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release-22.2: kvserver: don't quiesce with follower in StateProbe #103877

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merged 1 commit into from
May 25, 2023

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@tbg tbg commented May 25, 2023

Backport 1/1 commits from #103827.

/cc @cockroachdb/release

Release justification: partially avoids a bug that could lead to lease transfers being rejected.


shouldReplicaQuiesce checks that all followers are fully caught up, but it's
still possible to have a follower in StateProbe (because we call
rawNode.ReportUnreachable when an outgoing message gets dropped).

Persistent StateProbe is problematic: we check for it before lease transfers, so
despite the follower being fully caught up, we'd refuse the transfer.

Unfortunately, this commit itself is not enough: even if the range is not
quiesced, it needs to replicate a new entry to rectify the situation (i.e.
switch follower back to StateReplicate). This is because at the time of writing,
receipt of a heartbeat response from the follower is not enough to move it back
to StateReplicate.
This was fixed upstream, in #103826.

However, this is still not enough! If the range quiesces successfully, and
then ReportUnreachable is called, we still end up in the same state; this is now tracked in #103828.

I ran into the above issue on
#99191, which adds persistent
circuit breakers, when stressing TestStoreMetrics. That test happens to
restart n2 when it's fully caught up and due to the persistence of the circuit
breakers when it comes up the leader will move it into StateProbe (since we can
end up dropping the first heartbeat sent to it as it comes up, since the breaker
hasn't untripped yet).

But, I believe that this bug is real even without this breaker re-work, just
harder to trigger.

Epic: none
Release note (bug fix): fixed a problem that could lead to erroneously refused
lease transfers (error message: "refusing to transfer lease to [...] because
target may need a Raft snapshot: replica in StateProbe"

shouldReplicaQuiesce checks that all followers are fully caught up, but it's
still possible to have a follower in StateProbe (because we call
`rawNode.ReportUnreachable` when an outgoing message gets dropped).

Persistent StateProbe is problematic: we check for it before lease transfers, so
despite the follower being fully caught up, we'd refuse the transfer.

Unfortunately, this commit itself is not enough: even if the range is not
quiesced, it needs to replicate a new entry to rectify the situation (i.e.
switch follower back to StateReplicate). This is because at the time of writing,
receipt of a heartbeat response from the follower is not enough to move it back
to StateReplicate.
This was fixed upstream, in cockroachdb#103826.

However, this is still not enough! If the range quiesces successfully, and
*then* `ReportUnreachable` is called, we still end up in the same state.

TODO file issue about this.

I ran into the above issue on
cockroachdb#99191, which adds persistent
circuit breakers, when stressing `TestStoreMetrics`. That test happens to
restart n2 when it's fully caught up and due to the persistence of the circuit
breakers when it comes up the leader will move it into StateProbe (since we can
end up dropping the first heartbeat sent to it as it comes up, since the breaker
hasn't untripped yet).

But, I believe that this bug is real even without this breaker re-work, just
harder to trigger.

Epic: none
Release note (bug fix): fixed a problem that could lead to erroneously refused
lease transfers (error message: "refusing to transfer lease to [...] because
target may need a Raft snapshot: replica in StateProbe"
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blathers-crl bot commented May 25, 2023

Thanks for opening a backport.

Please check the backport criteria before merging:

  • Patches should only be created for serious issues or test-only changes.
  • Patches should not break backwards-compatibility.
  • Patches should change as little code as possible.
  • Patches should not change on-disk formats or node communication protocols.
  • Patches should not add new functionality.
  • Patches must not add, edit, or otherwise modify cluster versions; or add version gates.
If some of the basic criteria cannot be satisfied, ensure that the exceptional criteria are satisfied within.
  • There is a high priority need for the functionality that cannot wait until the next release and is difficult to address in another way.
  • The new functionality is additive-only and only runs for clusters which have specifically “opted in” to it (e.g. by a cluster setting).
  • New code is protected by a conditional check that is trivial to verify and ensures that it only runs for opt-in clusters.
  • The PM and TL on the team that owns the changed code have signed off that the change obeys the above rules.

Add a brief release justification to the body of your PR to justify this backport.

Some other things to consider:

  • What did we do to ensure that a user that doesn’t know & care about this backport, has no idea that it happened?
  • Will this work in a cluster of mixed patch versions? Did we test that?
  • If a user upgrades a patch version, uses this feature, and then downgrades, what happens?

@tbg tbg requested a review from erikgrinaker May 25, 2023 07:17
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This change is Reviewable

@tbg tbg marked this pull request as ready for review May 25, 2023 10:12
@tbg tbg requested a review from a team as a code owner May 25, 2023 10:12
@tbg tbg merged commit 4ce9320 into cockroachdb:release-22.2 May 25, 2023
@tbg tbg deleted the backport22.2-103827 branch May 25, 2023 10:12
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3 participants