Re: block-level incremental backup

On Tue, Sep 3, 2019 at 12:46 PM Ibrar Ahmed <ibrar(dot)ahmad(at)gmail(dot)com> wrote:
> I did that and have experience working on the TAR format. I was curious about what
> "best/newest" you are talking.

Well, why not go look it up?

On my MacBook, tar is documented to understand three different tar
formats: gnutar, ustar, and v7, and two sets of extensions to the tar
format: numeric extensions required by POSIX, and Solaris extensions.
It also understands the pax and restricted-pax formats which are
derived from the ustar format. I don't know what your system
supports, but it's probably not hugely different; the fact that there
are multiple tar formats has been documented in the tar man page on
every machine I've checked for the past 20 years. Here, 'man tar'
refers the reader to 'man libarchive-formats', which contains the
details mentioned above.

A quick Google search for 'multiple tar formats' also finds
https://en.wikipedia.org/wiki/Tar_(computing)#File_format and
https://www.gnu.org/software/tar/manual/html_chapter/tar_8.html each
of which explains a good deal of the complexity in this area.

I don't really understand why I have to explain to you what I mean
when I say there are multiple tar formats when you can look it up on
Google and find that there are multiple tar formats. Again, the point
is that the current code only generates tar archives and therefore
only needs to generate one format, but if we add code that reads a tar
archive, it probably needs to read several formats, because there are
several formats that are popular enough to be widely-supported.

It's possible that somebody else here knows more about this topic and
could make better judgements than I can, but my view at present is
that if we want to read tar archives, we probably would want to do it
by depending on libarchive. And I don't think we should do that for
this project because I don't think it would provide much value.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company