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Re: LZ4 compression

From: Stefan Sperling <stsp_at_elego.de>
Date: Wed, 26 Jul 2017 12:09:26 +0200

On Mon, Jul 17, 2017 at 02:54:59PM +0200, Evgeny Kotkov wrote:
> https://svn.apache.org/r1801974 adds negotiation and support for LZ4 in
> mod_dav_svn and in ra_serf. Except for the PUT requests, which require a
> couple of tweaks to the negotiation scheme, with this change svndiff2 with
> LZ4 will be used in the repository on-disk data and as the wire format for
> http://, if the corresponding compression level is set to 1.
>
> Speaking of only using it with compression level 1, that's not a starting
> point. While LZ4 offers superior speeds, it is not a substitute for any
> zlib compression level > 1, including our current default of 5, as the
> latter gives better compression ratio.
>
> I was thinking that it might make sense to make the compression level 1 our
> new default, so that new installations would benefit from the increased
> speed, while still keeping a decent compression ratio. (If necessary, that
> could still be tweaked for better compression.)

I am not sure where we are at in the discussion of the new option knobs,
so I'll add my opinion here. Bear in mind I have not looked at the
implementation so I might have missed something. I'll just express
what I would like to see as somebody who occasionally has to debug
servers with plain config files and already has to deal with mountains
of existing config settings in Subversion and HTTPD.

FSFS8: Default to lz4.
       Allow use of zlib only with an option (+ compression-levels)
       or disallow zlib entirely with Format 8 and deprecate/ignore
       compression options in fsfs.conf.
       
RA protocols: Use client<->server negotiation for lz4; fallback to zlib
              Do not require me to set an option for this.
Received on 2017-07-26 12:09:41 CEST

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