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

Tasks/PRs in v3.7

• Do not load v2 snapshot on bootstrap #21107
  • After this PR, etcd 3.7 won't load v2 snapshot at all on bootstrap.
  • But etcd 3.7 still needs to generate v2 snapshot so as to be compatible with 3.6. We are going to remove it in 3.8.
• Initialize confState from v3 store on bootstrap #21138
  • build confState from v3store; and don't apply confChange to raft if it's already applied, so that we can avoid the issue mentioned in Remove v2 store #20139 (comment).
  • This PR depends on raft side change: Allow users to pass in a snapshot with only the ConfState initialized during bootstrap raft#370
• Remove flag --max-snapshots in 3.8 rather than 3.7 #21160
  • Also backported to 3.6: [release-3.6] Remove flag --max-snapshots in 3.8 rather than 3.7 #21161
• Keep the --snapshot-count flag #21162
  • Also backported to 3.6: [release-3.6] Keep the --snapshot-count flag #21163
• Update 3.6 changelog to cover the two flags deprecation changes #21164
• Document work
  • We just need to call this out in 3.7 release doc. No separate doc needed.

Tasks planned in v3.8

• Do not generate v2 snapshot files anymore
• Remove flag --max-snapshots
• Remove flag --v2-deprecation