The intent is to make data returned by queries always conform to a
single schema version, which is requested by the client. For CQL
queries, for example, we want to use the same schema which was used to
compile the query. The other node expects to receive data conforming
to the requested schema.
Interface on shard level accepts schema_ptr, across nodes we use
table_schema_version UUID. To transfer schema_ptr across shards, we
use global_schema_ptr.
Because schema is identified with UUID across nodes, requestors must
be prepared for being queried for the definition of the schema. They
must hold a live schema_ptr around the request. This guarantees that
schema_registry will always know about the requested version. This is
not an issue because for queries the requestor needs to hold on to the
schema anyway to be able to interpret the results. But care must be
taken to always use the same schema version for making the request and
parsing the results.
Schema requesting across nodes is currently stubbed (throws runtime
exception).
Allows for having more than one clustering row range set, depending on
PK queried (although right now limited to one - which happens to be exactly
the number of mutiplexing paging needs... What a coincidence...)
Encapsulates the row_ranges member in a query function, and if needed holds
ranges outside the default one in an extra object.
Query result::builder::add_partition now fetches the correct row range for
the partition, and this is the range used in subsequent iteration.
In case of SELECT DISTINCT statments we are not intersted in clustering
keys at all. The only important information is whether partition key
exists and what's in static row (if it exists).
Signed-off-by: Paweł Dziepak <pdziepak@cloudius-systems.com>
Mutation query differs from data query in that returns information
needed to reconcile data slice with that retruned by other data
sources.
There is a generic mutation_query() algorithm introduced, which can
work with any mutation_source.
database::query_mutations() is a shard-local interface for mutation
queries.
The reconcilable_result is introduced as a medium for mutation query
results. It piggy backs on frozen_mutation as a medium for
reconcilable data.
