Re: [HACKERS] Future of our regular expression code
On Sat, Feb 18, 2012 at 21:16, Vik Reykja vikrey...@gmail.com wrote: I would be willing to have a go at translating test cases. I do not (yet) have the C knowledge to maintain the regex code, though. I got suddenly swamped and forgot I had signed up for this. I'm still pretty swamped and I would like these regression tests to be in for 9.2 so if someone else would like to pick them up, I would be grateful. If they're still not done by the time I resurface, I will attack them again.
Re: [HACKERS] Future of our regular expression code
Vik Reykja vikrey...@gmail.com writes: On Sat, Feb 18, 2012 at 21:16, Vik Reykja vikrey...@gmail.com wrote: I would be willing to have a go at translating test cases. I do not (yet) have the C knowledge to maintain the regex code, though. I got suddenly swamped and forgot I had signed up for this. I'm still pretty swamped and I would like these regression tests to be in for 9.2 so if someone else would like to pick them up, I would be grateful. FWIW, I spent a few minutes looking at the Tcl regression tests and realized that they are not in a form that's tremendously useful to us. What they are, unsurprisingly, are Tcl scripts, and a lot of the specific test cases are couched as calls to special-purpose Tcl functions. I tried inserting some hooks that would print out the arguments/results of the underlying regexp and regsub calls, but didn't get far (my Tcl is way too rusty :-(). I also found that quite a few of the test cases are concerned with features that are not accessible, or at least not accessible in the same way, from our SQL functions. Those test cases would still be worthwhile for a standalone library package, but they won't be much use in a Postgres regression test. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Future of our regular expression code
Jay, Good links, and I've also looked at a few others with benchmarks. I believe most of the benchmarks are done 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. The optimizer probably is a very important variable in many complex queries. I'm leaning towards trying to implement RE2 and PCRE and running some benchmarks to see which performs best. Also would it be possible to set a session variable (lets say PGREGEXTYPE) and set it to ARE (current alg), RE2, or PCRE, that way users could choose which implementation they want (unless we find a single implementation that beats the others in almost all categories)? Or is this a bad idea? Just a thought. On Mon, Feb 20, 2012 at 12:09 AM, Jay Levitt jay.lev...@gmail.com wrote: Stephen Frost wrote: Alright, I'll bite.. Which existing regexp implementation that's well written, well maintained, and which is well protected against malicious regexes should we be considering then? FWIW, there's a benchmark here that compares a number of regexp engines, including PCRE, TRE and Russ Cox's RE2: http://lh3lh3.users.**sourceforge.net/reb.shtmlhttp://lh3lh3.users.sourceforge.net/reb.shtml The fastest backtracking-style engine seems to be oniguruma, which is native to Ruby 1.9 and thus not only supports Unicode but I'd bet performs pretty well on it, on account of it's developed in Japan. But it goes pathological on regexen containing '|'; the only safe choice among PCRE-style engines is RE2, but of course that doesn't support backreferences. Russ's page on re2 (http://code.google.com/p/re2/**) says: If you absolutely need backreferences and generalized assertions, then RE2 is not for you, but you might be interested in irregexp, Google Chrome's regular expression engine. That's here: http://blog.chromium.org/2009/**02/irregexp-google-chromes-** new-regexp.htmlhttp://blog.chromium.org/2009/02/irregexp-google-chromes-new-regexp.html Sadly, it's in Javascript. Seems like if you need a safe, performant regexp implementation, your choice is (a) finish PLv8 and support it on all platforms, or (b) add backreferences to RE2 and precompile it to C with Comeau (if that's still around), or... Jay -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/**mailpref/pgsql-hackershttp://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Future of our regular expression code
Billy Earney billy.ear...@gmail.com writes: Also would it be possible to set a session variable (lets say PGREGEXTYPE) and set it to ARE (current alg), RE2, or PCRE, that way users could choose which implementation they want (unless we find a single implementation that beats the others in almost all categories)? Or is this a bad idea? We used to have a GUC that selected the default mode for Spencer's package (ARE, ERE, or BRE), and eventually gave it up on the grounds that it did more harm than good. In particular, you really cannot treat the regex operators as immutable if their behavior varies depending on a GUC, which is more or less fatal from an optimization standpoint. So I'd say a GUC that switches engines, and thereby brings in subtler but no less real incompatibilities than the old one did, would be a pretty bad idea. Also, TBH I have exactly zero interest in supporting pluggable regex engines in Postgres. Regex is not sufficiently central to what we do to justify the work of coping with N different APIs and sets of idiosyncrasies. (Perl evidently sees that differently, and with some reason.) regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Future of our regular expression code
Tom, Thanks for your reply. So is the group leaning towards just maintaining the current regex code base, or looking into introducing a new library (RE2, PCRE, etc)? Or is this still open for discussion? Thanks! Billy On Mon, Feb 20, 2012 at 3:35 PM, Tom Lane t...@sss.pgh.pa.us wrote: Billy Earney billy.ear...@gmail.com writes: Also would it be possible to set a session variable (lets say PGREGEXTYPE) and set it to ARE (current alg), RE2, or PCRE, that way users could choose which implementation they want (unless we find a single implementation that beats the others in almost all categories)? Or is this a bad idea? We used to have a GUC that selected the default mode for Spencer's package (ARE, ERE, or BRE), and eventually gave it up on the grounds that it did more harm than good. In particular, you really cannot treat the regex operators as immutable if their behavior varies depending on a GUC, which is more or less fatal from an optimization standpoint. So I'd say a GUC that switches engines, and thereby brings in subtler but no less real incompatibilities than the old one did, would be a pretty bad idea. Also, TBH I have exactly zero interest in supporting pluggable regex engines in Postgres. Regex is not sufficiently central to what we do to justify the work of coping with N different APIs and sets of idiosyncrasies. (Perl evidently sees that differently, and with some reason.) regards, tom lane
Re: [HACKERS] Future of our regular expression code
Billy Earney billy.ear...@gmail.com writes: Thanks for your reply. So is the group leaning towards just maintaining the current regex code base, or looking into introducing a new library (RE2, PCRE, etc)? Or is this still open for discussion? Well, introducing a new library would create compatibility issues that we'd just as soon not deal with, so I think that that's only likely to be seriously entertained if we decide that Spencer's code is unmaintainable. That's not a foregone conclusion; IMO the only fact in evidence is that the Tcl community isn't getting it done. Since Brendan Jurd has volunteered to try to split that code out into a standalone library, I think such a decision really has to wait until we see if (a) he's successful and (b) the result attracts some kind of community around it. So in short, let's give him a couple years and then if things are no better we'll revisit this issue. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Future of our regular expression code
On 19 February 2012 15:49, Tom Lane t...@sss.pgh.pa.us wrote: That sounds great. BTW, if you don't have it already, I'd highly recommend getting a copy of Friedl's Mastering Regular Expressions. It's aimed at users not implementers, but there is a wealth of valuable context information in there, as well as a really good not-too-technical overview of typical implementation techniques for RE engines. You'd probably still want one of the more academic presentations such as the dragon book for reference, but I think Freidl's take on it is extremely useful. Thanks for the recommendations Tom. I've now got Friedl, and there's a dead-tree copy of 'Compilers' making its gradual way to me (no ebook). I've also been reading the article series by Russ Cox linked upthread -- it's good stuff. Are you far enough into the backrefs bug that you'd prefer to see it through, or would you like me to pick it up? Cheers, BJ -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Future of our regular expression code
Brendan Jurd dire...@gmail.com writes: Are you far enough into the backrefs bug that you'd prefer to see it through, or would you like me to pick it up? Actually, what I've been doing today is a brain dump. This code is never going to be maintainable by anybody except its original author without some internals documentation, so I've been trying to write some based on what I've managed to reverse-engineer so far. It's not very complete, but I do have some words about the DFA/NFA stuff, which I will probably revise and fill in some more as I work on the backref fix, because that's where that bug lives. I have also got a bunch of text about the colormap management code, which I think is interesting right now because that is what we are going to have to fix if we want decent performance for Unicode \w and related classes (cf the other current -hackers thread about regexes). I was hoping to prevail on you to pick that part up as your first project. I will commit what I've got in a few minutes --- look for src/backend/regex/README in that commit. I encourage you to add to that file as you figure stuff out. We could stand to upgrade a lot of the code comments too, of course, but I think a narrative description is pretty useful before diving into code. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Future of our regular expression code
On 20 February 2012 10:42, Tom Lane t...@sss.pgh.pa.us wrote: I have also got a bunch of text about the colormap management code, which I think is interesting right now because that is what we are going to have to fix if we want decent performance for Unicode \w and related classes (cf the other current -hackers thread about regexes). I was hoping to prevail on you to pick that part up as your first project. I will commit what I've got in a few minutes --- look for src/backend/regex/README in that commit. Okay, I've read through your README content, it was very helpful. I'll now go chew through some more reading material and then start studying our existing regex source code. Once I'm firing on all cylinders with this stuff, I'll begin to tackle the colormap. Cheers, BJ -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Future of our regular expression code
Tom, I did a google search, and found the following: http://www.arglist.com/regex/ Which states that Tcl uses the same library from Henry. Maybe someone involved with that project would help explain the library? Also I noticed at the url above is a few ports people did from Henry's code. I didn't download and analyze their code, but maybe they have made some comments that could help, or maybe have some improvements to the code.. Just a thought.. :) Billy Earney On Sun, Feb 19, 2012 at 5:42 PM, Tom Lane t...@sss.pgh.pa.us wrote: Brendan Jurd dire...@gmail.com writes: Are you far enough into the backrefs bug that you'd prefer to see it through, or would you like me to pick it up? Actually, what I've been doing today is a brain dump. This code is never going to be maintainable by anybody except its original author without some internals documentation, so I've been trying to write some based on what I've managed to reverse-engineer so far. It's not very complete, but I do have some words about the DFA/NFA stuff, which I will probably revise and fill in some more as I work on the backref fix, because that's where that bug lives. I have also got a bunch of text about the colormap management code, which I think is interesting right now because that is what we are going to have to fix if we want decent performance for Unicode \w and related classes (cf the other current -hackers thread about regexes). I was hoping to prevail on you to pick that part up as your first project. I will commit what I've got in a few minutes --- look for src/backend/regex/README in that commit. I encourage you to add to that file as you figure stuff out. We could stand to upgrade a lot of the code comments too, of course, but I think a narrative description is pretty useful before diving into code. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Future of our regular expression code
Billy Earney billy.ear...@gmail.com writes: I did a google search, and found the following: http://www.arglist.com/regex/ Hmm ... might be worth looking at those two pre-existing attempts at making a standalone library from Henry's code, just to see what choices they made. Which states that Tcl uses the same library from Henry. Maybe someone involved with that project would help explain the library? Um ... did you see the head message in this thread? regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Future of our regular expression code
Thanks Tom. I looked at the code in the libraries I referred to earlier, and it looks like the code in the regex directory is exactly the same as Walter Waldo's version, which has at least one comment from the middle of last decade (~ 2003). Has people thought about migrating to the pcre library? It seems to have a lot of neat features, and also has a jit, and it looks like it is being actively maintained and has decent comments. On Sun, Feb 19, 2012 at 7:40 PM, Tom Lane t...@sss.pgh.pa.us wrote: Billy Earney billy.ear...@gmail.com writes: I did a google search, and found the following: http://www.arglist.com/regex/ Hmm ... might be worth looking at those two pre-existing attempts at making a standalone library from Henry's code, just to see what choices they made. Which states that Tcl uses the same library from Henry. Maybe someone involved with that project would help explain the library? Um ... did you see the head message in this thread? regards, tom lane
Re: [HACKERS] Future of our regular expression code
Billy, * Billy Earney (billy.ear...@gmail.com) wrote: Thanks Tom. I looked at the code in the libraries I referred to earlier, and it looks like the code in the regex directory is exactly the same as Walter Waldo's version, which has at least one comment from the middle of last decade (~ 2003). Has people thought about migrating to the pcre library? It seems to have a lot of neat features, and also has a jit, and it looks like it is being actively maintained and has decent comments. It strikes me that you might benefit from reading the full thread. As Tom mentioned previously, pcre would require user-visible changes in behavior, including cases where things which work today wouldn't work. That requires a pretty high bar and I don't think we're anywhere near there with this. Thanks, Stephen signature.asc Description: Digital signature
Re: [HACKERS] Future of our regular expression code
On Sat, Feb 18, 2012 at 6:15 PM, Tom Lane t...@sss.pgh.pa.us wrote: A larger point is that it'd be a real shame for the Spencer regex engine to die off, because it is in fact one of the best pieces of regex technology on the planet. ... Another possible long-term answer is to finish the work Henry never did, that is make the code into a standalone library. That would make it available to more projects and perhaps attract other people to help maintain it. However, that looks like a lot of work too, with distant and uncertain payoff. I can't see how your first claim that the Spencer code is worth keeping around because it's just a superior regex implementation has much force unless we can accomplish the latter. If the library can be split off into a standalone library then it might have some longevity. But if we're the only ones maintaining it then it's just prolonging the inevitable. I can't see Postgres having its own special brand of regexes that nobody else uses being an acceptable situation forever. One thing that concerns me more and more is that most sufficiently powerful regex implementations are susceptible to DOS attacks. A database application is quite likely to allow users to decide directly or indirectly what regexes to apply and it can be hard to predict which regexes will cause which implementations to explode its cpu or memory requirements. We need a library that can be used to defend against malicious regexes and i suspect neither Perl's nor Python's library will suffice for this. -- greg -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Future of our regular expression code
Greg, * Greg Stark (st...@mit.edu) wrote: I can't see how your first claim that the Spencer code is worth keeping around because it's just a superior regex implementation has much force unless we can accomplish the latter. If the library can be split off into a standalone library then it might have some longevity. But if we're the only ones maintaining it then it's just prolonging the inevitable. I can't see Postgres having its own special brand of regexes that nobody else uses being an acceptable situation forever. One thing that concerns me more and more is that most sufficiently powerful regex implementations are susceptible to DOS attacks. A database application is quite likely to allow users to decide directly or indirectly what regexes to apply and it can be hard to predict which regexes will cause which implementations to explode its cpu or memory requirements. We need a library that can be used to defend against malicious regexes and i suspect neither Perl's nor Python's library will suffice for this. Alright, I'll bite.. Which existing regexp implementation that's well written, well maintained, and which is well protected against malicious regexes should we be considering then? While we might not be able to formalize the regex code as a stand-alone library, my bet would be that the Tcl folks (and anyone else using this code..) will be paying attention to the changes and improvments we're making. Sure, it'd be easier for them to incorporate those changes if they could just pull in a new version of the library, but we can't all have our cake and eat it too. Thanks, Stephen signature.asc Description: Digital signature
Re: [HACKERS] Future of our regular expression code
Greg Stark st...@mit.edu writes: ... We need a library that can be used to defend against malicious regexes and i suspect neither Perl's nor Python's library will suffice for this. Yeah. Did you read the Russ Cox papers referenced upthread? One of the things Google wanted was provably limited resource consumption, which motivated them going with a pure-DFA-no-exceptions implementation. However, they gave up backrefs to get that, which is probably a compromise we're not willing to make. One thing that's been bothering me for awhile is that we don't have any CHECK_FOR_INTERRUPTS or equivalent in the library's NFA search loops. It wouldn't be hard to add one but that'd be putting PG-specific code into the very heart of the library, which is something I've tried to resist. One of the issues we'll have to face if we do try to split it out as a standalone library is how that type of requirement can be met. (And, BTW, that's the kind of hack that we would probably not get to make at all with any other library, so the need for it is not evidence that getting away from Spencer's code would be a good thing.) regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Future of our regular expression code
On 02/19/2012 10:28 PM, Greg Stark wrote: One thing that concerns me more and more is that most sufficiently powerful regex implementations are susceptible to DOS attacks. There's a list of evil regexes at http://en.wikipedia.org/wiki/ReDoS The Perl community's reaction to Russ Cox's regex papers has some interesting comments along these lines too: http://www.perlmonks.org/?node_id=597262 That brings up the backreferences concerns Tom already mentioned. Someone also points out the Thompson NFA that Cox advocates in his first article can use an excessive amount of memory when processing Unicode: http://www.perlmonks.org/?node_id=597312 Aside--Cox's Regular Expression Matching with a Trigram Index is an interesting intro to trigram use for FTS purposes, and might have some inspirational ideas for further progress in that area: http://swtch.com/~rsc/regexp/regexp4.html -- Greg Smith 2ndQuadrant USg...@2ndquadrant.com Baltimore, MD PostgreSQL Training, Services, and 24x7 Support www.2ndQuadrant.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Future of our regular expression code
Stephen Frost wrote: Alright, I'll bite.. Which existing regexp implementation that's well written, well maintained, and which is well protected against malicious regexes should we be considering then? FWIW, there's a benchmark here that compares a number of regexp engines, including PCRE, TRE and Russ Cox's RE2: http://lh3lh3.users.sourceforge.net/reb.shtml The fastest backtracking-style engine seems to be oniguruma, which is native to Ruby 1.9 and thus not only supports Unicode but I'd bet performs pretty well on it, on account of it's developed in Japan. But it goes pathological on regexen containing '|'; the only safe choice among PCRE-style engines is RE2, but of course that doesn't support backreferences. Russ's page on re2 (http://code.google.com/p/re2/) says: If you absolutely need backreferences and generalized assertions, then RE2 is not for you, but you might be interested in irregexp, Google Chrome's regular expression engine. That's here: http://blog.chromium.org/2009/02/irregexp-google-chromes-new-regexp.html Sadly, it's in Javascript. Seems like if you need a safe, performant regexp implementation, your choice is (a) finish PLv8 and support it on all platforms, or (b) add backreferences to RE2 and precompile it to C with Comeau (if that's still around), or... Jay -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
[HACKERS] Future of our regular expression code
As those who've been paying attention to it know, our regular expression library is based on code originally developed by Henry Spencer and contributed by him to the Tcl project. We adopted it out of Tcl in 2003. Henry intended to package the code as a standalone library as well, but that never happened --- AFAICT, Henry dropped off the net around 2002, and I have no idea what happened to him. Since then, we've been acting as though the Tcl guys are upstream maintainers for the regex code, but in point of fact there does not appear to be anybody there with more than the first clue about that code. This was brought home to me a few days ago when I started talking to them about possible ways to fix the quantified-backrefs problem that depesz recently complained of (which turns out to have been an open bug in their tracker since 2005). As soon as I betrayed any indication of knowing the difference between a DFA and an NFA, they offered me commit privileges :-(. And they haven't fixed any other significant bugs in the engine in years, either. So I think it's time to face facts and accept that Tcl are not a useful upstream for the regex code. And we can't just let it sit quietly, because we have bugs to fix (at least the one) as well as enhancement requests such as the nearby discussion about recognizing high Unicode code points as letters. A radical response to this would be to drop the Spencer regex engine and use something else instead --- probably PCRE, because there are not all that many alternatives out there. I do not care much for this idea though. It would be a significant amount of work in itself, and there's no real guarantee that PCRE will continue to be maintained either, and there would be some user-visible compatibility issues because the regex flavor is a bit different. A larger point is that it'd be a real shame for the Spencer regex engine to die off, because it is in fact one of the best pieces of regex technology on the planet. See Jeffrey Friedl's Mastering Regular Expressions (O'Reilly) --- at least, that's what he thought in the 2002 edition I have, and it's unlikely that things have changed much. So I'm feeling that we gotta suck it up and start acting like we are the lead maintainers for this code, not just consumers. Another possible long-term answer is to finish the work Henry never did, that is make the code into a standalone library. That would make it available to more projects and perhaps attract other people to help maintain it. However, that looks like a lot of work too, with distant and uncertain payoff. Comments, other ideas? regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Future of our regular expression code
On Sat, Feb 18, 2012 at 6:15 PM, Tom Lane t...@sss.pgh.pa.us wrote: So I'm feeling that we gotta suck it up and start acting like we are the lead maintainers for this code, not just consumers. By we, I take it you mean you personally? There are many requests I might make for allocations of your time and that wouldn't even be a lower priority item on such a list. Of course, your time allocation is not my affair, so please take my words as a suggestion and a compliment. Do we have volunteers that might save Tom from taking on this task? It's not something that requires too much knowledge and experience of PostgreSQL, so is an easier task for a newcomer. -- Simon Riggs http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Future of our regular expression code
* Simon Riggs (si...@2ndquadrant.com) wrote: On Sat, Feb 18, 2012 at 6:15 PM, Tom Lane t...@sss.pgh.pa.us wrote: So I'm feeling that we gotta suck it up and start acting like we are the lead maintainers for this code, not just consumers. By we, I take it you mean you personally? I'm pretty sure he meant the PG project, and I'd agree with him- we're going to have to do it if no one else is. I suspect the Tcl folks will be happy to look at incorporating anything we fix, if they can, but it doesn't sound like they'll be able to help with fixing things much. Do we have volunteers that might save Tom from taking on this task? It's not something that requires too much knowledge and experience of PostgreSQL, so is an easier task for a newcomer. Sure, it doesn't require knowledge of PG, but I dare say there aren't very many newcomers who are going to walk in knowing how to manage complex regex code.. I haven't seen too many who can update gram.y, much less make our regex code handle Unicode better. I'm all for getting other people to help with the code, of course, but I wouldn't hold my breath and leave existing bugs open on the hopes that someone's gonna show up. Thanks, Stephen signature.asc Description: Digital signature
Re: [HACKERS] Future of our regular expression code
Stephen Frost sfr...@snowman.net writes: * Simon Riggs (si...@2ndquadrant.com) wrote: Do we have volunteers that might save Tom from taking on this task? It's not something that requires too much knowledge and experience of PostgreSQL, so is an easier task for a newcomer. Sure, it doesn't require knowledge of PG, but I dare say there aren't very many newcomers who are going to walk in knowing how to manage complex regex code.. I haven't seen too many who can update gram.y, much less make our regex code handle Unicode better. I'm all for getting other people to help with the code, of course, but I wouldn't hold my breath and leave existing bugs open on the hopes that someone's gonna show up. Yeah ... if you *don't* know the difference between a DFA and an NFA, you're likely to find yourself in over your head. Having said that, this is eminently learnable stuff and pretty self-contained, so somebody who had the time and interest could make themselves into an expert in a reasonable amount of time. I'm not really eager to become the project's regex guru, but only because I have ninety-nine other things to do not because I don't find it interesting. Right at the moment I'm probably far enough up the learning curve that I can fix the backref problem faster than anyone else, so I'm kind of inclined to go do that. But I'd be entirely happy to let someone else become the lead hacker in this area going forward. What we can't do is just pretend that it doesn't need attention. In the long run I do wish that Spencer's code would become a standalone package and have more users than just us and Tcl, but that is definitely work I don't have time for now. I think somebody would need to commit significant amounts of time over multiple years to give it any real hope of success. One immediate consequence of deciding that we are lead maintainers and not just consumers is that we should put in some regression tests, instead of taking the attitude that the Tcl guys are in charge of that. I have a head cold today and am not firing on enough cylinders to do anything actually complicated, so I was thinking of spending the afternoon transliterating the Tcl regex test cases into SQL as a starting point. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Future of our regular expression code
On Sat, Feb 18, 2012 at 7:52 PM, Tom Lane t...@sss.pgh.pa.us wrote: One immediate consequence of deciding that we are lead maintainers and not just consumers is that we should put in some regression tests, instead of taking the attitude that the Tcl guys are in charge of that. I have a head cold today and am not firing on enough cylinders to do anything actually complicated, so I was thinking of spending the afternoon transliterating the Tcl regex test cases into SQL as a starting point. Having just had that brand of virus, I'd skip it and take the time off, like I should have. Translating the test cases is a great way in for a volunteer, so please leave a few easy things to get people started on the road to maintaining that. -- Simon Riggs http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Future of our regular expression code
On Sat, Feb 18, 2012 at 21:04, Simon Riggs si...@2ndquadrant.com wrote: On Sat, Feb 18, 2012 at 7:52 PM, Tom Lane t...@sss.pgh.pa.us wrote: One immediate consequence of deciding that we are lead maintainers and not just consumers is that we should put in some regression tests, instead of taking the attitude that the Tcl guys are in charge of that. I have a head cold today and am not firing on enough cylinders to do anything actually complicated, so I was thinking of spending the afternoon transliterating the Tcl regex test cases into SQL as a starting point. Having just had that brand of virus, I'd skip it and take the time off, like I should have. Translating the test cases is a great way in for a volunteer, so please leave a few easy things to get people started on the road to maintaining that. I would be willing to have a go at translating test cases. I do not (yet) have the C knowledge to maintain the regex code, though.
Re: [HACKERS] Future of our regular expression code
On 02/18/2012 02:25 PM, Stephen Frost wrote: Do we have volunteers that might save Tom from taking on this task? It's not something that requires too much knowledge and experience of PostgreSQL, so is an easier task for a newcomer. Sure, it doesn't require knowledge of PG, but I dare say there aren't very many newcomers who are going to walk in knowing how to manage complex regex code.. I haven't seen too many who can update gram.y, much less make our regex code handle Unicode better. I'm all for getting other people to help with the code, of course, but I wouldn't hold my breath and leave existing bugs open on the hopes that someone's gonna show up. Indeed, the number of people in the community who can hit the ground running with this is probably vanishingly small, sadly. (I haven't touched any formal DFA/NFA code in a couple of decades.) cheers andrew -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Future of our regular expression code
Vik Reykja vikrey...@gmail.com writes: On Sat, Feb 18, 2012 at 21:04, Simon Riggs si...@2ndquadrant.com wrote: Translating the test cases is a great way in for a volunteer, so please leave a few easy things to get people started on the road to maintaining that. I would be willing to have a go at translating test cases. I do not (yet) have the C knowledge to maintain the regex code, though. Sure, have at it. I was thinking that we should make a new regex.sql test file for any cases that are locale-independent. If they have any that are dependent on recognizing non-ASCII characters as letters, we could perhaps drop those into collate.linux.utf8.sql --- note that we might need my draft patch from yesterday before anything outside the LATIN1 character set would pass. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Future of our regular expression code
Tom Lane t...@sss.pgh.pa.us writes: Yeah ... if you *don't* know the difference between a DFA and an NFA, you're likely to find yourself in over your head. Having said that, So, here's a paper I found very nice to get started into this subject: http://swtch.com/~rsc/regexp/regexp1.html If anyone's interested into becoming our PostgreSQL regexp hero and still needs a good kicker, I would recommend starting here :) I see this paper mention the regexp code from Plan9, which supports both UTF8 and other muti-byte encodings, and is released as a library under the MIT licence: http://swtch.com/plan9port/unix/ Regards, -- Dimitri Fontaine http://2ndQuadrant.fr PostgreSQL : Expertise, Formation et Support -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Future of our regular expression code
Dimitri Fontaine dimi...@2ndquadrant.fr writes: Tom Lane t...@sss.pgh.pa.us writes: Yeah ... if you *don't* know the difference between a DFA and an NFA, you're likely to find yourself in over your head. Having said that, So, here's a paper I found very nice to get started into this subject: http://swtch.com/~rsc/regexp/regexp1.html Yeah, I just found that this afternoon myself; it's a great intro. If you follow the whole sequence of papers (there are 4) you'll find out that this guy built a new regexp engine for Google, and these papers are basically introducing/defending its design. It turns out they've released it under a BSD-ish license, so for about half a minute I was thinking there might be a new contender for something we could adopt. But there turn out to be at least two killer reasons why we won't: * it's in C++ not C * it doesn't support backrefs, as well as a few other features that maybe aren't as interesting but still would represent compatibility gotchas if they went away. Too bad. But the papers are well worth reading. One thing I took away from them is that it's possible to do capturing parens, though not backrefs, without back-tracking. Spencer's code treats both of those features as messy (ie, slow, because they force use of the NFA-style backtracking search code). So there might be reason to reimplement the parens-but-no-backrefs case using some ideas from these papers. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Future of our regular expression code
On Sun, Feb 19, 2012 at 1:55 AM, Tom Lane t...@sss.pgh.pa.us wrote: Dimitri Fontaine dimi...@2ndquadrant.fr writes: Tom Lane t...@sss.pgh.pa.us writes: Yeah ... if you *don't* know the difference between a DFA and an NFA, you're likely to find yourself in over your head. Having said that, So, here's a paper I found very nice to get started into this subject: http://swtch.com/~rsc/regexp/regexp1.html Yeah, I just found that this afternoon myself; it's a great intro. If you follow the whole sequence of papers (there are 4) you'll find out that this guy built a new regexp engine for Google, and these papers are basically introducing/defending its design. It turns out they've released it under a BSD-ish license, so for about half a minute I was thinking there might be a new contender for something we could adopt. But there turn out to be at least two killer reasons why we won't: * it's in C++ not C * it doesn't support backrefs, as well as a few other features that maybe aren't as interesting but still would represent compatibility gotchas if they went away. Another interesting library, technology-wise, is libtre: http://laurikari.net/tre/about/ http://laurikari.net/tre/documentation/ NetBSD plans to replace the libc regex with it: http://netbsd-soc.sourceforge.net/projects/widechar-regex/ http://groups.google.com/group/muc.lists.netbsd.current-users/browse_thread/thread/db5628e2e8f810e5/a99c368a6d22b6f8?lnk=gstq=libtre#a99c368a6d22b6f8 Another useful project - ATT regex tests: http://www2.research.att.com/~gsf/testregex/ About our Spencer code - if we don't have resources (not called Tom) to clean it up and make available as library (in short term - at least to TCL folks) we should drop it. Because it means it's dead end, however good it is. -- marko -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Future of our regular expression code
On Sat, Feb 18, 2012 at 7:24 PM, Marko Kreen mark...@gmail.com wrote: About our Spencer code - if we don't have resources (not called Tom) Is there anything that would be worth talking about directly with Henry? He's in one of my circles of colleagues; had dinner with a group that included him on Thursday. -- When confronted by a difficult problem, solve it by reducing it to the question, How would the Lone Ranger handle this? -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Future of our regular expression code
Christopher Browne cbbro...@gmail.com writes: On Sat, Feb 18, 2012 at 7:24 PM, Marko Kreen mark...@gmail.com wrote: About our Spencer code - if we don't have resources (not called Tom) Is there anything that would be worth talking about directly with Henry? He's in one of my circles of colleagues; had dinner with a group that included him on Thursday. Really!? I had about come to the conclusion he was dead, because he's sure been damn invisible as far as I could find. Is he still interested in what happens with his regex code, or willing to answer questions about it? regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Future of our regular expression code
On 19 February 2012 06:52, Tom Lane t...@sss.pgh.pa.us wrote: Yeah ... if you *don't* know the difference between a DFA and an NFA, you're likely to find yourself in over your head. Having said that, this is eminently learnable stuff and pretty self-contained, so somebody who had the time and interest could make themselves into an expert in a reasonable amount of time. I find myself in possession of both time and interest. I have to admit up-front that I don't have experience with regex code, but I do have some experience with parsers generally, and I'd like to think some of that skillset would transfer to this problem. I also find regexes fascinating and extremely useful, so learning more about them will be no hardship. I'd happily cede to an expert, should one appear, but otherwise I'm all for moving the regex code into a discrete library, and I'm volunteering to take a swing at it. Cheers, BJ -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Future of our regular expression code
Brendan Jurd dire...@gmail.com writes: On 19 February 2012 06:52, Tom Lane t...@sss.pgh.pa.us wrote: Yeah ... if you *don't* know the difference between a DFA and an NFA, you're likely to find yourself in over your head. Having said that, this is eminently learnable stuff and pretty self-contained, so somebody who had the time and interest could make themselves into an expert in a reasonable amount of time. I find myself in possession of both time and interest. I have to admit up-front that I don't have experience with regex code, but I do have some experience with parsers generally, and I'd like to think some of that skillset would transfer to this problem. I also find regexes fascinating and extremely useful, so learning more about them will be no hardship. I'd happily cede to an expert, should one appear, but otherwise I'm all for moving the regex code into a discrete library, and I'm volunteering to take a swing at it. That sounds great. BTW, if you don't have it already, I'd highly recommend getting a copy of Friedl's Mastering Regular Expressions. It's aimed at users not implementers, but there is a wealth of valuable context information in there, as well as a really good not-too-technical overview of typical implementation techniques for RE engines. You'd probably still want one of the more academic presentations such as the dragon book for reference, but I think Freidl's take on it is extremely useful. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
