[rrd-developers] [rrd] Re: rrdcached performance with >200k nodes

[Florian Forster]

Hi,

On Wed, Jan 13, 2010 at 11:08:44AM +0100, Mirek Lauš wrote:
> 31,901,245,144  ???:strcmp'2 [/lib/libc.so.7]

there are only three places where “strcmp” is used:

 * When initializing the journaling code. Should be run at startup only.
 * When checking for permission. This is called at least as often as
   “strcasecmp”, so this is probably not the problem either.
 * When looking up a node in the balanced binary search tree. This is
   most likely the place where all those invocations come from.

I'd say, if looking up stuff from a balanced search tree is the most
time-consuming operation, all the rest is pretty awesome efficient.

> Write rate is very low, disk IO is almost zero.
> CPU load done by rrdcached gets very high (100-200%).

How exactly did you measure those numbers? Can you provide us with
absolute numbers, especially IO-operations per second? Disk throughput
is not a relevant measure because disk seeks are the limiting factor.

Are you sure the process is using the CPU for calculating stuff rather
than just waiting for IO? In a typical “the server is as busy as can be”
scenario you'd have 100% (times the thread count, the value specified
with `-t') percent CPU usage with ca. 10% system, 5% user and 85%
IO-wait.

By the way, the limiting factor is (or, should ideally be) physical
memory. How big is RRDCacheD's resident segment size (RSS)?

Regards,
—octo
-- 
Florian octo Forster
Hacker in training
GnuPG: 0x91523C3D
http://verplant.org/
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