Importing large dataset with osm2psql?

I imported a Planet File on a 24Gb Machine (Ubuntu Trusty) with the following ..

bzcat planet-latest.osm.bz2 | 
osm2pgsql --verbose -U YourUser --flat-nodes flat-nodes --keep-coastlines --cache 24000 --hstore --hstore-add-index --tablespace-index pg_default --exclude-invalid-polygon --number-processes 6 --unlogged --cache-strategy dense --extra-attributes --slim -H localhost -d planetosm --style ../my.style planet-latest.osm.bz2

It took approx 5 days, the last half on the database side .. rather than actual import

I tuned Postgres with the following for the import

autovacuum = off (default #autovacuum = on)
checkpoint_segments = 60 (default #checkpoint_segments = 3 # in logfile      
segments, min 1, 16MB each)
maintenance_work_mem = 256MB ( default #maintenance_work_mem = 16MB # min 1MB)
work_mem = 256MB (default #work_mem = 1MB  # min 64kB)

Your computer should be fine for importing Europe.

Given your dataset size and computer, I'd recommend something like this

I'm assuming that you have an 8 thread CPU, if not, adjust --number-processes.

You don't need 25GB of ram for cache with just Europe.

For Europe, flat nodes should be smaller and faster than in-DB storage of node positions.

If there are still problems, check that you have a version of osm2pgsql using the 64-bit ID space and if so, check your PostgreSQL settings. You could be filling up your disk. Try tuning your settings in postgresql.conf.