The function `check_exists` checks whether a given table exists, giving
an error otherwise. It previously used `on_internal_error`.
`check_exists` is used in some old functions that insert CDC metadata to
CDC tables. These tables are no longer used in newer Scylla versions
(they were replaced with other tables with different schema), and this
function is no longer called. The table definitions were removed and
these tables are no longer created. They will only exists in clusters
that were upgraded from old versions of Scylla (4.3) through a sequence
of upgrades.
If you tried to upgrade from a very old version of Scylla which had
neither the old or the new tables to a modern version, say from 4.2 to
5.0, you would get `on_internal_error` from this `check_exists`
function. Fortunately:
1. we don't support such upgrade paths
2. `on_internal_error` in production clusters does not crash the system,
only throws. The exception would be catched, printed, and the system
would run (just without CDC - until you finished upgrade and called
the propoer nodetool command to fix the CDC module).
Unfortunately, there is a dtest (`partitioner_tests.py`) which performs
an unsupported upgrade scenario - it starts Scylla from Cassandra (!)
work directories, which is like upgrading from a very old version of
Scylla.
This dtest was not failing due to another bug which masked the problem.
When we try to fix the bug - see #11225 - the dtest starts hitting the
assertion in `check_exists`. Because it's a test, we configure
`on_internal_error` to crash the system.
The point of this commit is to not crash the system in this rare
scenario which happens only in some weird tests. We now throw
`std::runtime_error` instead of calling `on_internal_error`. In the
dtest, we already ignore the resulting CDC error appearing in the logs
(see scylladb/scylla-dtest#2804). Together with this change, we'll be
able to fix the #11225 bug and pass this test.
Closes#11287
b4c5b79f5e