[tor-bugs] #24857 [Core Tor/Tor]: tor 0.3.1.9 100% cpu load

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#24857: tor 0.3.1.9 100% cpu load
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 Reporter:  Eugene646                            |          Owner:  (none)
     Type:  defect                               |         Status:  new
 Priority:  Medium                               |      Milestone:  Tor:
                                                 |  unspecified
Component:  Core Tor/Tor                         |        Version:  Tor:
                                                 |  0.3.1.9
 Severity:  Normal                               |     Resolution:
 Keywords:  cpu, windows, linux, performance,    |  Actual Points:
  regression, 033-triage-20180326,               |
  033-removed-20180326, 034-deferred-20180602,   |
  035-removed-20180711                           |
Parent ID:  #25500                               |         Points:
 Reviewer:                                       |        Sponsor:
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Comment (by mestriga):

 I have the same problem in my new relay (Tor 0.3.3.7 from the Windows
 Expert Bundle). CPU goes to 100% on each diff generation cycle for several
 minutes (sometimes more than 30 minutes), making the machine barely
 responsive.

 There is definitely a pattern to it. The problem starts once the number of
 files in the consensus cache directory ("./diff-cache") reaches 64 files
 (far less than needed to store 72 hours of diffs). CPU usage goes up when
 diff generation starts and when it goes down again, there are again 64
 files in the diff-cache directory. Looking at the contents of the
 consensus diffs stored there, there are gaps (some diffs missing for which
 older diffs are present). There is clearly something wrong with the code
 that manages the limit of files in the diff-cache folder.

 Setting MaxConsensusAgeForDiffs to 9 kept the number of files in the diff-
 cache directory under 64 and made the problem go away completely.
 Consensus diff generation now takes a few seconds.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/24857#comment:29>
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