_9.4_201409291/26014/11950002
lrwx------ 1 postgres postgres 64 Apr 13 10:18 21 -> /pg/pgdata/tbsdata/PG_9.4_201409291/26014/11950003
lr-x------ 1 postgres postgres 64 Apr 13 10:18 3 -> pipe:[1372167704]
l-wx------ 1 postgres postgres 64 Apr 13 10:18 4 -> pipe:[1372167704]
lrwx------ 1 postgres postgres 64 Apr 13 10:18 5 -> /pg/pgdata/tbsdata/PG_9.4_201409291/26014/16897493
lrwx------ 1 postgres postgres 64 Apr 13 10:18 6 -> /var/lib/pgsql/9.4/data/global/43011
lr-x------ 1 postgres postgres 64 Apr 13 10:18 7 -> pipe:[164143433]
lrwx------ 1 postgres postgres 64 Apr 13 10:18 8 -> /pg/pgdata/tbsdata/PG_9.4_201409291/26014/11947958
lrwx------ 1 postgres postgres 64 Apr 13 10:18 9 -> /pg/pgdata/tbsdata/PG_9.4_201409291/26014/11950059
[root@tvr1-pgm-svp-01 etc]# strace -p 18216
Process 18216 attached
recvfrom(11, ^CProcess 18216 detached
 <detached ...>