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storage: work around can't-swap-leaseholder #40363

Merged
merged 3 commits into from
Sep 3, 2019
Merged

storage: work around can't-swap-leaseholder #40363

merged 3 commits into from
Sep 3, 2019

Commits on Sep 3, 2019

  1. storage: remove errant log message 

    There may be nothing to roll back, so don't log unconditionally.

Release note: None
    @tbg
    tbg committed Sep 3, 2019
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  2. storage: make an error benign 

    This was showing up a lot in TestInitialPartitioning. If we're trying to
remove something but nothing needs to be removed, that seems OK (though
there is some question of why we're hitting this regularly).

Release note: None
    @tbg
    tbg committed Sep 3, 2019
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  3. storage: work around can't-swap-leaseholder 

    As of cockroachdb#40284, the replicate queue was issuing swaps (atomic add+remove)
during rebalancing.
TestInitialPartitioning helpfully points out (once you flip atomic
rebalancing on) that when the replication factor is one, there is
no way to perform such an atomic swap because it will necessarily
have to remove the leaseholder.

To work around this restriction (which, by the way, we dislike - see
\cockroachdb#40333), fall back to just adding a replica in this case without also
removing one. In the next scanner cycle (which should happen immediately
since we requeue the range) the range will be over-replicated and
hopefully the lease will be transferred over and then the original
leaseholder removed. I would be very doubtful that this all works,
but it is how things worked until cockroachdb#40284, so this PR really just
falls back to the previous behavior in cases where we can't do
better.

Release note: None
    @tbg
    tbg committed Sep 3, 2019
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