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[mkgmap-dev] tile takes very long time to generate

From Mike Baggaley mike at tvage.co.uk on Mon Mar 8 08:59:25 GMT 2021

Hi Karl,

The first tile is likely to be generated with only a single thread running
whilst memory usage is checked, then the remainder may use both your
processors. If there is something about this tile that causes it to take a
long time, it may be worth moving it back in the list so that it doesn't
hold up starting of parallel processes, resulting in an overall reduction in
processing time.


-----Original Message-----
From: Gerd Petermann [mailto:gpetermann_muenchen at hotmail.com] 
Sent: 08 March 2021 06:32
To: Development list for mkgmap <mkgmap-dev at lists.mkgmap.org.uk>
Subject: Re: [mkgmap-dev] tile takes very long time to generate

Hi Karl,

I don't think that the order of the tiles should make a big difference. It
is quite normal that some tiles take longer than others, but 30 minutes is
far too long.
One well known reason for slow processing are very complex multipolygons
like Lake Huron. Another might be huge areas of sea. So, to find out if the
order or the content is causing the delay you can process the tiles in a
different order.
I often use VisualVM to monitor a running mkgmap, it helps to find out which
routines are called most often.
If you identify a single tile that takes very long (also with the default
style) you can upload that tile to http://files.mkgmap.org.uk/
Best is to add a small file with the options that were used, but you can
also post them here.
Hope that helps.


Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag von 7770
<7770 at foskan.eu>
Gesendet: Montag, 8. März 2021 06:53
An: mkgmap-dev at lists.mkgmap.org.uk
Betreff: [mkgmap-dev] tile takes very long time to generate


I observe a situation that one of the very first tiles (often the first or
third) that mkgmap generates takes 20 - 30 minutes to generate, wheres the
others take about 30 seconds each.

The map data produced by splitter is a total of around 700 files with
option --max-nodes=1275000.

sea and bouds are used for mkgmap.

At first i thought i am running low on memory but changing to max-jobs=1
(instead of the possible max of 2) did not make any change.

Is mkgmap doing something specific in the beginning that can explain this
time generating one of the very first tiles?

I can provide more details, let me know how i can best collect those details
in case i need to set some parameters to have mkgmap to say more about what
is doing.


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