zfs, a directory that used to hold lot of files and listing pause

[Nicolas Gilles]

On Thu, Oct 20, 2016 at 3:47 PM, Eugene M. Zheganin <emz at norma.perm.ru> wrote:
> Hi.
>
> I have FreeBSD 10.2-STABLE r289293 (but I have observed this situation on
> different releases) and a zfs. I also have one directory that used to have a
> lot of (tens of thousands) files. I surely takes a lot of time to get a
> listing of it. But now I have 2 files and a couple of dozens directories in
> it (I sorted files into directories). Surprisingly, there's still a lag
> between "ls" and an output:
>
>
> ===Cut===
>
> # /usr/bin/time -h ls
> .recycle        2016-01         2016-04         2016-07 2016-10
> sort-files.sh
> 2014            2016-02         2016-05         2016-08 ktrace.out
> sort-months.sh
> 2015            2016-03         2016-06         2016-09 old
> sounds
>         5.75s real              0.00s user              0.02s sys

Looks like it's not taking up any processing time, so my guess is
the lag probably comes from stalled I/O ... bad disk?

Does a second "ls" immediately returned (ie. metadata has been
cached) ?

>
> ===Cut===
>
>
> I've seen this situation before, on other servers, so it's not the first
> time I encounter this. However, it's not 100% reproducible (I mean, if I
> fill the directory with dozens of thousands of files, I will not certainly
> get this lag after the deletion).
>
> Has anyone seen this and does anyone know how to resolve this ? It's not
> critical issue, but it makes thing uncomfortable here. One method I'm aware
> of: you can move the contents of this directory to some other place, then
> delete it and create again. But it's kind of a nasty workaround.
>
>
> Thanks.
>
> Eugene.
>
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