Avoid fast past update restart race with concurrently created replica #11561
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After the recent change to allow safe path updates to be restarted as fast path updates iff all observed document timestamps are equal, a race condition regression was introduced. If the bucket that the update operation was scheduled towards got a new replica concurrently created _between_ the time that safe path Gets were sent and received, it was possible for updates to be sent to inconsistent replicas. This is because the Get and Update operations use the current database state at _their_ start time, not a stable snapshot state from the start time of the two phase update operation itself. Add an explicit check that the replica state between sending Gets and Updates is unchanged. If it has changed, a fast path restart is _not_ permitted.
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Even with the fix in #11561 we are still observing replica divergence warnings in the logs. Disabling this feature entirely until the issue has been fully investigated and a complete fix has been implemented. Also emit a log message when the distributor has forced convergence of a detected inconsistent update.
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Even with the fix in #11561 we are still observing replica divergence warnings in the logs. Disabling this feature entirely until the issue has been fully investigated and a complete fix has been implemented. Also emit a log message when the distributor has forced convergence of a detected inconsistent update.
This was referenced Dec 20, 2019
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@geirst please review. This fix was hammered out in a cramped seat at 35,000 feet (occasionally interrupted by a high fidelity surround sound setup of screaming infants) so I will likely polish these changes a bit later...!
After the recent change to allow safe path updates to be restarted
as fast path updates iff all observed document timestamps are equal,
a race condition regression was introduced. If the bucket that the
update operation was scheduled towards got a new replica concurrently
created between the time that safe path Gets were sent and received,
it was possible for updates to be sent to inconsistent replicas. This
is because the Get and Update operations use the current database
state at their start time, not a stable snapshot state from the start
time of the two phase update operation itself.
Add an explicit check that the replica state between sending Gets and
Updates is unchanged. If it has changed, a fast path restart is not
permitted.