Review Request 113485: Speed up natural sorting by first sorting the items according to KFileItem::text() with QString::operator<()

[Mark Gaiser]

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Hi Frank,

That's one hell of a lot faster! It still doesn't beat..... <ok, i just skip it> ;)

I do have one suggestion for you that might make it even faster.
What you don't see doesn't have to be sorted, right? And to get that done, you might be able to use std::partial_sort [1]

Lets say this is your entire folder (in ascii)

54
2
564
32
1
678
234
23
21
866
12
8
45

Lets say that this is your view:
54
2
564
------- top part of view
32
1
678
234
23
21
------- bottom part of view
866
12
8
45

Now partial_sort is able(?) to do this (not tested so i could be wrong). Same view partial sorted.
...
54
2
564
------- top part of view
...
8
12
21
23
...
------- bottom part of view
866
45
...

I know the above does work if you start from the top. I'm not 100% if it also works from the middle of a view. If it works then sorting can be reduced to the items you see. This would make the sorting insanely faster since all you have to sort would be about 100 entries at most, more aren't on the screen at any given time. Doing that would probably mean that you have to maintain which parts are sorted just to prevent needless resorting when the user scrolls up/down.

[1] http://en.cppreference.com/w/cpp/algorithm/partial_sort

- Mark Gaiser


On Oct. 28, 2013, 6:46 p.m., Frank Reininghaus wrote:
> 
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> http://git.reviewboard.kde.org/r/113485/
> -----------------------------------------------------------
> 
> (Updated Oct. 28, 2013, 6:46 p.m.)
> 
> 
> Review request for Dolphin.
> 
> 
> Repository: kde-baseapps
> 
> 
> Description
> -------
> 
> We all know now that natural sorting can be very slow. There are two ways to improve this:
> 
> 1. Make the "natural comparison" of two items faster. We might be able to do this when we can use QCollator from Qt5.
> 
> 2. Reduce the number of (expensive) comparisons.
> 
> This patch implements option 2 by first doing a very fast non-natural sorting of the items according to their name. The resulting sequence of items is partially sorted even according to the "natural" comparison, and this makes it possible to do the final sorting with a far lower number of comparisons.
> 
> 
> Diffs
> -----
> 
>   dolphin/src/kitemviews/kfileitemmodel.h d005705 
>   dolphin/src/kitemviews/kfileitemmodel.cpp f21edbf 
> 
> Diff: http://git.reviewboard.kde.org/r/113485/diff/
> 
> 
> Testing
> -------
> 
> Loaded a folder with 100,000 items with the names "a1.txt", ..., "a100000.txt". I guess that this is also one of the worst cases with respect to "difference between natural and non-natural sort order".
> 
> This patch reduces the time needed to sort in a release build (commented out the profiling output in insertItems()) from 1940 ms to 714 ms, which is a saving of about 63%.
> 
> 
> Thanks,
> 
> Frank Reininghaus
> 
>

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