[rabbitmq-discuss] Memory High Watermark.

Chris Nicel Chris.Nicel at 15below.com
Wed Oct 16 16:29:45 BST 2013

Hi Simon/Duncan,

Thanks for your feedback. Useful information.



-----Original Message-----
From: Simon MacMullen [mailto:simon at rabbitmq.com]
Sent: 16 October 2013 16:01
To: Discussions about RabbitMQ
Cc: Chris Nicel
Subject: Re: [rabbitmq-discuss] Memory High Watermark.

On 16/10/13 15:43, Chris Nicel wrote:
> I would like to know more about the decision to default the memory
> high watermark to 40% of the installed RAM. Is this designed for use
> on a server with contended resources? If the server is dedicated to
> running RabbitMQ can this be raised to say 80% or 90% safely?

The original reason was a fear that although Erlang has per-process GC, we could theoretically end up in a situation where one process filled most of the VM, and the extra space required to GC it caused the machine to run out of space altogether.

That's quite unlikely though, the typical case is likely to be a VM with no one process dominating.

There's a second reason which I find more compelling: the high watermark is the point at which the broker stops accepting new messages, not the point at which it stops consuming more memory. In theory the one controls the other, but in practice there's likely to be some hysteresis.

We can't assume that swap space exists either, we have to assume that if we run out of memory then that's game over. If like almost everybody you do have swap space working then you can probably raise the limit somewhat. Personally I would be comfortable at 60 or 70%.

Cheers, Simon

Simon MacMullen
RabbitMQ, Pivotal

 15below Limited: Company registered in England and Wales No 3945289
Registered Office: Lyndean House, 43-46 Queens Road, Brighton BN1 3XB, United Kingdom

15below Australia Pty Limited: ABN 25 132 716 379
Level 21, Tower 2 Darling Park, 201 Sussex Street, Sydney, NSW 2000, Australia

Please think about the environment before printing this email.

This email and any attachments may be confidential and/or legally privileged and are solely for the use of the intended recipient.  If you have received this email in error please contact the sender.  Any views or opinions expressed within this e-mail are solely those of the sender, and do not necessarily represent those of 15below unless otherwise specifically stated.  Although 15below has taken every reasonable precaution to ensure that any attachment to this e-mail has been checked for viruses, it is strongly recommended that you carry out your own virus check before opening any attachment, as we cannot accept liability for any damage sustained as a result of software virus infection.

More information about the rabbitmq-discuss mailing list