Connections dropping while using Postgres backend DB with Ejabberd

Greetings,

I was trying to use postgresql database as a backend with Ejabberd XMPP server for load test (Using TSUNG).

Noticed, while using Mnesia the  “simultaneous users and open TCP/UDP connections”  graph in Tsung report is showing consistency, but while using Postgres, we see drop in connections during 100 to 500 seconds of runtime, and then recovering and staying consistent.

I have been trying to figure out what the issue could be without any success. I am kind of a noob in this technology, and hoping for some help from the good people from the community to understand the problem and how to fix this. Below are some details..

·         Postgres server utilization is low ( Avg load 1, Highest Cpu utilization 26%, lowest freemem  9000)

Tsung  graph:

 

                          Graph 2: Mnesia backend                              

·         Ejabberd Server: Ubuntu 16.04, 16 GB ram, 4 core CPU.

·         Postgres on remote server: same config

·         Errors encountered during the same time:  error_connect_etimedout (same outcome for other 2 tests)

·         Tsung Load:  512 Bytes message size, user arrival rate 50/s, 80k registered users.

·         Postgres server utilization is low ( Avg load 1, Highest Cpu utilization 26%, lowest freemem  9000)

·         Same tsung.xm and userlist used for the tests in Mnesia and Postgres.

Postgres Configuration used:shared_buffers = 4GB
effective_cache_size = 12GB
maintenance_work_mem = 1GB
checkpoint_completion_target = 0.9
wal_buffers = 16MB
default_statistics_target = 100
random_page_cost = 4
effective_io_concurrency = 2
work_mem = 256MB
min_wal_size = 1GB
max_wal_size = 2GB
max_worker_processes = 4
max_parallel_workers_per_gather = 2
max_parallel_workers = 4
max_parallel_maintenance_workers = 2