TopologyCache is a collection of deserialized structures with
information about cluster topology. This currently includes data from
_pico_instance, _pico_replicaset, _pico_tier & _pico_service_route_table.
The info is automatically kept up to date with the corresponding system
tables. The TopologyCache also caches the immutable info related to the
current instance, like instance name, replicaset uuid, etc.

From now on we should be reading this data from TopologyCache whenever
possible instead of going directly to system tables as we were doing
previosly.

At the moment only the plugin RPC module has transitioned to using
TopologyCache but other modules should be refactored as well.
Especially governor.

Before this fix if requesting RPC by an invalid bucket_id we would send
an RPC to every replicaset to check if they have such a bucket_id.
This is not needed because we know the allowed range.

Closes #1130

Added tier parameter to plugin RPC target BucketId

Move vshard related fields from _pico_property to _pico_tier
and adapt it in governor algorithm

Georgy Moshkin authored 8 months ago and Yaroslav Dynnikov committed 8 months ago

This fixes the A-B-A problem which was observed in the issue
https://git.picodata.io/picodata/picodata/picodata/-/issues/763.

Closes #763

- use RouteBuilder to register rpc endpoints (input and ouptut is raw
  bytes for now)
- use RequestBuilder to send RPC requests to other instances which are
  running a specified plugin.service (guarded by version)
    - supported routing by
        - explicit instance_id
        - replicaset_id
        - bucket_id
        - any available instance with given service
- use context::Context to extract information about request or add
  custom fields at runtime (middleware not yet implemented)

- Now we explicitly store the current & target vshard configuration in
  global storage