Vladislav Shpilevoy
authored
swim_upsert_member is a function to add new members or update existing ones using info received from other cluster participants. At this moment it is quite simple and straightforward: either create a new member and return it, or update an existing member and return it. But things are going to change in failure detection and dissemination components. A couple of examples showing that a member should be returned separately from success/error status: * To prevent undead members the failure detection forbids to add dead members. Otherwise a dead member would be added and removed back and forth by different components infinitely. Upsert for such members should return NULL, but it is not an error - it is a normal function of the protocol; * When the dissemination component receives a UUID update of an existing member, but with too old incarnation, it does not apply that update. On the other hand it can not return that old member from upsert because of UUID being different from the one in the 'request'. In such a case it should be ok to return NULL, but do not deem it an error. Part of #3234
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