postgresql_connections.sql

We used this query to find out the number of pg connections, 

select count(*) from pg_stat_activity

We investigated and found out the there were multiple(upto 17) pg connections from 2 sidekiq processes 
we have with 40 concurrent threads.

We used this query to find out sidekiq pg connections,

select  pid, usename, application_name, state from pg_stat_activity where usename = 'ringmdstaging' and application_name like 'sidekiq%';
select  count(*) where usename = 'ringmdstaging' and application_name like 'sidekiq%';

We found that the 'max_connections' config variable in /opt/bitnami/postgresql/conf/postgresql.conf is 100.
Then we increased that to 250.

We wrote a shell script to establish 250 pg connections using this,

for i in {1..250}
do
  psql -U postgres &
done

Then this query output 250 pg connections.

postgres=# select  count(*) from pg_stat_activity ;
 count
-------
   250
(1 row)

We tried rails console, We got FATAL:  sorry, too many clients already (PG::ConnectionBad)

Then we killed the duplicate pg connections and tried rails console, it worked.

Though this is not the same error, our initial error was "FATAL: remaining connection slots are reserved 
for non-replication superuser connections", this github issue seem to prove that "max_connections" fixes this,

https://github.com/Netflix/security_monkey/issues/185

This is a temporary fix, a permanent fix to this is to setup Postgres Pooling.

https://wiki.postgresql.org/wiki/Replication,_Clustering,_and_Connection_Pooling

Thanks - Duc & Senthil.