we have a problem that could be very similar to the one mentioned in MDEV-17172.
When updating the charset of an empty backing table, we will no more get any results when calling the OQGRAPH table, i.e. every request returns an empty set.
It only happens in the following case:
The error does not seem to happen, if we remove the first `
SELECT * FROM graph;` query, so for us it seems like the state of the database is cached (or something alike) in the state before the ALTER TABLE call and when later adding data, it is not reflected in the graph table.
Recreating the graph table or restarting the database server helped in 95% of the time.