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Re: [Cfengine-develop] caching checksums with cfservd

From: Mark . Burgess
Subject: Re: [Cfengine-develop] caching checksums with cfservd
Date: Thu, 12 Aug 2004 07:28:59 +0200 (MEST)

On 11 Aug, Luke A. Kanies wrote:
> Hi,
> I'm getting to the point where I'm doing a lot of data transfer with 
> cfservd, and I'd like to stop having cfservd force a checksum on every 
> file transfer (as seen in cfservd.c where ChecksumChanged is passed 'true' 
> as the value of 'refresh').
> Would there be some problem if I made this change?  I know that I would 
> need some kind of aging mechanism, but even if I could cache sums for five 
> minutes I would see a performance benefit, because I'm looking at having 
> hundreds of machines connect and get checksums for hundreds of files, 
> possible up to hundreds of MB of data, and in the space of about half an 
> hour.  If I could cache those sums, I would be much much much happier.
> Any idea how hard it would be to make this work?  Maybe force a stat if 
> we're running inside cfservd, and only force a sum if the stat shows a 
> difference?
> Luke

Luke. Originally the checksums were cached, as you observe in the variable
CHECKSUMUPDATES. I had tonnes of trouble with berkeley db on this
and got rid of it for stability. However, I always intended to come
back to it, but never have... so yes I would be very interested
in fixing this. Thanks for pointing it out.

Stating is, of course, a costly operation too for high performance.
It might be worthwhile having an optimizer that works like locks,
so that updates cannot happen more often than, say, once every half hour.

These things tend to get away from me.


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