| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Martijn van Oosterhout <kleptog(at)svana(dot)org> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, depesz(at)depesz(dot)com, Brendan Jurd <direvus(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Our regex vs. POSIX on "longest match" |
| Date: | 2012-03-05 20:30:13 |
| Message-ID: | 8837.1330979413@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Martijn van Oosterhout <kleptog(at)svana(dot)org> writes:
> On the otherhand, I think requiring an "overall longest match" makes
> your implementation non-polynomial complexity.
Only if you don't know how to implement it -- a DFA-based implementation
doesn't have much trouble with this.
> [ equivalence of knapsack problem to regexes with bounded repetition ]
Interesting, but note that neither the POSIX spec nor our implementation
permit arbitrarily large repetition counts, so the theoretical
NP-completeness is only theoretical.
> The question is, what are users expecting of the PostgreSQL regex
> implementation?
I think a minimum expectation is that we adhere to the POSIX
specification.
regards, tom lane
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