Example "public-transport.lua" fails with error: ERROR: Database format for tags invalid.

[Xyaren]

What version of osm2pgsql are you using?

osm2pgsql version 2.0.1
Build: None
Compiled using the following library versions:
Libosmium 2.20.0
Proj 9.5.1
Lua 5.3.6

What operating system and PostgreSQL/PostGIS version are you using?

ubuntu:25.04 on Docker

Tell us something about your system

Irrelevant

What did you do exactly?

Using PBF https://download.geofabrik.de/europe/cyprus-latest.osm.pbf to test around with a small dataset
Imported using flex style from examples: flex-config/public-transport.lua

Command osm2pgsql --create --slim --database postgresql://osmuser@db/osm --schema public --middle-schema public --output=flex --style=./public-transport.lua --log-progress=true ./data/cyprus-latest.osm.pbf

The database is running on docker using the postgis/postgis image.

What did you expect to happen?

Data to be imported without issues.

What did happen instead?

Encountered an error:

2025-01-16 16:08:21  osm2pgsql version 2.0.1
2025-01-16 16:08:22  Database version: 17.2 (Debian 17.2-1.pgdg110+1)
2025-01-16 16:08:22  PostGIS version: 3.5
2025-01-16 16:08:22  Initializing properties table '"public"."osm2pgsql_properties"'.
2025-01-16 16:08:22  Storing properties to table '"public"."osm2pgsql_properties"'.
2025-01-16 16:08:55  Reading input files done in 33s.
2025-01-16 16:08:55    Processed 4167670 nodes in 24s - 174k/s
2025-01-16 16:08:55    Processed 472207 ways in 6s - 79k/s
2025-01-16 16:08:55    Processed 8641 relations in 3s - 3k/s
2025-01-16 16:08:55  Reprocess marked nodes/ways (stage 2)...
2025-01-16 16:08:55  Creating id index on table 'lines'...
2025-01-16 16:08:55  Creating id indexes took 0s
2025-01-16 16:08:55  There are 676 nodes to reprocess...
2025-01-16 16:08:55  ERROR: Database format for tags invalid.

What did you do to try analyzing the problem?

Looked into the database.
All tags columns are of type jsonb

I was actually working on a different example that failed in the same way. Then I used the example and encountered the same issue.
I tried some other flex styles and they work as long as no 2nd stage is involved.

[joto]

I checked this and you are right, this is a bug. Thanks for reporting this. Osm2pgsql sends the wrong database query and then doesn't understand the answer. This happens only in slim mode, when two-stage processing is used with node members of a relation. So the workaround for the moment is to use non-slim mode.