[tor-relays] High processor usage - just curious

[teor]

> On 5 Feb 2018, at 23:21, Gary Smith <jaffacakemonster53 at gmail.com> wrote:
> 
> Hi,
> 
> I have noticed that after a few minutes of becoming online, and randomly perhaps a couple of times every hour (??) tor uses 100 % processor on all cores for about 40/50 seconds.
> 
> I am curious what is tor doing internally to need so much power? There is normally isn't more than 4 mbits going through my relay, I noticed this a while back on htop before the December load increase and on previous versions so this has got to be an "internal thing". There is no log entry when this happens.
> 
> I do not think it is a bug I am just curious why it needs this much computational power, 

Every hour, Tor downloads directory documents, creates diffs to recent consensuses,
and compresses the documents (and diffs) using gzip, zstd, and lzma.

This reduces client directory bandwidth, but costs CPU, RAM, and disk space.

If anyone wants to disable directory document caching, they can set:
DirPort 0
DirCache 0

T