Why does TeX Live "require" yearly updates?

Question

Every year TeX Live provides a new version. My recollection is that soon after a new version is released, the old version's tlmgr stops fetching updates to packages. They provide upgrading instructions with the disclaimer

This procedure is not bullet-proof, or especially recommended

There is no upgrade path for Windows. Looking at the release history, it is not clear to me what is actually changing between releases such that a full new install is required/recommended. I always thought of TeX Live as providing useful binaries (e.g., pdflatex, biber, and makeindex) and a convenient way of updating CTAN packages. What am I missing? Why does TeX Live need a new install every year?

Answer 1

Ok, here's an answer as the main developer of tlmgr and the whole TeX Live infrastructure. You have to decide two things:

• the freeze period before release of a new version
• upgradability from one release to the next

Concerning the former, freeze period: Normally during the year we do not make updates to the actual binaries, but only to scripts and the packaging. That means, that in preparation of a new release all the binaries have to be recompiled, which is a huge tasks and involved lots of time, and iterations. Bugs are fixed, code adapted so that it builds on all platforms (and there are many!). During this time we do not want to make partial upgrades of some binaries, because sometimes that needs to be accompanied with library file updates.

Another point is that during the freeze period critical new features are sometimes included in the texlive infrastructure and the tlmgr, which would be too dangerous to be released to the world in the normal course.

And finally, it is also about getting into a state that can be pressed onto DVD.

Now for the upgradability between releases: The reason in the first years were changes in the internals that did not allow upgrades (like format of the internal coding of options, etc.). This was in the first years (say 2008-2010) the most common reason. A normal upgrade was simply not trivially possible. Of course, one could write an upgrade script and make an NSIS installer for Windows, but we do not have time for that. We are volunteers and have to concentrate on the important things.

In the last years (say since 2010) there always was an upgrade procedure, although we normally didn't give it a lot of testing; that is the reason why we don't recommend it. Disk space is nowadays quite abundant, and having two installations in parallel is thus not such a pain. But still, there always was the way to upgrade.

On Windows this is unfortunately not so trivial, as the uninstaller and the registry etc etc is linked to release years, it is simply a pain on Windows, but that is a special case.

Finally, one more reason: In many cases in the last year, an update or a new installation would not have changed much in the amount of downloaded data, as often all the packages were updated in one way or the other (due to internal changes), which meant an upgrade would have involved downloading all packages, just like the installation.

I hope that all this makes our intention a bit more clear, and if there is anything unclear, or if someone has better ideas how to deal with it, we are open to suggestions!

Answer 2

I can't speak for TeX Live in particular, but I have been involved with Linux distributions from their very beginning, and I believe my observations there are relevant for TeX Live too (both are collections of disparate pieces that have to be selected, integrated and convinced to work nice together, each piece evolves at their own pace).

While in a perfect world such a software collection would be maintained forever, this isn't practical. New packages show up, old packages are overhauled, some packages are superseded by new ways of getting the work done. To maintain, say, TL-2011 would mean to keep "the old way" working, even if upstream has abandoned the package (or changed it so much that it isn't a drop-in replacement anymore). That means endless backporting and fixing old bugs. Volunteers for that are only found among dyed-in-the-wool masochists.

TeX Live maintenance requires knowledgeable people in a rather esoteric area, and those are in very short supply. Either they maintain 2011 forever (and no 2012, 2013, ...) or they concentrate on building and shipping the last version. Besides, working on shiny&new is always more fun, so there is more potential to attract new recruits there.

Perhaps they are enough to keep two versions reasonably up to date, but I guess not (as they have decided that they don't have the manpower, so mandatory yearly upgrade).

Answer 3

in addition to @vonbrand's excellent answer, one important reason to upgrade and "freeze" tex live annually is to provide a stable snapshot on physical media, largely for the benefit of members of the various user groups, but also for tex users who don't have convenient internet access.

this dvd (it no longer fits on a cd) is also physically packaged with some (la)tex-related books, particularly in germany; this (commercial) packaging is the reason why anything with a restrictive (non-free) license must be excluded from the collection.

Answer 4

To add some more information to the answers of @vonbrand and @barbara beeton:

One other reason is to change infrastructural things. Some time ago the tlmgr management tool was introduced with a graphical interface for (mainly) windows users. Also the package format was changed (I think it was from TL2008 to TL2009) from LZO to XZ which was not possible if not requesting a new installation as the whole infrastructure was changed.

But nevertheless it often is possible to update e.g. from TL2011 to TL2012 without any new full installation. But be careful: This is not supported by the developers and is not recommended! It works in some cases and in others not.

I have an hope that there will be kind of a rolling release scheme (as e.g. in Arch Linux or Gentoo), as this was a topic several times on TeX Live's mailing list.