Hi. My company have servers that run postgres for storing some logs and
serving django web interfaces for management of the server itself. In the
last days some servers stopped serving the web interface, and syslog show
this error:

Jun 23 04:40:19 django-1 postgres[8790]: [3-1] FATAL: remaining connection
slots are reserved for non-replication superuser connections

So I started looking for the cause:

$ ps auxf
...
postgres 4580 0.7 0.1 305156 19184 ? S Jun01 251:46
/usr/local/pgsql/bin/postmaster -D /usr/local/pgsql/data
postgres 4746 0.0 1.6 305608 274656 ? Ss Jun01 4:09 \_
postgres: checkpointer process
postgres 4747 0.0 1.2 305288 208708 ? Ss Jun01 0:33 \_
postgres: writer process
postgres 4748 0.0 0.0 305288 9300 ? Ss Jun01 0:04 \_
postgres: wal writer process
postgres 4750 0.0 0.0 305972 2376 ? Ss Jun01 0:00 \_
postgres: autovacuum launcher process
postgres 4752 0.1 0.0 23852 1396 ? Ss Jun01 50:54 \_
postgres: stats collector process
postgres 63615 0.0 0.1 307036 22208 ? Ss Jun02 0:00 \_
postgres: db db [local] idle
postgres 22476 0.0 0.0 306368 2576 ? Ss Jun22 0:00 \_
postgres: db db [local] idle
postgres 4521 0.0 0.0 306512 6408 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 4522 0.0 0.0 306512 6412 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 4523 0.0 0.0 306512 6416 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 4524 0.0 0.0 306512 6412 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 4534 0.0 0.0 306512 6152 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 4544 0.0 0.0 306512 6420 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 4552 0.0 0.0 306512 6408 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 4742 0.0 0.0 306512 6400 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 4743 0.0 0.0 306512 6400 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 4766 0.0 0.0 306512 6408 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 4770 0.0 0.0 306512 6144 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 4774 0.0 0.0 306512 6396 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 4783 0.0 0.0 306512 6400 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 4786 0.0 0.0 306512 6376 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 4804 0.0 0.0 306512 6376 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 4812 0.0 0.0 306512 6376 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 4860 0.0 0.0 306512 6356 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 4862 0.0 0.0 306516 6672 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 4868 0.0 0.0 306516 6408 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 4878 0.0 0.0 306516 6684 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 4881 0.0 0.0 306516 6164 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 4882 0.0 0.0 306516 6168 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 4886 0.0 0.0 306500 6524 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 4887 0.0 0.0 306500 6272 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 4889 0.0 0.0 306500 6272 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 4890 0.0 0.0 306500 6276 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 4907 0.0 0.0 306500 6796 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 5131 0.0 0.0 306500 6268 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 5138 0.0 0.0 306512 6116 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 5142 0.0 0.0 306512 6116 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 5143 0.0 0.0 306512 6644 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 5151 0.0 0.0 306512 6120 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 5154 0.0 0.0 306512 6904 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 5155 0.0 0.0 306512 6128 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 5156 0.0 0.0 306512 6120 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 5157 0.0 0.0 306512 6380 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 5162 0.0 0.0 306512 6120 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 5165 0.0 0.0 306512 6384 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 5172 0.0 0.0 306512 6128 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 5174 0.0 0.0 306512 6120 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 5188 0.0 0.0 306512 6124 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 5189 0.0 0.0 306512 6636 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 5190 0.0 0.0 306512 6104 ? Ss 00:13 0:00 \_
postgres: db db [local] idle
postgres 26621 0.0 0.0 306512 6116 ? Ss 12:54 0:00 \_
postgres: db db [local] idle
postgres 9600 0.0 0.0 306512 6120 ? Ss 13:30 0:00 \_
postgres: db db [local] idle

50 connections in idle status, but looking further:

$ cat /proc/4521/stack
[<ffffffff81b59a8a>] unix_stream_recvmsg+0x2b9/0x633
[<ffffffff81acbf27>] __sock_recvmsg_nosec+0x29/0x2b
[<ffffffff81ace30c>] sock_recvmsg+0x65/0x88
[<ffffffff81ace409>] SYSC_recvfrom+0xda/0x134
[<ffffffff81acf4ef>] SyS_recvfrom+0x9/0xb
[<ffffffff81bd4062>] system_call_fastpath+0x16/0x1b
[<ffffffffffffffff>] 0xffffffffffffffff

All connections have stucked in this stack.

The postmaster process:

$ cat /proc/4580/stack
[<ffffffff810ec9fc>] poll_schedule_timeout+0x3e/0x61
[<ffffffff810ed32f>] do_select+0x5ea/0x629
[<ffffffff810ed4f7>] core_sys_select+0x189/0x245
[<ffffffff810ed632>] SyS_select+0x7f/0xb5
[<ffffffff81bd4062>] system_call_fastpath+0x16/0x1b
[<ffffffffffffffff>] 0xffffffffffffffff

Some information about the server:

$ df -lh
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/root 437G 13G 403G 3% /
/dev/sda1 2.0G 204M 1.6G 12% /boot
tmpfs 7.9G 224K 7.9G 1% /run
devtmpfs 7.8G 0 7.8G 0% /dev
shm 7.9G 0 7.9G 0% /dev/shm

$ free -m
total used free shared buffers cached
Mem: 16030 13221 2808 0 10 3486
-/+ buffers/cache: 9725 6304
Swap: 0 0 0

$ cat /proc/cpuinfo
...
processor : 3
vendor_id : GenuineIntel
cpu family : 6
model : 58
model name : Intel(R) Xeon(R) CPU E3-1220 V2 @ 3.10GHz
stepping : 9
microcode : 0x15
cpu MHz : 3092.951
cache size : 8192 KB
...

# postgresql.conf #

external_pid_file = '/tmp/postgres.pid'
listen_addresses = ''
port = 5432
max_connections = 50
unix_socket_directories = '/tmp'
unix_socket_permissions = 0777
bonjour = off
authentication_timeout = 10min
ssl = on
ssl_ciphers = 'DEFAULT:!LOW:!EXP:!MD5:@STRENGTH'
ssl_renegotiation_limit = 512MB
ssl_cert_file = 'server.crt'
ssl_key_file = 'server.key'

shared_buffers = 256MB
temp_buffers = 128MB
work_mem = 256MB
maintenance_work_mem = 256MB
max_stack_depth = 1MB
max_files_per_process = 1000
max_locks_per_transaction = 128
effective_cache_size = 512MB

wal_level = minimal
wal_writer_delay = 500ms
checkpoint_segments = 100
enable_indexscan = on
enable_sort = on

log_destination = 'syslog'
syslog_facility = 'LOCAL0'
syslog_ident = 'postgres'
client_min_messages = error
log_min_messages = error
log_min_error_statement = fatal
log_min_duration_statement = -1
log_timezone = 'Brazil/East'
track_activities = on
track_counts = on
track_io_timing = off

autovacuum = on
autovacuum_max_workers = 1
autovacuum_naptime = 300min
autovacuum_vacuum_threshold = 50
autovacuum_analyze_threshold = 50

search_path = 'public'

datestyle = 'iso, mdy'
intervalstyle = 'postgres'
timezone = 'Brazil/East'

lc_messages = 'C'
lc_monetary = 'C'
lc_numeric = 'C'
lc_time = 'C'

default_text_search_config = 'pg_catalog.english'
restart_after_crash = on

# end conf #

*I really don't know what is happening, why postgres hang and didn't close
the connections. This django web interface is used only for management and
viewing logs, most server have two users only.*

*I've sent this email just to know if one of yours have seen this, or
something like this, before.*

*Thank you!*

--
-----

Bruno Hass
(51) 9280-3627