speeding up portage’s metadata cache

Gentoo’s portage keeps metadata about installed ebuilds in /var/cache/edb. Dependency info for all installed ebuilds is in a dep subdirectory which typically looks something like this:

.
├── usr
│   └── portage
│       ├── app-admin
│       │   ├── eselect-1.4.1
│       │   ├── eselect-lib-bin-symlink-0.1.1
│       │   ├── eselect-opengl-1.2.7
│       │   ├── gamin-0.1.10-r1
│       │   ├── logrotate-3.8.7
│       │   └── perl-cleaner-2.16
...

When portage needs to process dependency info, it reads those files. On a normal system, you will have a couple of hundred packages installed. This means that dependency processing does quite a bit of file processing.

Now if that dependency info was stored in some kind of database, wouldn’t that speed up dependency processing?

I stumbled over a wiki page describing how to switch portage’s metadata cache to sqlite. Even the portage man page talks about this - try running man portage and read the section about the modules file.

So I gave the sqlite metadata cache a try to measure if it really speeds up portage. After configuring the database and rebuilding the metadata cache, /var/cache/edb/dep looks a bit different now:

.
└── usr
    ├── portage
    └── portage.sqlite

Now let’s get to the interesting part: does the database really speed up portage? To measure, I ran a couple of emerge -vp commands using the normal setup and again using the database. The results are quite disappointing, though:

The best improvement was about 6% with the metadata database.

57% of the ebuilds did run slower with the metadata database, the worst increase was about 43%

So it looks like fiddling with portage’s metadata cache is not really worth the hassle.