ps -u postgres o pid,rss:8,cmd | awk 'NR>1 {A+=$2} {print} END{print "Total RSS: " A}'

  PID      RSS CMD
 2263     8112 postgres: root production 10.1.1.1(44699)
 2478     7888 postgres: root production 10.1.1.1(44740)
 3486    12060 postgres: root mitel 10.1.1.20(56395)
 5258   245840 postgres: ibroker production 10.1.3.10(60655)
 5262    11440 postgres: root c21mb_ledger 10.1.3.10(60657)
 5955   759728 postgres: ibroker production 10.1.4.100(52832)
 8774     7100 postgres: root texashomes 10.1.1.102(50113)
11137    10624 postgres: root production 10.1.1.20(37557)
11138    10620 postgres: root production 10.1.1.20(37558)
11139    10616 postgres: root production 10.1.1.20(37559)
11140    10616 postgres: root production 10.1.1.20(37560)
11141    10604 postgres: root production 10.1.1.20(37561)
11142    10608 postgres: root production 10.1.1.20(37562)
11168    49032 postgres: root session 10.1.1.20(37566)
11169    49028 postgres: root session 10.1.1.20(37567)
11171    49032 postgres: root session 10.1.1.20(37568)
11172    49028 postgres: root session 10.1.1.20(37569)
11173    48960 postgres: root session 10.1.1.20(37570)
11174    48848 postgres: root session 10.1.1.20(37571)
13605   237056 postgres: ibroker production 10.1.3.44(42043)
13958   950036 postgres: ibroker production 10.1.3.1(60019)
14872     5456 postgres: root dns_internal 127.0.0.1(59540)
14873     5456 postgres: root dns_internal 127.0.0.1(59541)
14876     8988 postgres: root dns_internal 127.0.0.1(59542)
14877     5452 postgres: root dns_internal 127.0.0.1(59543)
14879     8980 postgres: root dns_internal 127.0.0.1(59544)
14880     5452 postgres: root dns_internal 127.0.0.1(59545)
14882     9040 postgres: root dns_internal 127.0.0.1(59546)
14883     5448 postgres: root dns_internal 127.0.0.1(59547)
14895     8992 postgres: root dns_internal 127.0.0.1(59548)
14896     5460 postgres: root dns_internal 127.0.0.1(59549)
15960    13188 postgres: vaquero vaquero 127.0.0.1(59561)
17027     3856 postgres: root production [local]
18157   542004 postgres: ibroker production 10.1.3.3(58493)
21051   621364 postgres: ibroker production 10.1.3.54(10678)
21060     6472 postgres: root c21mb_ledger 10.1.3.54(10680)
26033   104552 postgres: ibroker production 10.1.4.72(58340)
26042     6464 postgres: root c21mb_ledger 10.1.4.72(58342)
27710     8580 postgres: root production 10.1.1.6(46801)
27712     5428 postgres: root session 10.1.1.6(46804)
29737     8580 postgres: root production 10.1.1.6(54798)
29738     5420 postgres: root session 10.1.1.6(54801)
30176   200284 /usr/lib/postgresql/9.3/bin/postgres -D /var/lib/postgresql/9.3/main -c config_file=/etc/postgresql/9.3/main/postgresql.conf
30178  5571684 postgres: checkpointer process
30179   196480 postgres: writer process
30180    10508 postgres: wal writer process
30181     3568 postgres: autovacuum launcher process
30182     3396 postgres: stats collector process
31298   126352 postgres: root production 10.1.1.6(51169)
31302     5420 postgres: root session 10.1.1.6(51171)
31321   171212 postgres: root production 10.1.1.6(51311)
31322     5424 postgres: root session 10.1.1.6(51312)
31364   117460 postgres: root production 10.1.1.6(51503)
31365     5432 postgres: root session 10.1.1.6(51504)
31542    13624 postgres: root production 10.1.1.6(51511)
31543    13620 postgres: root production 10.1.1.6(51521)
31544    40844 postgres: root production 10.1.1.6(51522)
31545    49044 postgres: root session 10.1.1.6(51523)
31553    13624 postgres: root production 10.1.1.6(51544)
31554   171204 postgres: root production 10.1.1.6(51546)
31555     5428 postgres: root session 10.1.1.6(51549)
32607   765032 postgres: ibroker production 10.1.4.106(49210)