[pacman-dev] patch] My speed improvement

[Nagy Gabor]

> Hi,
> 
> so this is a index for groupnames implemented by symlinks. How do you
> ensure the index is up2date? 

I implemented it yesterday, but you can imagine that only ~1 extra
symlink creation/remove is needed in case of _alpm_db_write and
_alpm_db_remove, so this doesn't count.
 
> This is only performant because there are few groupnames. How do you 
> want to index pkg names? You will get more files. File-io is already
> the performance limiting part of of the current backend.

Yes. I tested with the case, when all file is a group (I put all files
to fakegroup) and there is not much difference. Because: In the current
state you _must_ read the desc files and my solution does only
"ls" (yes, in this twice but this is even much faster). The only thing 
remained, that free_grpcache is used too often now (because its
creating is fast from groupcache) so it should be replaced with
remove_from_grpcache and add_pkg_in_grpcache.

> Jürgen

Other benefits:
1. groups are categorised now, so we can implement that load only
groupnames to grpcache and we fill in the package list on demand
2. you needn't load pkgcache if you do -Qg or -Sg

But this was only the first part of my ideas, I think .providers
and .conflicts will be effective (I plan store them in a "pkgcache").
Yes, this will be useful if few packages have CONFLICTS and PROVIDES
filled in, but this is always true I think.

Summary: I think we can skip "brute force scan" for providers, groups
and conflicts with this "dotdir way". One case, when you need to read
the whole database: -Ss and similars <- we should use the db.tar file
(which we store instead of delete after syncing) in these cases for
sync repos.

Nagy Gabor

P.S.: I'm not so enthusiastic now, because overall we can reduce
pacman's running time by about 50% only, because the ldconfig is really
slow and we must run it in case of most of the packages.