[pacman-dev] backends

Jürgen Hötzel juergen at hoetzel.info
Thu Oct 26 17:29:15 EDT 2006

On Fri, Oct 27, 2006 at 12:03:40AM +0300, Roman Kyrylych wrote:
> 2006/10/26, Aaron Griffin <aaronmgriffin at gmail.com>:
> > What I'm saying is that you have the overhead of a full-scale database
> > with little gain.  Indexing by package names, yes that's great and
> > all, but that doesn't help with the slowest-of-the-slow -Ss operation.
> >  -Ss searches package names AND descriptions, allowing for regex
> > matching.  Sqlite (and most DBs) do not support regex matching.
> > Indexing the search by package name means little, because a -Ss "foo"
> > still SHOULD match a package named "barfoo" and a package with "foo"
> > in the description.  This means a sequential search.  Not only that,
> > but because the DB will not support regex, that means that one must
> > iterate over each and every entry, get the values at the C level,
> > apply a regex pattern, and note if it is a match or not.  The only
> > speed you gain would be in the initial opening of the files.  To me,
> > this does not mean a DB backend is the solution.  It may be better
> > than the files backend, yes, but not the best, and outperforming the
> > files backend is not hard... I was able to improve performance
> > approximately 6 times by simply using the db.tar.gz files in place of
> > disparate text files.
> Yes, the main problem with files backend is that huge amount of files
> in /var/lib/pacman that leads to slow performance on many filesystems.
> gdbm/sqlite/whatever has a big "+" that everithing can be in one file.

This is a big "-", because unix lovers prefer multiple text files. This
makes it easy to use powerful text/file-processing tools like "sed",
"awk", "shell" and "find" to build package-management related scripts.

> Plus, as I said, with SQLite you have the ability to easily use
> in-memory database + you have easy ACID transactions support. This
> will be faster than seeking through the /var/lib/pacman/ anyway. And
> there will be no need for pacman-optimize-like scripts for database
> backends.
> The overhead is not big. (A quote from sqlite.org: "Small code
> footprint: less than 250KiB fully configured or less than 150KiB with
> optional features omitted")

You will gain little performance (some seconds on a slow system?) at the
expense of complexity.

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