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Performance Tuning (Linux)

Due to the typically large number of devices and data in IoT applications, EMQX, as an MQTT server, is responsible for handling and delivering messages generated by a massive number of devices. In this scenario, optimizing EMQX system performance becomes particularly crucial.

Optimization aims to maximize the following aspects of performance:

  • Message Processing Capability: Enhancing EMQX's ability to process messages quickly and efficiently, ensuring it can rapidly receive, process, and forward device-generated messages.
  • Throughput: Increasing throughput to ensure the system can handle and deliver messages from devices in a timely manner.
  • Stability: Reducing latency under high loads, improving system responsiveness, and lowering the risk of system crashes or failures.

This page provides general tuning suggestions for benchmarking 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/emqx.conf file:

## 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.

For example, 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.