[OSM-dev] osm2pgsql patch for nested relations

["Petr Morávek [Xificurk]"]

Darafei Praliaskouski wrote:
> I am not using route= relations in osm2pgsql. Is there a way to skip their 
> processing, to get more speed than 4 relations/sec?

This is bothering me for some time now... I don't know the code of
osm2pgsql, but what's striking me is the influence of fsync=on/off on
the speed of processing relations.

I'm importing only a small extract of OSM data, postgres has pretty
generous memory settings. Funny thing happens when I turn off fsync -
the only significant speed up is in the stage "processing relations",
all other stages complete in roughly same times.

fsync=on
Relation stats: total(70149), max(2061958) in 1524s
Osm2pgsql took 3194s overall

fsync=off
Relation stats: total(70149), max(2061958) in 248s
Osm2pgsql took 1864s overall

So overall fsync=off is over 40% faster than fsync=on, and almost all is
due to the speed up in "processing relations" stage.

Best regards,
Petr Morávek aka Xificurk
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