[Bug 254763] grep very slow with 13.0-RC4

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=254763

--- Comment #4 from parv <parv.0zero9+freebsd at gmail.com> ---
(In reply to Mark Millard from comment #2)

(A tolerable search would finish within ~1-2 second.)

Re: caching of file resulting in faster search ...
I created a 12 GB file filled with 0; searched for single letter via fgrep;
caused swap to increase to ~1 GB (swap size is 8 GB); lots of crunchy noise
ensued.

When I had enough, I ran egrep sans -i option ...

  1.16 real  0.07 user  0.30 sys


... and result after loading RAM as mentioned above for "egrep -i" ...

  49.13 real  45.28 user  0.63 sys


Relative time difference between two type of searches is rather consistent.


There is ~4-5 second improvement (time result hover around 43-45 second) for
"egrep -i" if it is run just after "egrep" or "egrep -i".


FWIW, configuration here ...

  - FreeBSD 13-STABLE as guest of Windows 10 host in VirtualBox 5.2.44;
  - /src-build/ports/INDEX-13 file is on separate pool of ZFS than the pool of
/usr/bin/egrep;
  - file systems are file-backed, allocated as SATA disks;
  - real memory: 8663 MB, avail memory: 7809 MB (of 16 GB RAM);
  - 2 "CPU"s have been allocated of Intel i5 6300U (Thinkpad X260).

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