bug#22239: bug#21763: bug#22239: bug#22357: grep -f not only huge memory usage, but also huge time cost

[Norihiro Tanaka]

On Mon, 26 Dec 2016 12:07:49 -0800
Paul Eggert <address@hidden> wrote:

> Norihiro Tanaka wrote:
> > Hmm, how about the following test cases, although it is extreame?
> 
> I don't think we need to worry about performance for the case when -w
> is given, and a pattern matches data that contains non-word
> characters. In practice, such cases are rare. I expect that most
> users would be surprised that -w can match non-word characters, and
> that users wouldn't object to -w rejecting such matches (if this
> wouldn't hurt performance significantly).
> 
> While looking into this I did find a very small performance tweak for
> the test case, and installed the attached.

Thanks.

BTW, with multiple patterns in current master, former uses fgrep matcher,
and later users grep matcher.  I think that it is not reasonable.

  env LC_ALL=C grep -w -f pat inp

  env LC_ALL=C grep -F -w -f pat inp

So I wrote the patch to use fgrep matcher for both.

0001-grep-imorove-performance-with-multiple-patterns.patch
Description: Text document