Re: Pathological regexp match

2010/1/29 Alvaro Herrera <alvherre(at)commandprompt(dot)com>:
> Hi Michael,
>
> Michael Glaesemann wrote:
>> We came across a regexp that takes very much longer than expected.
>>
>> PostgreSQL 8.4.1 on x86_64-unknown-linux-gnu, compiled by GCC gcc (GCC) 4.1.2 20080704 (Red Hat 4.1.2-44), 64-bit
>>
>> SELECT 'ooo...' ~ $r$Z(Q)[^Q]*A.*?(\1)$r$; -- omitted for email brevity
>
> The ? after .* is pointless.  If you remove it, the query returns
> immediately.
>
> (There's a badly needed CHECK_FOR_INTERRUPTS in this code BTW)

Incidentally, I ran across the exact same issue with a non-greedy
regexp with a client earlier this week, and put on my TODO to figure
out a good place to stick a check for interrupts. Does this mean I
don't have to, because you're on it? ;)

--
Magnus Hagander
Me: http://www.hagander.net/
Work: http://www.redpill-linpro.com/