Digest only looks like live values, ignoring deletion
information. Equality should be consistent with that, so that schemas
considered equal do not trigger the alter path unnecessarily.
When migrating schema tables from v2 to v3, mutations underlying
table schema will change, and so will their digest. However, we want
the digest to be the same on new nodes as on the old nodes, because
schema exchange is not possible between the two nodes, so they
must to request schema definitions from each other.
The solution is to make the digest persistable, so that it sticks to
given table schema, surviving both migration and node restarts. On
migration from v2, the digest will be calculated from v2 mutations, so
it will be the same on new and old nodes.
It will be used to store Scylla spcific table metadata. We cannot
store it in the standard "tables" table for compatibility reasons -
Cassandra will fail to read schema if it encounteres columns it is not
expecting.
This patch allows a view schema to be frozen. To unfreeze such a
schema, we add an is_view attribute to the schema idl.
Signed-off-by: Duarte Nunes <duarte@scylladb.com>
We want the node's schema version to change whenever
table_schema_version of any table changes. The latter is calculated by
hashing mutations so we should also use mutation hash when calculating
schema digest.
We must use canonical_mutation form to allow for changes in the schema
of schema tables. The node which deserializes schema mutations may not
have the same version of the schema tables so we cannot use
frozen_mutation, which is a schema dependent form.
