Re: Oracle strace output - detail
- From: Martijn Bos <maboc@xxxxxxxx>
- To: Herring Dave - dherri <Dave.Herring@xxxxxxxxxx>
- Date: Fri, 13 Jan 2012 07:29:35 +0100
Hi,
On Thu, Jan 12, 2012 at 11:11:22PM +0000, Herring Dave - dherri wrote:
> Thanks for the additions, Phil. Do you have rules to follow for making
> REGEXP_* matches optimal? That kind of information is what I was looking
> for. I don't claim detailed knowledge of regular expression workings, so
> perhaps you could explain why:
>
> regexp_like(index_name,'^.*(COL)+.*$')
This regexp has a begin (^) and an end ($) tag. So the regexp library has a lot
information where (and how) to look. Always start at the first character and
end on the last one. The second regexp_like can start and end everywhere in the
string.
>
> ... is 7 to 8 times faster than:
>
> regexp_like(index_name,'.*COL.*')
>
> Is it because without a beginning-of-line anchor the parser doesn't know
> where to start searching for the pattern, so possibly it acts "greedy"
> whereas by default I believe REGEXP_* functions in Oracle are "lazy"?
hmmm...you have the same opinion allready :-)
Best Regards,
Martijn Bos
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