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[mkgmap-dev] mkgmap doing excessive writing and converting to disk if used with --gmapi option

From Gerd Petermann gpetermann_muenchen at hotmail.com on Sun Sep 12 16:40:00 BST 2021

Hi Felix,

did not read all the posts in detail. I understand that mkgmap is neither burning SSDs nor doing any excessive writing unless you call it multiple times for the same input files. So the question is: Why do you do that?


Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag von Felix Hartmann <extremecarver at gmail.com>
Gesendet: Freitag, 10. September 2021 00:02
An: Development list for mkgmap
Betreff: Re: [mkgmap-dev] mkgmap doing excessive writing and converting to disk if used with --gmapi option

Well I think the .tmp files are just building up - and the renamed. So they are not causing any actual excessive write.
As for the gmap - it would be cool if there is a mode to not write them.

Actually it would be great if mkgmap could write all in one go. Because the thing that takes so much time - is the address search - and that is always the same. The differences are tiny (just because MapInstall is crashing when files are missing) you need to compile them separately.

but maybe there could be a mode where mkgamp writes all in one go.
So family-name / family-name1 / family-name2
description / description1 / description2
input input1 input2
(and maybe I missed some options are those that would need to be given for each set of input tiles. And then just an option where you tell mkgmap files starting with which first 4 numbers are relevant for address search. No need to analyze if those other supplied .img (e.g. buildings or contourlines) need to be added to address search.). I know coded around the problem of the gmap files causing excessive writes. But yeah that is actually really complicated be it on windows or linux...

On Wed, 8 Sept 2021 at 17:07, Felix Hartmann <extremecarver at gmail.com<mailto:extremecarver at gmail.com>> wrote:
Well I could give it 20 GB ram disk, maybe 32 but then I need to render on less than 12 processes 64GB ram available). But that is not enough for Asia continent map, and I guess super tight for Europe...

Mkgmap could definitely keep those .tmp files in memory. But the important bit is the gmap files not needeed to be written.... Also would save quite some CPU time.

On Wed, 8 Sep 2021, 14:31 ael <witwall3 at disroot.org<mailto:witwall3 at disroot.org>> wrote:
On Wed, Sep 08, 2021 at 02:10:52PM +0300, Felix Hartmann wrote:
> Yes on an nvme disk you barely notice the conversion - it's really quick.
> BUT it is not needed if you have the files and even more - it burns your
> NVME SSD disk.

+1. I always use an old spinning rust disk when using mkgmap to save ssd
write cycles, even without contours and such. It seems to be profligate
in its use of disk cycles. I did try using RAM disk, but even with 16GB
on a laptop, that was soon exhausted.


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Felix Hartman - Openmtbmap.org & VeloMap.org

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