Static compact tables are tables with compact storage and no
clustering columns.
Before this patch, Scylla was writing rows of static compact tables as
clustered rows instead of static rows. That's because in our in-memory
model such tables have regular rows and no static row. In Cassandra's
schema (since 3.x), those tables have columns which are marked as
static and there are no regular columns.
This worked fine as long as Scylla was writing and reading those
sstables. But when importing sstables from Cassandra, our reader was
skipping the static row, since it's not present in the schema, and
returning no rows as a result. Also, Cassandra, and Scylla tools,
would have problems reading those sstables.
Fix this by writing rows for such tables the same way as Cassandra
does. In order to support rolling downgrade, we do that only when all
nodes are upgraded.
Fixes#4139.
47ca280e57