Georgy Moshkin authored 2 years ago and Yaroslav Dynnikov committed 2 years ago

Tarantool synchronous replication is broken in such a way, that local
& asynchronous transactions get rolled back upon synchronous
transaction rollback. This is critical for us, because we use local
spaces for the raft log, which should be orthogonal to synchronous
business spaces, but is not due to this behavior. Until it is fixed, we
will not use synchronous replication.

See https://github.com/tarantool/tarantool/issues/7903

Rewrite it from scratch to satisfy tests and to represent governor
logics in general.

No assumptions should be made on `traft::node::Status.leader_id`. It can
be set to `None` at any time due to a re-election.

Lots of tests are marked "fixme" with the desired value commented.
They'll be fixed in the next commit.

Cases covered:
- when someone goes offline
- whenever vshard gets reconfigured

Georgy Moshkin authored 2 years ago and Georgy Moshkin committed 2 years ago

Currently stores:
- replicset_id
- replicaset_uuid
- sharding weight
- replication master id

Yaroslav Dynnikov authored 2 years ago and Yaroslav Dynnikov committed 2 years ago

Only a few functions are allowed in signal handlers (see `man 7
signal-safety`). Both `println!()` and `std::process::exit()` are not
acceptable. In our case `std::process::exit()` resulted in a dead lock
when called concurrently.

This patch fixes it, and also enhances some other aspects of the supervisor.

See also: https://stackoverflow.com/questions/44865737/println-panics-when-called-concurrently

Yaroslav Dynnikov authored 2 years ago and Yaroslav Dynnikov committed 2 years ago

This commit slignly changes the order of entries in the raft log:
ConfChange now comes at the first place before other Ops, but that's ok.

Yaroslav Dynnikov authored 2 years ago and Yaroslav Dynnikov committed 2 years ago

Do it only when the governor tells to. When `_G.vshard == nil`, it's
more alike `traft::node::global()` which reurns either `Ok` or
`Err(Uninitialized)`.

Yaroslav Dynnikov authored 2 years ago and Yaroslav Dynnikov committed 2 years ago

It produces better error messages.

Before this commit:

```
tarantool> vshard.router.call()
---
- error: '[string "local log = require(''log'')..."]:575: attempt to
    compare number with nil'
...
```

With this commit:

```
- error: 'vshard/router/init.lua:575: attempt to compare number with
    nil'
```