[arch-general] Implement sql/sqlite database for pacman local database

[Alive 4ever]

On Fri, Oct 21, 2016 at 08:03:53PM +0200, Tinu Weber wrote:
> On Fri, Oct 21, 2016 at 17:20:53 +0000, Alive 4ever wrote:
> > [...] It seems that the local pacman databases are just subdirectories
> > with text files (desc, files) and gzipped text (mtree).
> > No wonder why local pacman databases tend to slow down over time and
> > need to be optimized periodically.
> This is a little contradictory: if it is just directories with text
> files (plain or compressed), how does it need "periodical optimisation"?
> What is optimised? And how?
Local text files uses the underlying filesystem capability to optimize.
Currently, pacman package includes a ``pacman-optimize`` script to do
manual periodic local database optimization.

Invoking ``pacman-optimize --help`` should give you a hint that pacman
developers recognize that there is a problem with many small files:
filesystem fragmentation.

Basically, the optimization is just file system rotation. The old
databases are archived into tar files in the tmp, the local database is
moved/renamed, the tar archive of local database is extracted back to its
original location. If everything goes fine, the renamed old database is
deleted.

> 
> > This would provide faster access for local database as sql databases
> > are optimized for fast access.
> This just adds complexity, and for what? Marginal performance gain (if
> at all? honestly, `pacman -Q` runs almost instantly here).

Filesystem fragmentation is no problem for faster disk.
> 
> Best,
> Tinu/ayekat