GNU bug report logs - #44053
Poor profile generation performance on spinning disks

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From: Ludovic Courtès <ludo <at> gnu.org>
To: zimoun <zimon.toutoune <at> gmail.com>
Cc: guix-devel <guix-devel <at> gnu.org>, Luis Felipe <luis.felipe.la <at> protonmail.com>, 44053 <at> debbugs.gnu.org, Maxim Cournoyer <maxim.cournoyer <at> gmail.com>
Subject: bug#44053: ‘xdg-mime-database’ profile hook is slow
Date: Mon, 02 Nov 2020 13:53:18 +0100

Ludovic Courtès <ludo <at> gnu.org> skribis:

> Apart from LibreOffice, I found that ‘share/mime/packages’ is provided
> by at least: hugin, gcr, fontforge.  Most GUI packages don’t have it.
> So in practice, we’re often rebuilding the exact same database.

On closer inspection, the time-consuming bit is processing
‘share/mime/packages/freedesktop.org.xml’ (from ‘shared-mime-info’),
which is quite large and leads to the creation of hundreds of file.  We
end up re-processing it every time.  This is particularly wasteful
because the ‘shared-mime-info’ package already contains the result of
applying ‘update-mime-database’ to itself.

Unfortunately, AIUI,

  update-mime-database(X ∪ Y) ≠ update-mime-database(X) ∪ update-mime-database(Y)

(For example, the files
‘share/mime/{globs,magic,XMLnamespaces,subclasses,aliases,types,generic-icons,icons,treemagic,mime.cache}’
concatenate info from X and Y.)

So it would seem we cannot simply used the pre-built database from
‘shared-mime-info’ and merge it with that of the other packages, at
least not without changing ‘update-mime-database’ or re-implementing
parts of it on our side.

Ludo’.

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