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GitLab is used only for code review, issue tracking and project management. Canonical locations for source code are still https://gitweb.torproject.org/ https://git.torproject.org/ and git-rw.torproject.org.

  • The Tor Project
  • Core
  • Tor
  • Issues
  • #40301

Closed
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Created Feb 18, 2021 by David Goulet@dgoulet😈Owner

relay: Reduce compression level when streaming

Turns out that most of the time, relays will stream back directory content on the highest compression level which means a lot of CPU for the best compression ratio.

However, in the case of authorities, when under DDoS from clients fetching non stop directory documents, it leads to a gigantic amount of CPU time being used on compressing requests that can not be pre-compresssed.

We propose to reduce the compression level, in case of streaming, to the lowest level. Considering that authorities, using Zstd, will see a significant reduction in CPU time but also will still gain on using the highest compression level that Zlib offers.

See https://docs.google.com/spreadsheets/d/1devQlUOzMPStqUl9mPawFWP99xSsRM8xWv7DNcqjFdo/edit#gid=0

Pre-compressed data will still use the current values, only streaming data will be downgraded to lowest ratio.

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Tor: 0.4.5.7-stable
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Tor: 0.4.5.7-stable (Past due)
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