Re: Future of our regular expression code - Mailing list pgsql-hackers

Jay,<br /><br /> Good links, and I've also looked at a few others with benchmarks.  I believe most of the benchmarks
aredone before PCRE implemented jit.  I haven't found a benchmark with jit enabled, so I'm not sure if it will make a
difference. Also I'm not sure how accurately the benchmarks will show how they will perform in an RDBMS environment.
Theoptimizer probably is a very important variable in many complex queries.  I'm leaning towards trying to implement
RE2and PCRE and running some benchmarks to see which performs best.  <br /><br /> Also would it be possible to set a
sessionvariable (lets say  PGREGEXTYPE) and set it to ARE (current alg), RE2, or PCRE, that way users could choose
whichimplementation they want (unless we find a single implementation that beats the others in almost all categories)? 
Oris this a bad idea?<br /><br /> Just a thought.<br /><br /><br /><div class="gmail_quote">On Mon, Feb 20, 2012 at
12:09AM, Jay Levitt <span dir="ltr"><<a href="mailto:jay.levitt@gmail.com">jay.levitt@gmail.com</a>></span>
wrote:<br/><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div
class="im">StephenFrost wrote:<br /><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc
solid;padding-left:1ex">Alright, I'll bite..  Which existing regexp implementation that's well<br /> written, well
maintained,and which is well protected against malicious<br /> regexes should we be considering then?<br
/></blockquote><br/></div> FWIW, there's a benchmark here that compares a number of regexp engines, including PCRE, TRE
andRuss Cox's RE2:<br /><br /><a href="http://lh3lh3.users.sourceforge.net/reb.shtml"
target="_blank">http://lh3lh3.users.<u></u>sourceforge.net/reb.shtml</a><br/><br /> The fastest backtracking-style
engineseems to be oniguruma, which is native to Ruby 1.9 and thus not only supports Unicode but I'd bet performs pretty
wellon it, on account of it's developed in Japan.  But it goes pathological on regexen containing '|'; the only safe
choiceamong PCRE-style engines is RE2, but of course that doesn't support backreferences.<br /><br /> Russ's page on
re2(<a href="http://code.google.com/p/re2/" target="_blank">http://code.google.com/p/re2/</a><u></u>) says:<br /><br />
"Ifyou absolutely need backreferences and generalized assertions, then RE2 is not for you, but you might be interested
inirregexp, Google Chrome's regular expression engine."<br /><br /> That's here:<br /><br /><a
href="http://blog.chromium.org/2009/02/irregexp-google-chromes-new-regexp.html"
target="_blank">http://blog.chromium.org/2009/<u></u>02/irregexp-google-chromes-<u></u>new-regexp.html</a><br/><br />
Sadly,it's in Javascript.  Seems like if you need a safe, performant regexp implementation, your choice is (a) finish
PLv8and support it on all platforms, or (b) add backreferences to RE2 and precompile it to C with Comeau (if that's
stillaround), or...<span class="HOEnZb"><font color="#888888"><br /><br /> Jay</font></span><div class="HOEnZb"><div
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