We want to disable `migration_manager` schema pulls and make schema
managed only by Raft group 0 if Raft is enabled. This will be important
with Raft-based topology, when schema will depend on topology (e.g. for
tablets).
We solved the problem partially in PR #13695. However, it's still
possible for a bootstrapping node to pull schema in the early part of
bootstrap procedure, before it setups group 0, because of how the
currently used `_raft_gr.using_raft()` check is implemented.
Here's the list of cases:
- If a node is bootstrapping in non-Raft mode, schema pulls must remain
enabled.
- If a node is bootstrapping in Raft mode, it should never perform a
schema pull.
- If a bootstrapped node is restarting in non-Raft mode but with Raft
feature enabled (which means we should start upgrading to use Raft),
or restarting in the middle of Raft upgrade procedure, schema pulls must
remain enabled until the Raft upgrade procedure finishes.
This is also the case of restarting after RECOVERY.
- If a bootstrapped node is restarting in Raft mode, it should never
perform a schema pull.
The `raft_group0` service is responsible for setting up Raft during boot
and for the Raft upgrade procedure. So this is the most natural place to
make the decision that schema pulls should be disabled. Instead of
trying to come up with a correct condition that fully covers the above
list of cases, store a `bool` inside `migration_manager` and set it from
`raft_group0` function at the right moment - when we decide that we
should boot in Raft mode, or restart with Raft, or upgrade. Most of the
conditions are already checked in `setup_group0_if_exist`, we just need
to set the bool. Also print a log message when schema pulls are
disabled.
Fix a small bug in `migration_manager::get_schema_for_write` - it was
possible for the function to mark schema as synced without actually
syncing it if it was running concurrently to the Raft upgrade procedure.
Correct some typos in comments and update the comments.
Fixes#12870Closes#14428
* github.com:scylladb/scylladb:
raft_group_registry: remove `has_group0()`
raft_group0_client: remove `using_raft()`
migration_manager: disable schema pulls when schema is Raft-managed
7d35cf8657