pg_upgrade from PostgreSQL 17 → 18 fails

[said-karimov-aiven]

Now that PostgreSQL 18 preserves the optimizer statistics during an upgrade with dump/restore or pg_upgrade, the upgrade fails if postgresql-unit extension installed. When upgrading a cluster from PostgreSQL 17 to 18, the process fails during the statistics–restore phase with:

pg_restore: while PROCESSING TOC:
pg_restore: from TOC entry 4602; 0 0 STATISTICS DATA foo (no owner)
pg_restore: error: could not execute query: ERROR: unit "km" is not known
Command was: SELECT * FROM pg_catalog.pg_restore_relation_stats(
'version', '170007'::integer,
'schemaname', 'public',
'relname', 'foo',
'relpages', '1'::integer,
'reltuples', '10'::real,
'relallvisible', '1'::integer
);

SELECT * FROM pg_catalog.pg_restore_attribute_stats(
'version', '170007'::integer,
'schemaname', 'public',
'relname', 'foo',
'attname', 'munit',
'inherited', 'f'::boolean,
'null_frac', '0'::real,
'avg_width', '16'::integer,
'n_distinct', '-1'::real,
'histogram_bounds', '{"3.20040000000000013 m","10 m","15 m","20 m","25.4000000000000021 m","30.4800000000000004 m","1.5 km","8.04672000000000054 km","19.3121279999999977 Mm","9.46073047258080102 Pm"}'::text,
'correlation', '0.15151516'::real
);

The failure occurs when pg_restore attempts to restore STATISTICS DATA for a table (foo in this case) containing a column of type unit. This happens despite unit_prefixes and unit_units already being "populated" in unit*.sql.in files.