raft: fix Ready.MustSync logic

[siddontang]

Refer etcd-io/etcd#10106

Seem that we have already used the Raft hard state, not the ready's, but we need to port the test.

Btw, seem that we don't consider Entries number for MustSync, see https://github.com/etcd-io/etcd/blob/b9b75f81e56241b0f573ba31b3c3a018290e9343/raft/node.go#L584

Do you know why? @BusyJay

[BusyJay]

I have no idea. 😿

[jayzhan211]

can someone specify which test cases need to be ported from etcd? or just modify the mustsync logic?

[BusyJay]

I think all the tests are ported. The issue is related to node, which is not available from raft-rs. We just implement raw_node.

@siddontang I believe it's because we don't sync all entries. We just sync those entries that are important like conf change or split. Although, it may not be good as a standalone library. Giving that we have been optimizing the performance of file syncing, I think it's OK to just sync all entries.

@accelsao I think you can modify mustsync logic and add a unit test.