On Fri, Jan 15, 2016 at 4:39 PM, Benedikt Grundmann < bgrundm...@janestreet.com> wrote:
> > On Fri, Jan 15, 2016 at 4:26 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: > >> Kevin Grittner <kgri...@gmail.com> writes: >> > On Fri, Jan 15, 2016 at 9:33 AM, Tom Lane <t...@sss.pgh.pa.us> wrote: >> >> (FWIW, I think you probably wanted ,+ not ,* in the regex, else there's >> >> practically no constraint there, leading to having to consider O(N^2) >> >> or more possibilities.) >> >> > On master (commit cf7dfbf2) it responds to pg_cancel_backend(), >> > but it seems to be in an endless loop until you do that. >> >> A bit of further experimentation suggests the runtime growth is actually >> more like O(2^N). It will terminate in a reasonable amount of time if the >> input string is about half as long as the given example. >> >> The problem is that so far as the DFA engine is concerned, the pattern >> substring '(,*\1)+' can match almost anything at all, because it's >> equivalent to '(,*[^,]+)+' which is easily seen to match any string >> whatever that's got at least one non-comma. So, for each possible match >> to the substring '([^,]+)', of which there are lots, it has to consider >> every possible way of breaking up all the rest of the string into one or >> more substrings. The vast majority of those ways will fail when the >> backref match is checked, but there's no way to realize it before that. >> >> To be clear I'm perfectly happy with that query taking forever (I didn't > write it ;-)). The only thing I was unhappy about was that > pg_cancel/terminate_backend didn't work. If that is fixed great. > > >> regards, tom lane >> > > Hmm I just wanted to get the rpm for the latest 9.2 release for centos6 but it looks like you haven't released at least the link on this page for 9.2 http://yum.postgresql.org/repopackages.php says 7 in the filename which is certainly not 14 ;-) http://yum.postgresql.org/9.2/redhat/rhel-6-x86_64/pgdg-centos92-9.2-7.noarch.rpm Is that expected? Thanks, Bene
