kvserver: prevent StoreRebalancer from downreplicating #64650
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When the replication factor is lowered and the StoreRebalancer attempts a rebalance, it will accidentally perform a downreplication. Since it wasn't ever supposed to do that, the downreplication is pretty haphazard and doesn't safeguard quorum in the same way that a "proper" downreplication likely would. Prevent if from changing the number of voters and non-voters to avoid this issue. Annoyingly, I [knew] about this problem, but instead of fixing it at the source - as this commit does - I added a lower- level check that could then not be backported to release-20.2, where we are now seeing this problem. [knew]: cockroachdb#54444 (comment) Release note: None
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This change is |
nvanbenschoten
approved these changes
May 17, 2021
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bors r=erikgrinaker,nvanbenschoten I feel bad about merging this without a test but writing a test for this is a massive PITA, this fix is "obviously" working, and also I hear that @aayushshah15 has to rewrite this whole thing anyway. |
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bors r- |
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Canceled. |
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bors r=erikgrinaker,nvanbenschoten Just thought Aayush had discovered & fixed this independently, but he fixed another bug of the same sort: #64064 |
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Build succeeded: |
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When the replication factor is lowered and the StoreRebalancer
attempts a rebalance, it will accidentally perform a downreplication.
Since it wasn't ever supposed to do that, the downreplication is
pretty haphazard and doesn't safeguard quorum in the same way
that a "proper" downreplication likely would. Prevent if from
changing the number of voters and non-voters to avoid this issue.
Annoyingly, I knew about this problem, but instead of fixing it at the
source - as this commit does - I added a lower- level check that could
then not be backported to release-20.2, where we are now seeing this
problem.
#64649
Release note: None