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pcwalton's profile
Patrick Walton
Patrick Walton
Patrick Walton
@pcwalton

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Patrick Walton

@pcwalton

Research engineer at Mozilla

San Francisco, CA
pcwalton.github.io
Joined November 2009

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    1. Patrick Walton‏ @pcwalton 1 Jan 2014
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      Controversial opinion time: The advantages of Thompson NFA regexes are just theoretical and not worth it. PCRE is faster in the real world.

      4 replies 3 retweets 3 likes
    2. Geoff Langdale‏ @geofflangdale 15 Jul 2019
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      Replying to @pcwalton

      It's pretty funny you post this just after Cloudflare inflicted a major outage on half the world due to a pathologically backtracking regex. This opinion is fractally wrong - wrong at every level of magnification. PCRE is slower than modern automata-based regular expressions...pic.twitter.com/f343vgGZgU

      1 reply 0 retweets 0 likes
    3. Geoff Langdale‏ @geofflangdale 15 Jul 2019
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      Replying to @geofflangdale @pcwalton

      in the extreme pathological case but also on average cases, as both determinization and bitwise implementations are way faster than backtracking. The advantage of PCRE and backtracking is expressiveness, not speed. I don't know whether you're trolling here or just woefully ...

      1 reply 0 retweets 0 likes
    4. Geoff Langdale‏ @geofflangdale 15 Jul 2019
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      Replying to @geofflangdale @pcwalton

      underinformed. You're also wrong elsewhere on the thread where you claim that you need to have user-provided regexes to find a regex DDoS. It was, historically, not hard to find rules in the VRT set or the public Snort set that could have handcrafted input that would ...

      1 reply 0 retweets 0 likes
    5. Geoff Langdale‏ @geofflangdale 15 Jul 2019
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      Replying to @geofflangdale @pcwalton

      case the system to time out. Back in 2008-2009 or so, we found a regex where every "<" added would double the processing time in the public Snort set. Best of all, those systems *failed open* if they timed out, so in theory, if you could get a threat through that has such a ...

      2 replies 0 retweets 0 likes
      Patrick Walton‏ @pcwalton 15 Jul 2019
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      Replying to @geofflangdale

      The post you’re responding to is from 2014. I readily admit that @burntsushi5’s Rust regex implementation proved me wrong.

      9:26 PM - 15 Jul 2019
      2 replies 0 retweets 0 likes
        1. New conversation
        2. Patrick Walton‏ @pcwalton 15 Jul 2019
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          Replying to @pcwalton @geofflangdale @burntsushi5

          Note that the context behind that post is from experience with SpiderMonkey’s JS regex implementation and in particular how it gets benchmarked. For JS regex benchmarks it is all about how quickly you can JIT the regex to something reasonable.

          1 reply 0 retweets 0 likes
        3. Geoff Langdale‏ @geofflangdale 15 Jul 2019
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          Replying to @pcwalton @burntsushi5

          If I was silly enough to return to the world of regex (having been - ahem - granted my freedom by Intel) I think working with something where speed of starting to match an entirely unknown regex is paramount would be interesting. The world of Hyperscan, particularly, assumes ...

          2 replies 0 retweets 0 likes
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        2. Geoff Langdale‏ @geofflangdale 15 Jul 2019
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          Replying to @pcwalton @burntsushi5

          Ha. Welp, my tweetstorm is misdirected then. Silly me. Although in 2014 we'd been in business since about 2008 *selling* that capability (not widely known) and @burntsushi5's implementation is hardly the first OSS proof point (Russ Cox's blog posts date from 2007 onwards).

          1 reply 0 retweets 0 likes
        3. Andrew Gallant‏ @burntsushi5 16 Jul 2019
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          Replying to @geofflangdale @pcwalton

          To be fair, PCRE2's *JIT* is still faster than Rust's regex library in several cases, and faster than RE2 in a lot more cases. Literal optimizations really help bring Rust above RE2, otherwise performance between the two is pretty similar. Hyperscan is a cut above the rest. :P

          1 reply 0 retweets 1 like
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