Re: Processing a big file using more CPUs

[Shlomi Fish]

On Mon, 11 Feb 2019 23:54:43 +0100
Ole Tange <ole@tange.dk> wrote:

> On Mon, Feb 4, 2019 at 10:19 PM Nio Wiklund <nio.wiklund@gmail.com> wrote:
> :
> >    cat bigfile | parallel --pipe --recend '' -k gzip -9 > bigfile.gz  
> :
> > The reason why I want this is that I often create compressed images of
> > the content of a drive, /dev/sdx, and I lose approximately half the
> > compression improvement from gzip to xz, when using parallel. The
> > improvement in speed is good, 2.5 times, but I think larger blocks would
> > give xz a chance to get a compression much closer to what it can get
> > without parallel.
> >
> > Is it possible with with the current code? In that case how?  
> 
> Since version 2016-07-22:
> 
> parallel --pipepart -a bigfile --recend '' -k --block -1 xz > bigfile.xz
> parallel --pipepart -a /dev/sdx --recend '' -k --block -1 xz > bigfile.xz
> 
> Unfortunately the size computation of block devices only works under
> GNU/Linux.
> 
> (That said: pxz exists, and it may be more relevant to use here).
> 

Hi Ole!

https://jnovy.fedorapeople.org/pxz/node2.html - I see, but note that xz has a
-T flag now as well - https://linux.die.net/man/1/xz .

> 
> /Ole
> 



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