We have seen users unintentionally use RF=1 or RF=2 for a keyspace.
We would like to have an option for a minimal RF that is allowed.
Cassandra recently added, in Cassandra 4.1 (see apache/cassandra@5fdadb2
and https://issues.apache.org/jira/browse/CASSANDRA-14557), exactly such
a option, called "minimum_keyspace_rf" - so we chose to use the same option
name in Scylla too. This means that unlike the previous "safe mode"
options, the name of this option doesn't start with "restrict_".
The value of the minimum_keyspace_rf option is a number, and lower
replication factors are rejected with an error like:
cqlsh> CREATE KEYSPACE x WITH REPLICATION = { 'class' : 'SimpleStrategy',
'replication_factor': 2 };
ConfigurationException: Replication factor replication_factor=2 is
forbidden by the current configuration setting of minimum_keyspace_rf=3.
Please increase replication factor, or lower minimum_keyspace_rf set in
the configuration.
This restriction applies to both CREATE KEYSPACE and ALTER KEYSPACE
operations. It applies to both SimpleStrategy and NetworkTopologyStrategy,
for all DCs or a specific DC. However, a replication factor of zero (0)
is *not* forbidden - this is the way to explicitly request not to
replicate (at all, or in a specific DC).
For the time being, minimum_keyspace_rf=0 is still the default, which
means that any replication factor is allowed, as before. We can easily
change this default in a followup patch.
Note that in the current implementation, trying to use RF below
minimum_keyspace_rf is always an error - we don't have a syntax
to make into just a warning. In any case the error message explains
exactly which configuration option is responsible for this restriction.
Fixes#8891.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Closes#9830
cdedc79050