ERROR: out of memory

Hey folks,
I have 4 postgresql servers 9.3.6(on master I use 9.3.5) configured with
streaming replication - with 1 maser(30GB RAM, processor - Intel Xeon
E5-2680 v2) and 3 slaves(61 Intel Xeon E5-2670 v2), all on Ubuntu 14.04.1
LTS,

Master configuration:
default_statistics_target = 50

maintenance_work_mem = 1GB

constraint_exclusion = on

checkpoint_completion_target = 0.9

effective_cache_size = 22GB

work_mem = 120MB

wal_buffers = 8MB

checkpoint_segments = 16

shared_buffers = 7GB

max_connections = 300

Slave configuration:

max_connections = 300

shared_buffers = 10GB

effective_cache_size = 45GB

work_mem = 19660kB

maintenance_work_mem = 2GB

checkpoint_segments = 32

checkpoint_completion_target = 0.7

wal_buffers = 16MB

default_statistics_target = 100

I am using XSF file system, size of my database ­ 168GB.

For linux kernel I have settings:

vm.swappiness = 0

vm.overcommit_memory = 2

vm.overcommit_ratio = 50

kernel.shmall = 7864320
kernel.shmmax = 32212254720

kernel.shmmni = 4096

Master is primary to write data. Slave ­ for reporting. In reality I am
using not more then 100 connections to slave server at the same time.
Writing about 3000 records in a minute.

I have one table where I writing statistics, that is portioned by month.
Below is table size with biggest relations

public.stats_201408 | 9212 MB

public.stats_201503 | 8868 MB

pg_toast.pg_toast_6404464 | 8319 MB

pg_toast.pg_toast_317921 | 7520 MB

public.stats_201409 | 7101 MB

public.stats_201412 | 4458 MB

I see here pg_toast, from doc I read it¹s large objects there, but It¹s not
related to my table stats, which is read/write heavy(type of the biggest
column in this table => character varying(3000)). I.e. - it¹s related to
different table.

My application create 100 connections & keeping them during whole life
cycle(usually until next deploy ­ that may happen in couple days), with time
­ connection growing in memory(checking using htop) & free memory going
down. As result with time(usually 3-4 hours) my DB start throwing

ERROR: out of memory

DETAIL: Failed on request of size 2048.

After I restart my application(reconnect to DB), it start working fine
again.

It even fail on simple query like:

SELECT COUNT(*) FROM ³stats" WHERE "stats²."bt_id" = $1 AND
(stats.created_at >= '2015-04-02 04:00:00.000000') AND (stats.created_at <=
'2015-04-03 03:59:59.999999') AND ("stats"."source" IS NOT NULL) AND
"stats"."device" IN (1, 2) AND "stats²."ra" = 0 AND "stats"."paid" = ¹t'

Any help appreciated.