Bootstrap etcdserver from v3store (consistent_index)

[ahrtr]

What would you like to be added?

We have already deprecated v2store, and v3store is the solely source of truth for all data, including membership data in 3.6.0. But etcdserver still bootstrap from v2store, the latest v2 snapshot file. It will replay all WAL records starting from the latest snapshot index.

It doesn't make sense. We should bootstrap etcdserver from v3store, and replay WAL records start from the consistent_index.

It's the last blocker to completely get rid of the v2store.

Previous draft #17022

One problem is that etcdserver won't load any v2 snapshot on bootstrap anymore, accordingly it won't try to load any previous v3 snapshot which wasn't applied due to crash. two solutions:

• don't fix it, the leader will send a new snapshot. It means waste of bandwidth
• [preferred] still load valid snapshot entries from WAL, and if consistend-index < snapshot.index, try to load the v3 snapshot

The second one is still preferred, but depending on the complexity. If it greatly complicates the implementation, we might don't fix it. Will resolve this in the next step.

Why is this needed?

to completely get rid of v2store

[ahrtr]

Regarding the test, I think we can add a verification (see an example #19730) to ensure that etcdserver never applies entries <= consistent_index.

[hwdef]

/cc

[ahrtr]

/assign @fuweid

[github-actions]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed after 21 days if no further activity occurs. Thank you for your contributions.