python-zstandard VS ratarmount

I'm working on file formats called tif file which are on average a gigabyte of size. A middle step is to compress those files and I looked it up and found this and tried to use it. But unfortunately, the size of the compressed file is barely 100MB less than the original one and it takes like 1.5 minutes to compress it. I'm reading the entire file in memory instead of streaming it but I don't really think that could result in compression size. I'm also using high enough level of compression(20 level) but it still won't give me good results.

This is basically the same reason why I started with ratarmount (https://github.com/mxmlnkn/ratarmount) but the focus was more on runtime performance and random access and as the name suggests it started out with access to recursive tar archives. The current version should also work for your use case with recursive zips.

As an added complication this would need to work under windows (i need onenote and that's win only :/ ) ; this alone makes the majority of solutions that i came up with impossible. One way could've been splitting the data onto various tar files and then mounting those with rartarmount but...linux only :( .

Pragzip actually decompress in parallel and also access at random. I did a Show HN here: https://news.ycombinator.com/item?id=32366959

indexed_gzip https://github.com/pauldmccarthy/indexed_gzip can also do random access but is not parallel.

Both have to do a linear scan first though. The implementations however can do the linear scan on-demand, i.e., they scan only as far as needed.

bzip2 works very well with this approach. xz only works with this approach when compressed with multiple blocks. Similar is true for zstd.

For zstd, there also exists a seekable variant, which stores the block index at the end as metadata to avoid the linear scan. indexed_zstd offers random access to those files https://github.com/martinellimarco/indexed_zstd

I wrote pragzip and also combined all of the other random access compression backends in ratarmount to offer random access to TAR files that is magnitudes faster than archivemount: https://github.com/mxmlnkn/ratarmount

Or via the experimental AppImage I created this week:

    wget -O ratarmount 'https://github.com/mxmlnkn/ratarmount/releases/download/v0.10.0/ratarmount-manylinux2014_x86_64.AppImage'

I've recently been looking into this same issue because I analyse a lot of data like sosreports or other tar/compressed data from customer systems. Currently I untar these onto my zfs filesystem which works out OK because it has zstd compression enabled but I end up decompressing and recompressing which is quite expensive as often the files are GBs or more compressed.

But I've started using a tool called "ratarmount" (https://github.com/mxmlnkn/ratarmount) which creates an index once (and something I could automate our upload system to generate in advance, but you can also just process it lcoally) and then lets you fuse mount the file. This works pretty great with the only exception that I can't create scratch files inside the directory layout which in the past I'd wanted to do.

I was surprised how hard a problem to solve it is to get a bundle file format that is indexable and compressed with a good and fast compression algorithm which mostly boils down to zstd at this point.

While it works quite well, especially with gzip and bzip2, sadly the zstd and xz (and some other compression formats) don't allow for decompressing only parts of a file by default, even though it's possible the default tools aren't doing it. The nitty gritty details are summarised here:

Well, you could try to skip extraction and access the tar archive using ratarmount, and stack overlayfs on top to allow writing, but that will have an impact on compilation time.