[rabbitmq-discuss] RabbitMQ memory management

Sun Sep 14 11:53:13 BST 2008

Matthias,

On Sat, Sep 13, 2008 at 11:28 AM, Matthias Radestock
<matthias at lshift.net> wrote:
>
> Alexis Richardson wrote:
>
>> * provide a means to tell producers to back off, or alert an operator
>
> The easiest solution I can think of is to
>
> 1) configure Erlang's memsup
> (http://www.erlang.org/doc/apps/os_mon/index.html) to trigger alarms
> when memory consumption gets tight.
>
> This can be done without any code change; in the rabbitmq-server startup
> script simply change the "-os_mon start_memsup false" to "true" and
> adjust the thresholds with additional options of the form "-memsup
> <param> <value>"
>
> When a threshold is reached, a message like this will appear in the
> rabbit.log:
>
> =INFO REPORT==== 13-Sep-2008::10:59:37 ===
>     alarm_handler: {set,{process_memory_high_watermark,<0.31.0>}}
>
> When the memory usage drops below the threshold again a similar message
> is logged.
>
> One can also set up SNMP monitoring, but that is more complicated.
>
>
> 2) get queues to drop messages when memory consumption is above the
> thresholds.
>
> This does require some coding, but not very much.
>
> We set up an alarm handler that informs all a node's queues when a "high
> memory" alarm is set/cleared. Queues record that information as part of
> their state.
>
> When a message is routed to a queue while the alarm is set, and the
> queue cannot immediately route the message to an auto-ack consumer - in
> other words, the message requires queueing - it discards the message. If
> that happens and either the mandatory or immediate flag were set, and
> the message could not be routed to any other queues / consumers, then
> the message is returned to the sender with basic.return.
>
> We can think of other actions to take instead of discarding messages,
> but the above is simple and neatly exploits the existing
> mandatory/immediate functionality.

I think this is a good idea of how to use the mangement functionality
that comes with OTP. This is one of the reasons why we are using OTP
in the first place.

Ben