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RE: [issue] pmwebd graphite api performance issue

To: Ken McDonell <kenj@xxxxxxxxxxxxxxxx>, "Frank Ch. Eigler" <fche@xxxxxxxxxx>
Subject: RE: [issue] pmwebd graphite api performance issue
From: Aurelien Gonnay <aurelien.gonnay@xxxxxxxxx>
Date: Tue, 28 Jul 2015 08:34:37 +0000
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Thread-topic: [issue] pmwebd graphite api performance issue
Hi Frank,

Thanks for this prompt reply.
I'd be glad to test this, but unfortunately, git urls to sourceware are not 
accessible from my end (https is pretty restricted).
Any chance you'd have an alternative git repo via http / a repo on github ?
As a last resort, if you can attach to this mail a git patch with the parent 
sha1 that'd be great.
Sorry for the inconvenience,

AG

-----Original Message-----
From: Ken McDonell [mailto:kenj@xxxxxxxxxxxxxxxx] 
Sent: 28 July 2015 06:35
To: Frank Ch. Eigler
Cc: pcp@xxxxxxxxxxx; Aurelien Gonnay
Subject: Re: [issue] pmwebd graphite api performance issue

G'day Frank.

On 28/07/15 10:26, Frank Ch. Eigler wrote:
> ..
> That could work too, though doing it naively could involve O(#metrics**2)
> iteration, which could itself be heavy. ...

The old computational complexity meets reality trap ... not all 
operations have the same cost.

I'll wager that for any von Neumann machine with real values of #metrics 
(and #instances), an O(#metrics**2) times for loop with simple test 
(p->indom == indom_of_interest && p->done == 0) will beat the pants off 
any O(#metrics) times loop with pmGetInDomArchive() + free()

> ... Doing it the cache way in pmwebd
> turned out to be easy:

OK, sounds good.

Cheers, Ken.

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