By "forever" in the summary I mean that I have never seen it finish, the longest I waited before interrupting was ~1 hour.

The test uses all default server startup options, loads original data set from MDEV-28073 (xpo_full_testcase.sql), runs ANALYZE PERSISTENT FOR ALL on all tables, and executes EXPLAIN for a query structured identically to MDEV-28073 (minus a couple of last JOINs), but the tables and fields in the query are mixed up - that is, different tables and fields from the dataset appear in different JOIN positions and conditions. The exact query will be provided.

A slight abnormality of this particular query is that one of ON conditions compares a datetime field to a string literal (not convertible into a proper date time), and thus produces Truncated incorrect datetime value warning (ER_TRUNCATED_WRONG_VALUE). I'm not sure whether it's a decisive factor for the problem, but it's possible. Except for this condition, the query is identical to MDEV-28928.

The query was executed with EXPLAIN FORMAT=JSON on several different versions/builds for comparison. All builds are non-debug.

|  4 | root | localhost:36260 | test | Query   |  590 | Statistics | EXPLAIN FORMAT=JSON SELECT * FROM ((((((((((((((((

...

It looks the same with optimizer_prune_level=2 (default) and 1.

MariaDB [test]> EXPLAIN FORMAT=JSON SELECT * FROM (((((((((((((((( 

...

1 row in set, 1 warning (36.832 sec)

MariaDB [test]> EXPLAIN FORMAT=JSON SELECT * FROM (((((((((((((((( 

...

1 row in set, 1 warning (9.314 sec)