[GENERAL] GMT FATAL: remaining connection slots are reserved fornon-replication superuser connections, but I'm using pgBouncer forconnection pooling

Hi there! Please tell me if this isn't the place to post my question, I'm new
in the list.

I'm using PostgreSQL 9.3, I have around 150 databases, and I use pgBouncer
for connection pooling.
My server is a VPS with 8cpus and 24gb of RAM.

My current postgreSQL configuration (resumed) is this:

listen_addresses = '*'
port = 6543
max_connections = 250
shared_buffers = 2GB
effective_cache_size = 6GB
work_mem = 10485kB
maintenance_work_mem = 512MB
checkpoint_segments = 32
checkpoint_completion_target = 0.7
wal_buffers = 16MB
default_statistics_target = 100


In the other hand, my pgBouncer configuration (resumed) is this:

listen_addr = localhost
listen_port = 5432
pool_mode = transaction
server_reset_query = DISCARD ALL
max_client_conn = 10000
default_pool_size = 10
min_pool_size = 2
server_idle_timeout = 30


However, for the last couple of months (total db number has been increasing)
I have these sporadic errors where pgbouncer can't connect to postgresql.
They occurr every day with variable frequency. Every time the error appears,
it does in a different database. Even in those where the activity is almost
none.

Every time the error is triggered, I check the total connections number and
it never goes beyond ~130.
This is how I check, from psql:
select count(*) from pg_stat_activity;

Also I check for inactive connections with this:
select count(*) from pg_stat_activity where (state = 'idle in transaction')
and xact_start is not null;
... but this number is always low, ~8 idle connections.



When the error triggers, I check the postgresql log and I see this:

2017-02-25 09:13:31 GMT FATAL:  remaining connection slots are reserved for
non-replication superuser connections
2017-02-25 09:13:31 GMT FATAL:  remaining connection slots are reserved for
non-replication superuser connections
2017-02-25 09:13:31 GMT FATAL:  remaining connection slots are reserved for
non-replication superuser connections
2017-02-25 09:13:46 GMT FATAL:  remaining connection slots are reserved for
non-replication superuser connections
2017-02-25 09:13:46 GMT FATAL:  remaining connection slots are reserved for
non-replication superuser connections
2017-02-25 09:13:46 GMT FATAL:  remaining connection slots are reserved for
non-replication superuser connections
2017-02-25 09:13:47 GMT FATAL:  remaining connection slots are reserved for
non-replication superuser connections
2017-02-25 09:13:48 GMT FATAL:  remaining connection slots are reserved for
non-replication superuser connections
2017-02-25 09:13:49 GMT FATAL:  remaining connection slots are reserved for
non-replication superuser connections



And if I check the pgbouncer log I see this:

2017-02-25 09:12:37.354 4080 LOG Stats: 24 req/s, in 387979 b/s, out 2657772
b/s,query 146363 us
2017-02-25 09:13:37.355 4080 LOG Stats: 23 req/s, in 382191 b/s, out 2594329
b/s,query 144827 us
2017-02-25 09:14:29.687 4080 ERROR S: login failed: FATAL: remaining
connection slots are reserved for non-replication superuser connections
2017-02-25 09:14:37.355 4080 LOG Stats: 28 req/s, in 383614 b/s, out 2596947
b/s,query 124098 us
2017-02-25 09:14:44.985 4080 ERROR S: login failed: FATAL: remaining
connection slots are reserved for non-replication superuser connections
2017-02-25 09:14:46.290 4080 ERROR S: login failed: FATAL: remaining
connection slots are reserved for non-replication superuser connections
2017-02-25 09:15:37.355 4080 LOG Stats: 26 req/s, in 378113 b/s, out 2717657
b/s,query 164167 us


What am I missing? I will appreciate any tip or suggestion.
Thanks in advance!



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