Commit a6ad70d3da changed the format of
stream IDs: the lower 8 bytes were previously generated randomly, now
some of them have semantics. In particular, the least significant byte
contains a version (stream IDs might evolve with further releases).
This is a backward-incompatible change: the code won't properly handle
stream IDs with all lower 8 bytes generated randomly. To protect us from
subtle bugs, the code has an assertion that checks the stream ID's
version.
This means that if an experimental user used CDC before the change and
then upgraded, they might hit the assertion when a node attempts to
retrieve a CDC generation with old stream IDs from the CDC description
tables and then decode it.
In effect, the user won't even be able to start a node.
Similarly as with the case described in
d89b7a0548, the simplest fix is to rename
the tables. This fix must get merged in before CDC goes out of
experimental.
Now, if the user upgrades their cluster from a pre-rename version, the
node will simply complain that it can't obtain the CDC generation
instead of preventing the cluster from working. The user will be able to
use CDC after running checkAndRepairCDCStreams.
Since a new table is added to the system_distributed keyspace, the
cluster's schema has changed, so sstables and digests need to be
regenerated for schema_digest_test.
Commit 968177da04 has changed the schema
of cdc_topology_description and cdc_description tables in the
system_distributed keyspace.
Unfortunately this was a backwards-incompatible change: these tables
would always be created, irrespective of whether or not "experimental"
was enabled. They just wouldn't be populated with experimental=off.
If the user now tries to upgrade Scylla from a version before this change
to a version after this change, it will work as long as CDC is protected
b the experimental flag and the flag is off.
However, if we drop the flag, or if the user turns experimental on,
weird things will happen, such as nodes refusing to start because they
try to populate cdc_topology_description while assuming a different schema
for this table.
The simplest fix for this problem is to rename the tables. This fix must
get merged in before CDC goes out of experimental.
If the user upgrades his cluster from a pre-rename version, he will simply
have two garbage tables that he is free to delete after upgrading.
sstables and digests need to be regenerated for schema_digest_test since
this commit effectively adds new tables to the system_distributed keyspace.
This doesn't result in schema disagreement because the table is
announced to all nodes through the migration manager.
