Re: BUG #12779: pg_dump -Fd doesn't care about -Z

Hi Cristopher.

On Tue, Feb 17, 2015 at 4:54 PM, Christoph Berg <cb@df7cb.de> wrote:

> Re: To pgsql-bugs@postgresql.org 2015-02-17 <
> 20150217153446.2590.24945@wrigleys.postgresql.org>
> > 1164  1.fd
> > 1164  9.fd
> >
> > 1488  1.fc
> > 1160  9.fc
>
> Re: Francisco Olarte 2015-02-17 <CA+bJJbza-+UOuofSVCoHdn6kMa3u4zWzgKZhyU=
=3D
> Qab46R4vY-w@mail.gmail.com>
> > > pg_dump -Fd doesn't seem to care about -Z for Z > 0:
> > >
> >
> > With such a small dump, are you sure du's block granularity is not
> masking
> > the differences in -Fd ? ( Have you tried  du -b, or just comparing eve=
ry
> > size ?) ( In -Fc it is a single file, harder to mask ).
>
> I noticed when trying to compress an assumed-to-be-Z4 file a bit more
> using -Z7. The directory was 241GB in both cases.
>

=E2=80=8BI understand, but how did you measure it? I mean, from this aserti=
on one
could be 240.01 and the other 241, and the differences you are quoting is
between a -Z4 and -Z7, not -Z1 and -Z9 as in the above quoted text. Because
if you used du -h it may well be masking it again. =E2=80=8BIt seems rather=
 strange
that it is processing -Z0 and -Z1 and masking the rest of them ( also, it
seems they use the same routines for both modes, but compressor, specially
in the hi-compression modes which use larger windows, are much better when
fed a large file ).


> And if you compare with -Fc, the difference is a lot more than a few
> FS blocks.
>

=E2=80=8BThat is what I was pointing. With -Fc you have a single file, so a=
nything
bigger than a block is going to show ( this seem maybe be extents, rather
than blocks ). With -Fd you need a difference bigger than a block in a
single file. With du -b you just need a byte of diff, so just testing it
with it ( or asserting you've done it, I'm not gonna doubt it ) will make
your point stand out more.

=E2=80=8B=E2=80=8BRegards.
    Francisco Olarte.