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author Dirk Olmes <dirk@xanthippe.ping.de>
date Wed, 06 Dec 2017 17:05:27 +0100
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1 Title: speeding up portage's metadata cache
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2 Date: 2015-02-26
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3 Lang: en
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4 Tags: Gentoo
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6 [Gentoo's](http://www.gentoo.org) 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:
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8 .
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9 ├── usr
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10 │   └── portage
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11 │   ├── app-admin
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12 │   │   ├── eselect-1.4.1
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13 │   │   ├── eselect-lib-bin-symlink-0.1.1
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14 │   │   ├── eselect-opengl-1.2.7
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15 │   │   ├── gamin-0.1.10-r1
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16 │   │   ├── logrotate-3.8.7
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17 │   │   └── perl-cleaner-2.16
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18 ...
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20 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.
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22 Now if that dependency info was stored in some kind of database, wouldn't that speed up dependency processing?
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24 I stumbled over [a wiki page](http://gentoo-en.vfose.ru/wiki/Portage_SQLite_Cache) 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.
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26 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:
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28 .
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29 └── usr
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30    ├── portage
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31    └── portage.sqlite
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33 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:
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35 The best improvement was about 6% with the metadata database.
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37 57% of the ebuilds did run slower with the metadata database, the worst increase was about 43%
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39 So it looks like fiddling with portage's metadata cache is not really worth the hassle.