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.

Introduce new parameters for alter system:
  - vdbe_max_steps
  - vtable_max_rows

Closes #1130

Add new files:
- storage/snapshot.rs: stuff related to raft snapshot
- storage/schema.rs: stuff related to DDL logic

Code is only moved, no changes to logic

It is now possible to write in migration `@_plugin_config.foo` where foo is
variable from plugin configuration. Note that configuration typically
belongs to individual services, in catalog this field is called entity. For
migration special values there is special entity called `migration_context`.
So corresponding alter looks this way:

ALTER PLUGIN p 0.1.0 SET migration_context.foo = '"nondefault"'

(extra quotes are temporary, and should be dealt with separately)

Closes https://git.picodata.io/picodata/picodata/picodata/-/issues/659

Add new config::AlterSystemParameters struct which is responsible
for definitions of system parameters, their default values and mapping
to sbroad type.

This is a big step towards moving all system parameters from
_pico_property into another system table.

Up to this patch `instance_uuid` and `replicaset_uuid` were generated
using name-based UUID v3. So all instances named `i1` in all clusters
had the same UUID.

With this patch UUIDs become random v4. Particular UUID values are
generated in two locations:

1. `start_boot` (src/lib.rs)
2. `handle_join_request_and_wait` -> `build_instance` (src/rpc/join.rs)

Function `Instance::new()` is removed in favor of explicit struct
construction.

godzie44 authored 7 months ago and Georgy Moshkin committed 6 months ago

Closes #664

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

feat: support ALTER SYSTEM. It allows to change whitelisted properties from _pico_property table. Currently, changes affect all tiers. Specifying tier will result in an error.

Co-Authored-by: Dmitry Rodionov <d.rodionov@picodata.io>

Co-Authored-by: Emir Vildanov <e.vildanov@picodata.io>

- Simplify code
- Check plugin exists on client side

- Move all preconditions checking to the client
- Return errors if preconditions fail instead of silently ignoring them

- Don't ignore operation if plugin is already enabled,
  the client must take care of this via the CaS ranges

- Don't propose mutliple Raft operations during one step as this may
  lead to inconsistencies in case of crashes