Skip to content
On this page

Performance Tuning (Linux)

This guide includes in general tuning suggestions for benchmark and deployment.

Turn Off Swap

Linux swap partitions may cause nondeterministic memory latency to an Erlang virtual machine, significantly affecting the system stability. It is recommended to turn off the swap permanently.

To turn off swap immediately, execute the command sudo swapoff -a. To turn off swap permanently, comment out the swap line in /etc/fstab and reboot the host.

Linux Kernel Tuning

The system-wide limit on max opened file handles:

# 2 millions system-wide
sysctl -w fs.file-max=2097152
sysctl -w fs.nr_open=2097152
echo 2097152 > /proc/sys/fs/nr_open

The limit on opened file handles for the current session:

ulimit -n 2097152


Persist 'fs.file-max' configuration to /etc/sysctl.conf:

fs.file-max = 2097152

Set the maximum number of file handles for the service in /etc/systemd/system.conf:



Set the maximum number of file handles for emqx service in one of the below paths depending on which Linux distribution is used.

  • /usr/lib/systemd/system/emqx.service
  • /lib/systemd/system/emqx.service


Persist the maximum number of opened file handles for users in /etc/security/limits.conf:

*      soft   nofile      2097152
*      hard   nofile      2097152

TCP Network Tuning

Increase the number of incoming connections backlog:

sysctl -w net.core.somaxconn=32768
sysctl -w net.ipv4.tcp_max_syn_backlog=16384
sysctl -w net.core.netdev_max_backlog=16384

Local port range

sysctl -w net.ipv4.ip_local_port_range='1024 65535'

TCP Socket read/write buffer:

sysctl -w net.core.rmem_default=262144
sysctl -w net.core.wmem_default=262144
sysctl -w net.core.rmem_max=16777216
sysctl -w net.core.wmem_max=16777216
sysctl -w net.core.optmem_max=16777216

#sysctl -w net.ipv4.tcp_mem='16777216 16777216 16777216'
sysctl -w net.ipv4.tcp_rmem='1024 4096 16777216'
sysctl -w net.ipv4.tcp_wmem='1024 4096 16777216'

TCP connection tracking:

sysctl -w net.nf_conntrack_max=1000000
sysctl -w net.netfilter.nf_conntrack_max=1000000
sysctl -w net.netfilter.nf_conntrack_tcp_timeout_time_wait=30

TIME-WAIT Bucket Pool, Recycling, and Reuse:

sysctl -w net.ipv4.tcp_max_tw_buckets=1048576

# Enabling following option is not recommended. It could cause connection reset under NAT
# sysctl -w net.ipv4.tcp_tw_recycle=1
# sysctl -w net.ipv4.tcp_tw_reuse=1

Timeout for FIN-WAIT-2 Sockets:

sysctl -w net.ipv4.tcp_fin_timeout=15

Erlang VM Tuning

Tune and optimize the Erlang VM in etc/emq.conf file: :

## Erlang Process Limit
node.process_limit = 2097152

## Sets the maximum number of simultaneously existing ports for this system
node.max_ports = 2097152

EMQX Tuning

Tune the acceptor pool size and max_connections limit in etc/emqx.conf.

E.g, for TCP listeners:

## TCP Listener
listeners.tcp.$name.acceptors = 64
listeners.tcp.$name.max_connections = 1024000

Client Machine Tuning

Tune the client machine to benchmark EMQX:

sysctl -w net.ipv4.ip_local_port_range="500 65535"
echo 1000000 > /proc/sys/fs/nr_open
ulimit -n 100000

MQTT Benchmarking

Test tools for concurrent connections: emqtt_bench.