To ease a future transition into joint quorums, this commit removes the
previous "ad-hoc" majority-based quorum and vote computations with that
introduced in the `raft/quorum` package.
More specifically, the progressTracker now uses a quorum.JointConfig for
which the "second" majority quorum is always empty; in this case the
quorum behaves like the one quorum.MajorityConfig that is actually
present. Or, more briefly, this change is a no-op, but it will take the
busywork out of actually starting to make use of joint quorums in the
future.
On a side node, I suspect that this might've fixed a bug regarding the
read index though I haven't been able to explicitly come up with a
counter-example. The problem was that the acks collected for the read
index weren't taking into account membership changes, so they'd run the
danger of using acks from nodes since removed to claim that a quorum of
acks had been received. There's a chance that there isn't a
counter-example (the only guarantee extracted from the "quorum" is that
there isn't another leader, but even if there's another leader all that
matters is that that leader doesn't have a divergent history from the
stale leader in the hypothetical counter-example), but either way there
is morally a bug here that is now fixed because VoteCommitted doesn't
care about votes from members that are not voters known to the currently
active configuration.
Instead of having disjoint mappings of ID to *Progress for voters and
learners, use a map[id]struct{} for each and share a map of *Progress
among them.
This is easier to handle when joint quorums are introduced, at which
point a node may be a voting member of two quorums.
The quorum package contains logic to reason about committed indexes as
well as vote outcomes for both majority and joint quorums. The package
is oblivious to the existence of learner replicas.
The plan is to hook this up to etcd/raft in subsequent commits.
We were already taking some precautions against learners campaigning,
but there was no safeguard against an explicit call to `Campaign()`.
The newly added test also verifies that leadership transfers to
learners are ignored.
This will keep them from diverging to much. In fact we should remove
some of the obvious differences that have crept in over time so that
what remains is structural. This isn't done in this commit since
it amounts to a change in the public API; we should lump this in
when we break the public API the next time.
Update to Go 1.12.5 testing. Remove deprecated unused and gosimple
pacakges, and mask staticcheck 1006. Also, fix unconvert errors related
to unnecessary type conversions and following staticcheck errors:
- remove redundant return statements
- use for range instead of for select
- use time.Since instead of time.Now().Sub
- omit comparison to bool constant
- replace T.Fatal and T.Fatalf in tests with T.Error and T.Fatalf respectively because the goroutine calls T.Fatal must be called in the same goroutine as the test
- fix error strings that should not be capitalized
- use sort.Strings(...) instead of sort.Sort(sort.StringSlice(...))
- use he status code of Canceled instead of grpc.ErrClientConnClosing which is deprecated
- use use status.Errorf instead of grpc.Errorf which is deprecated
Related #10528#10438
related: https://github.com/etcd-io/etcd/pull/10668
Provide a ref to the issue and PR management doc from the README,
similar to other references we have provided in the README.
