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Date:      Mon, 8 Oct 2012 11:38:14 +0300
From:      Peter Pentchev <roam@ringlet.net>
To:        Wojciech Puchar <wojtek@wojtek.tensor.gdynia.pl>
Cc:        Brandon Falk <bfalk_bsd@brandonfa.lk>, freebsd-hackers@freebsd.org
Subject:   Re: SMP Version of tar
Message-ID:  <20121008083814.GA5830@straylight.m.ringlet.net>
In-Reply-To: <alpine.BSF.2.00.1210080838170.3664@wojtek.tensor.gdynia.pl>
References:  <5069C9FC.6020400@brandonfa.lk> <alpine.BSF.2.00.1210071859430.15957@wojtek.tensor.gdynia.pl> <324B736D-8961-4E44-A212-2ECF3E60F2A0@kientzle.com> <alpine.BSF.2.00.1210080838170.3664@wojtek.tensor.gdynia.pl>

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On Mon, Oct 08, 2012 at 08:38:33AM +0200, Wojciech Puchar wrote:
> >>gzip cannot - it is single stream.
> >
> >gunzip commutes with cat, so gzip
> >compression can be multi-threaded
> >by compressing separate blocks and
> >concatenating the result.
>=20
> right. but resulting file format must be different.

Not necessarily.  If I understand correctly what Tim means, he's talking
about an in-memory compression of several blocks by several separate
threads, and then - after all the threads have compressed their
respective blocks - writing out the result to the output file in order.
Of course, this would incur a small penalty in that the dictionary would
not be reused between blocks, but it might still be worth it.

G'luck,
Peter

--=20
Peter Pentchev	roam@ringlet.net roam@FreeBSD.org peter@packetscale.com
PGP key:	http://people.FreeBSD.org/~roam/roam.key.asc
Key fingerprint	FDBA FD79 C26F 3C51 C95E  DF9E ED18 B68D 1619 4553
Hey, out there - is it *you* reading me, or is it someone else?

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