This makes (bbolt) backend a full feature snapshot in term of WAL/raft,
i.e. carries:
- commit : (applied_index)
- confState
Benefits:
- Backend will be a sufficient point in time definition sufficient to
start replaying WAL. We have applied_index & confState in consistent
state.
- In case of emergency a backend state can be used for recovery
Flags `--experimental-enable-v2v3` and '-enable-v2' will raise a warning in 3.5,
in 3.6 they are schedule for decomissioning, such that v2store can stop be written in 3.7.
Deprecation plan in: https://github.com/etcd-io/etcd/issues/12913
Every transaction committed to backend is writing most recent consistent_index.
Makes sure that even automatically trigger commits of batch-transactions
stays "really" consistent a.d. the most recent WAL log index applied.
clientv3 logs (especially tests) were poluted with unattributed to testing.T log lines:
```
{"level":"warn","ts":"2021-04-29T12:42:11.055+0200","logger":"etcd-client","caller":"v3/retry_interceptor.go:64","msg":"retrying of unary invoker failed","target":"etcd-endpoints://0xc0000fafc0/#initially=[unix://localhost:m10]","attempt":0,"error":"rpc error: code = ResourceExhausted desc = etcdserver: mvcc: database space exceeded"}
```
The reasons were 2 fold:
- Interceptors were copying logger before "WithLogger" could modify it.
- We were not propagating the loggers in a few testing contexts.
Prior to this CL, `ETCDCTL_API=2 etcdctl backup --with-v3` was readacting WAL log
(by removal of some entries), but was NOT updating consistent_index in the backend.
Also the WAL editing logic was buggy, as it didn't took in consideration the fact
that when TERM changes, there can be entries with duplicated indexes in
the log. So its NOT sufficient to subtract number of removed entries to
get accurate log indexes.
The PR replaces removing and shifting of WAL entries with replacing them with an no-op entries.
Thanks to this consistent-index references are staying up to date.
The PR also:
- updates 'verification' logic to check whether consistent_index does not lag befor last snapshot
- env-gated execution of verification framework in `etcdctl backup`.
Tested with:
```
(./build.sh && cd tests && EXPECT_DEBUG=TRUE 'env' 'go' 'test' '-timeout=300m' 'go.etcd.io/etcd/tests/v3/e2e' -run=TestCtlV2Backup --count=1000 2>&1 | tee TestCtlV2BackupV3.log)
```
