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// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
#pragma once
#include <vespa/vespalib/util/time.h>
namespace storage::distributor {
/**
* When bucket ownership changes in a cluster, there exists a time period
* where distributors, unless prevented to do so, may generate the same time
* stamps as previous distributors. This may cause time stamp collisions
* within buckets, which we do not have a good story for today.
*
* An ownership transfer waiter is a stop-gap solution to avoiding this
* edge case. It assumes that, given a maximum expected clock skew in the
* cluster, it is sufficient to wait until the (ceil(current time) + max skew)
* time point has elapsed. Until this time point is reached, mutating external
* feed operations that require timestamps will be bounced back to the client.
*
* This is a stop-gap solution in the sense that we later want to move to a
* solution which is _aware_ of the maximum time stamp for any bucket owned
* by this distributor and refuse to generate any operation with a time stamp
* equal to or lower than this. The stop-gap also breaks down if, in fact,
* the clock skew is higher than the expected one.
*
*/
class OwnershipTransferSafeTimePointCalculator {
std::chrono::seconds _max_cluster_clock_skew;
public:
explicit OwnershipTransferSafeTimePointCalculator(std::chrono::seconds max_cluster_clock_skew)
: _max_cluster_clock_skew(max_cluster_clock_skew)
{
}
void setMaxClusterClockSkew(std::chrono::seconds sec) noexcept {
_max_cluster_clock_skew = sec;
}
vespalib::system_time safeTimePoint(vespalib::system_time now) const;
};
}
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