We have one replication of reference table for each node. Therefore all problems with
replication factor > 1 also applies to reference table. As a solution we will not allow
foreign keys on reference tables. It is not possible to define foreign key from, to or
between reference tables.
With this PR, we add foreign key support to ALTER TABLE commands. For now,
we only support foreign constraint creation via ALTER TABLE query, if it
is only subcommand in ALTER TABLE subcommand list.
We also only allow foreign key creation if replication factor is 1.
With this change, we now push down foreign key constraints created during CREATE TABLE
statements. We also start to send foreign constraints during shard move along with
other DDL statements
Onder Kalaci
Marco Slot
Burak Yucesoy