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Re: [tor-bugs] #2334 [Torouter]: Torouter breaks with large cached-descriptors[.new] files
#2334: Torouter breaks with large cached-descriptors[.new] files
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Reporter: karsten | Owner: ioerror
Type: defect | Status: new
Priority: blocker | Milestone:
Component: Torouter | Version: Tor: 0.2.1.26
Keywords: | Parent:
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Comment(by karsten):
Replying to [comment:2 karsten]:
> As a next step we should investigate how many descriptors we need to
cache as a bridge (or as a relay). We can probably throw out descriptors
more quickly.
>
> I'm going to set up a new directory mirror to a) take hourly snapshots
of the cached-descriptors* files and b) log the requested descriptor
digests (using log granularity of 15 minutes). With these data we can
answer 1) for what consensuses we're keeping descriptors and 2) which
consensuses clients use to decide which descriptors to download. Once we
know that clients don't download old descriptors, we can stop caching
them.
I ran a similar experiment to the one described above. I modified a
moderately fast directory mirror to log which descriptors are requested
and collected a few hours of those logs. But instead of hourly snapshots I
took the cached-descriptors* files of a relay that was running for a
couple of days. No reason to wait a couple of days if we can have results
right now.
See the attached graph descriptor-age-2011-01-03.png.
You'll see that 97.12% of requested, but only 19.61% of cached descriptors
were last referenced in a consensus at most 3 hours old. Also note that
15.21% of cached descriptors are not referenced in any consensus at all.
That means if we threw out all descriptors that are not referenced in one
of the last 3 consensuses, we wouldn't be able to answer 2.88% of the
requests, but would reduce the cached-descriptors* files to 1/5 of the
current size.
What about these 2.88% of requests? Can the requesting clients even make
use of descriptors of relays that are very likely not running anymore?
--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/2334#comment:3>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online
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