This patch adds a struct `per_request_options` used to communicate between CDC and upper abstraction layers. We need this for better compatibility with DynamoDB Streams in Alternator (https://github.com/scylladb/scylladb/issues/6918) to change operation types of log rows. This patch also adds a way to conditionally forward the item read by LWT to CDC and use it as a preimage. For now, only Alternator uses this feature.
The main changes are:
- add a struct `cdc::per_request_options` to pass information between CDC and upper abstraction layers,
- add the struct to `cas_request::apply`'s signature,
- add a possibility to provide a preimage fetched by an upper abstraction layer (to propagate a row read by Alternator to CDC's preimage). This reduces the number of reads-before-write by 1 for some **Alternator** requests and it is always safe. It's possible to use this feature also in CQL.
No backport, it's a feature.
Refs https://github.com/scylladb/scylladb/issues/6918
Refs https://github.com/scylladb/scylladb/pull/26121Closesscylladb/scylladb#26149
* github.com:scylladb/scylladb:
alternator, cdc: Re-use the row read by LWT as a CDC preimage
cdc: Support prefetched preimages
storage: Add cdc options to cas_request::apply
cdc, storage: Add a struct to pass per-mutation options to CDC
cdc: Move operations enum to the top of the namespace
61662bc562