Commits on May 12, 2021

1. kvserver: synchronize replica removal with read-write requests …

   Replica removal did not synchronize with in-flight read-write requests,
   which could cause them to be evaluated on a removed (empty) replica. The
   request would not be able to persist any writes, since it's unable to
   submit Raft proposals. However, it can affect conditional writes, for
   example causing a `ConditionalPutRequest` to error because it finds a
   missing value instead of the expected one.
   
   This patch fixes the problem by taking out `Replica.readOnlyCmdMu`
   during pre-Raft evaluation, to synchronize with replica removal. This
   can cause such requests to return `AmbiguousResultError` as the write is
   evaluated.
   
   Release note (bug fix): Fixed a race condition where read-write requests
   during replica removal (e.g. during range merges or rebalancing) could
   be evaluated on the removed replica. These will not have been able to
   write any data to persistent storage, but could behave unexpectedly,
   e.g. returning errors that they should not have returned.

   

   erikgrinaker committed May 12, 2021
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