Review Request 111050: Fast mime detection speedup.

Mark Gaiser markg85 at
Sun Oct 27 18:55:57 GMT 2013

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(Updated Oct. 27, 2013, 6:55 p.m.)


This change has been discarded.

Review request for kdelibs, David Faure and Frank Reininghaus.

Repository: kdelibs



I've recently seen Frank Reininghaus do his best in speeding up the rendering in dolphin with regards to the app icons. And trying to prevent icon flickering between "unknown" and the actual icon.

While reading his posts on the mailing list i was beginning to wonder: "is fast mime detection actually fast"? While it was certainly faster then "slow" mime detection, it still didn't really seem fast to me. A small benchmark app hat ran fast mime detection in /usr/bin took ~40ms to complete. That's for just 2656 items.

After quite a bit of profiling i managed to to bring the duration down from ~40ms to ~3ms sometimes ~4ms. That's well over 10x faster.
Mime detection by extension (like "") is done as follows:
Loop - find first dot
- "tar.gz"
if that matches a mime type then it's returned if it doesn't then it proceeds on to the next dot:
- next dot: "gz"
if that matches.. return.
Otherwise it will return the default mime type.

I am getting an inconsistency. Using the unpatched fast mime detection on a file like: "test.tar.gz" gets detected as "application-x-compressed-tar" where the patched version detects it as "application-gzip". The slow and detailed mime detection detects the same file as "application-x-compressed-tar". What should it be? application-gzip or application-x-compressed-tar?

Note: This improved detection does expect folders to end with a "/". Otherwise they will be detected as application-octet-stream (the default). But i think this is common sense to let folders end with a "/". If any apps that don't do that, they should fix it i suppose.

Best thing, it's all internal and private api change. No public function is changed.

All feedback is welcome! If possible, i would like to put this in KDE 4.11.


  kdecore/services/kmimetype.h bc35bcf 
  kdecore/services/kmimetype.cpp d748523 
  kdecore/services/kmimetyperepository.cpp f56f48e 



Tested this using just output comparison between the old version and the new implementation. It works just fine.
kurlmimetest output:
********* Start testing of KUrlMimeTest *********
Config: Using QTest library 4.8.4, Qt 4.8.4
PASS   : KUrlMimeTest::initTestCase()
PASS   : KUrlMimeTest::testURLList()
PASS   : KUrlMimeTest::testOneURL()
PASS   : KUrlMimeTest::testFromQUrl()
PASS   : KUrlMimeTest::testMostLocalUrlList()
PASS   : KUrlMimeTest::cleanupTestCase()
Totals: 6 passed, 0 failed, 0 skipped
********* Finished testing of KUrlMimeTest *********


Mark Gaiser

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