zlib selection UI, compression levels, descriptions

[ThomasWaldmann]

I just noticed that the UI for it is missing, it just offers all the others.

Also, I am not quite sure about the UI texts for the compression methods, my idea is rather:

• lz4 (modern, super fast low compression)
• zstd (modern, wide range from very fast to very high compression)
• lzma (legacy, slower higher compression)
• zlib (legacy, faster lower compression)

[ThomasWaldmann]

hmm, it doesn't let the user select the compression level.

[m3nu]

To avoid having one more field, I just picked a few and set the compression level as well. Nobody complained so far. Of course there could also be a second dropdown to choose the level for each compression algo.

Suggestion to choose the compression algo:

        self.repoCompression.addItem(self.tr('LZ4 (modern, superfast low compression)'), 'lz4')
        self.repoCompression.addItem(self.tr('Zst (modern, fast medium compression)'), 'zstd')
        self.repoCompression.addItem(self.tr('LZMA (legacy, slower higher compression)'), 'lzma')
        self.repoCompression.addItem(self.tr('ZLib (legacy, faster lower compression)'), 'zlib')
        self.repoCompression.addItem(self.tr('No Compression (fastest)'), 'none')

I we want to add the compression level instead of providing 3-4 default settings of algo + level, I'd just mark it as "good first issue".

[ThomasWaldmann]

• Zstd
• do not advise (fastest) for no compression, it is often not true because lz4 saves more time than it needs (overall).
• some well-picked algo+level sounds fine

[m3nu]

some well-picked algo+level sounds fine

Then let's get to it. These are the available algos and standard levels:

• Zstd (modern, fast medium compression): zstd,3
• LZ4 (modern, superfast low compression): lz4
• LZMA (legacy, slower higher compression): lzma,6
• ZLib (legacy, faster lower compression): zlib,6
• No Compression: none

First suggestion of combos:

1. Highest compression, very slow: auto,lzma,6
2. High compression, slow: auto,zstd,8
3. Medium compression and speed (default): zstd,3
4. Low compression, very fast: lz4

I looked roughly at those tests: https://community.centminmod.com/threads/compression-comparison-benchmarks-zstd-vs-brotli-vs-pigz-vs-bzip2-vs-xz-etc.12764/

Thinking:

• LZMA has very good compression, but is very slow. So adding auto to make it bearable.
• ZStd is fairly fast even at higher levels. Added auto again to skip e.g. images and videos.
• Last 2 fast alround settings

[ThomasWaldmann]

reverse order from fast to slow. that also moves borg's default lz4 compression to top of the list.

[m3nu]

OK. Then this wording and order, so users know the algo used.

1. Low compression, very fast (LZ4): lz4 (selected by default)
2. Low compression, fast (ZLib): zlib,6
3. Medium compression and speed (ZStd): zstd,3
4. High compression, slow (ZStd): auto,zstd,8
5. Highest compression, very slow (LZMA): auto,lzma,6

[ThomasWaldmann]

Some users may have started their repo with zlib, so this should be offered also.

Also noting that this is not a 1-dimensional thing, although a list might make it look like that.
speed, compression, algo type/age, ...

[m3nu]

I know. One could write a master thesis about this topic. But many users will just want to pick something and forget about it.

(added ZLib above)

[fischer-felix]

Is there a way to specify a custom compression level for an algorithm (zstd in my case)?
I would like to compress more than just level 8, but afaik there is currently no way to set the level.

[real-yfprojects]

You can add the command line option -C of borg create in the LineEdit in the ScheduleTab to modify compression.