Value of memory

[Lightner, Jeff]

Also remember that "used" reported by "free" in Linux on the first line includes memory pre-allocated to cache and buffers that is readily usable on demand so isn't really allocated to specific processes like you'd see in a similarly configured UNIX system.   Be sure when trying to determine "used" that you're looking at the values on the second line instead as that shows what you have when buffers/cached are not included in the totals.



-----Original Message-----
From: bind-users-bounces at lists.isc.org [mailto:bind-users-bounces at lists.isc.org] On Behalf Of Fajar A. Nugraha
Sent: Thursday, August 07, 2014 12:07 AM
To: Robert Moskowitz
Cc: bind-users at isc.org
Subject: Re: Value of memory

On Thu, Aug 7, 2014 at 10:39 AM, Robert Moskowitz <rgm at htt-consult.com> wrote:
> I have a server that is only running bind 9.8.2 (Centos 6.5).  It has
> 2Gb memory and free reports ~1.7Gb used.
>
> I am looking at replacing this server with an armv7 board running
> Redsleeve (until Centos 7 is out and stable for armv7).  I have a
> choice of boards, one with 1Gb memory ($60) and one with 2Gb memory ($90).
>
> This server servers out my zones and supports the couple handfull of
> systems on my net.  I would like to eventually get to DNSSEC, but that
> is another stalled project.
>
> About the only meaningful difference between the two boards (btw,
> Cubieboard2 and Cubietruck) for my needs is the memory.  I know more
> memory is better, but how much better?
>
> Oh, why the move to arm?  Power consumption.  ROI for the C2 board is
> one year just on power saving.

It depends on how much load your server currently handle, and how your cache is configured.

I'd start with looking at your server load. Arm still have lower per-core performance compared to x86, so if you currently see high CPU utilization by named, I'd stick with x86.

Next see how your memory cache is configured. That should be where bind uses most memory. AFAIK by default max-cache-size is unlimited and max-cache-ttl is set to several days. See how much memory bind currently uses for cache, and then you can try configuring those two parameters (e.g. set an explicit max-cache-size to 512MB) and see how much memory bind (and the rest of the OS) uses then, and how well it performs. If it's still acceptable, then you can probably go with the 1GB board.

Cache can reduce the number of queries issued upstream and is very important on busy servers, but if you serve a relatively low number of queries from your clients then you won't see much difference between
(e.g.) 512MB and 1GB cache.

--
Fajar
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