.. _tune:

============
Tuning Guide
============

Tuning the Linux Kernel, Networking, Erlang VM and the *EMQ* broker for one million concurrent MQTT connections.

-------------------
Linux Kernel Tuning
-------------------

The system-wide limit on max opened file handles::

    # 2 million 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 current session::

    ulimit -n 1048576

/etc/sysctl.conf
----------------

Add the 'fs.file-max' to /etc/sysctl.conf, make the changes permanent::

    fs.file-max = 1048576

/etc/security/limits.conf
-------------------------

Persist the limits on opened file handles for users in /etc/security/limits.conf::

    *      soft   nofile      1048576
    *      hard   nofile      1048576

--------------
Network Tuning
--------------

Increase 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="1000 65535"

Read/Write Buffer for TCP connections::

    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'

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

The TIME-WAIT Buckets Pool, Recycling and Reuse::

    net.ipv4.tcp_max_tw_buckets=1048576

    # Enable fast recycling of TIME_WAIT sockets.  Enabling this
    # option is not recommended for devices communicating with the
    # general Internet or using NAT (Network Address Translation).
    # Since some NAT gateways pass through IP timestamp values, one
    # IP can appear to have non-increasing timestamps.
    # net.ipv4.tcp_tw_recycle = 1
    # net.ipv4.tcp_tw_reuse = 1

Timeout for FIN-WAIT-2 sockets::

    net.ipv4.tcp_fin_timeout = 15

----------------
Erlang VM Tuning
----------------

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

.. code-block:: properties

    ## Erlang Process Limit
    node.process_limit = 2097152

    ## Sets the maximum number of simultaneously existing ports for this system
    node.max_ports = 1048576

--------------
The EMQ Broker
--------------

Tune the acceptor pool, max_clients limit and sockopts for TCP listener in etc/emqttd.config:

.. code-block:: properties

    ## TCP Listener
    mqtt.listener.tcp = 1883
    mqtt.listener.tcp.acceptors = 64
    mqtt.listener.tcp.max_clients = 1000000

--------------
Client Machine
--------------

Tune the client machine to benchmark emqttd broker:

.. code-block:: bash

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

---------------
emqtt_benchmark
---------------

Test tool for concurrent connections: http://github.com/emqtt/emqtt_benchmark