Why ways importing speed depends on imported nodes? Is it memory allocation bug?

[likemusic]

I'v tested import on Chicago extract (51MB) from bbbike in pbf format.

The result is above: 652 - 26 (k/s for nodes and ways).

Then I extract only ways from file ( osmconvert --drop-nodes --drop-relations --out-pbf -o=$RESULT_NAME-nodes.osm.pbf $OSM_SOURCE) and run import again and I have the results: 0 - 9 .

Why for file with nodes ways imported almost x3 faster then for file without nodes?

To exclude the possibility of influence of the pbf-file format I extracted nodes from source file (osmconvert --drop-ways --drop-relations --out-pbf -o=$RESULT_NAME-nodes.osm.pbf $OSM_SOURCE) and then merge nodes with ways (osmium cat -o $RESULT_FILE -f osm.pbf,add_metadata=false $NODES_FILE $WAYS_FILE ) and have the same results like for source file (652 - 26).

Also I've tested import source file without cache (--cache=0) and I've got ways import speed 9k/s, like for only ways files.

Its seems like ways buffer depends on nodes buffer and it not used when imported pbf-file without nodes.

At the same time, when I import full planet file, I've got ways import speed just 0.89k/s. But when I extract only ways from planet file I'v got speed 9-12 k/s for ways.

Any ideas why is this happens?

Any suggestion how to debug where is the bottleneck and how to avoid it?

My environment:

# osm2pgsql --version
2021-03-19 20:11:36  osm2pgsql version 1.4.1 (1.4.1-16-gf7993c95)
Compiled using the following library versions:
Libosmium 2.16.0
Proj [API 4] Rel. 6.3.1, February 10th, 2020
Lua 5.2.4

# sudo --user=postgres osm2pgsql --create --slim --database=gis --merc --hstore-all --style=hstore-only.style --tag-transform-script=openstreetmap-carto.lua --prefix=planet_osm_hstore --number-processes=$NumberProcesses --cache=$CacheSizeMb $OSM_EXTRACT

CacheSizeMb=16000

[joto]

OSM files without nodes don't make much sense. Without nodes, there is no geometry for the ways so there is nothing to import into the database. And then it is much faster, because there is no work to do.