I realized a test with osmconvert.
osmconvert file_original.pbf -o=file_o5m.o5m
osmconvert file_o5m.o5m -o=file_final.pbf
There is a difference of size between file_original.pbf and file_final.pbf
The file_final.pbf is smaller.
Can you explain the difference between the two files ?
Does it exist a difference of quality, precision for the map defined by the file_final.pbf ?
In final, the osmconvert will be use to append data in a database with the option –subtract.
Comment from Jochen Topf on 19 July 2018 at 13:46
You can use osmium fileinfo -e FILE to see a checksum of the contents of each of those files. If they are the same, the is no difference. If they are different you can use osmium diff to see what the differences are. Osmium is available from https://osmcode.org/osmium-tool.
osmium fileinfo -e FILE
There are different ways of encoding OSM data in a PBF file. You can use different block sizes or order the internal string table in different ways. This will result in slightly different file sizes. See https://wiki.osm.org/wiki/PBF_Format for details of the format.
Oh, and I suggest using help.osm.org for questions. Just so this here by chance, on help.osm.org probably more people will see it.