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Incorrect ViewChange messages consensus calculating #1506

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Toktar opened this issue Jan 22, 2021 · 1 comment
Open

Incorrect ViewChange messages consensus calculating #1506

Toktar opened this issue Jan 22, 2021 · 1 comment

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@Toktar
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Toktar commented Jan 22, 2021

The simulation test for ViewChange sometimes fails

def test_new_view_combinations(random):

because of problem with getting a checkpoint on the phase of collecting ViewChange messages in the method calc_checkpoint(). It receives a list of ViewChange messages like a parameter.
If it's a 4 node pool and the list contains the follow ViewChange messages

  • ViewChange_1 | checkpoints_ends: 10, 20 | stable_checkpoint: 10
  • ViewChange_2 | checkpoints_ends: 0, 10 | stable_checkpoint: 0
  • ViewChange_2 | checkpoints_ends: 0 | stable_checkpoint: 0

Then we don't have a strong consensus of 3 (n-f=4-1) checkpoins with the same checkpoint end. It means, that the node can't finish a view change.

Expected problem: Low probability one or more nodes may not finish View Change and after a short period just start a new one.
With an incredibly low probability a pool can freeze with endless view changes. But it can be fixed by POOL_RESTART transaction.

We don’t think we have a big chance to face this case. But we need to remember about it and fix.

@Toktar Toktar changed the title ViewChange consensus protocol problem Incorrect ViewChange messages consensus calculating Jan 22, 2021
Toktar pushed a commit to Toktar/indy-plenum that referenced this issue Feb 26, 2021
…r#1506

Signed-off-by: toktar <renata.toktar@evernym.com>
Toktar pushed a commit to Toktar/indy-plenum that referenced this issue Mar 1, 2021
…r#1506

Signed-off-by: toktar <renata.toktar@evernym.com>
Toktar pushed a commit to Toktar/indy-plenum that referenced this issue Mar 1, 2021
…r#1506

Signed-off-by: toktar <renata.toktar@evernym.com>
Toktar pushed a commit to Toktar/indy-plenum that referenced this issue Mar 15, 2021
…r#1506

Signed-off-by: toktar <renata.toktar@evernym.com>
Toktar pushed a commit to Toktar/indy-plenum that referenced this issue Mar 24, 2021
@WadeBarnes
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WadeBarnes commented Mar 24, 2021

When addressing this issue, please ensure any workarounds such as this are addressed;

cp = pool.nodes[0]._view_changer._new_view_builder.calc_checkpoint(votes)
# In some cases checkpoints can't be collected. Uncomment this after fixing issue #1506
# assert cp is not None

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