release-21.1: kvserver: prevent StoreRebalancer from downreplicating #65501
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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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erikgrinaker
approved these changes
May 20, 2021
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Backport 1/1 commits from #64650.
/cc @cockroachdb/release
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