Re: [I] [Bug] A Store rebuilt with an empty volume never rejoins its raft groups; retirement (Tombstone + patrol) cannot repair it and every health surface reads healthy [hugegraph]

["bitflicker64 (via GitHub)" <gi...@apache.org>]

bitflicker64 commented on issue #3227:
URL: https://github.com/apache/hugegraph/issues/3227#issuecomment-5795391573

   Diagram of the mechanism, and answers to the two questions from review: how rare the trigger is, and whether the fix is contained.
   
   ![PD writes the corrected shard list with the new id; the Store leader maps the unchanged raft address back to the old id through its stale local group and overwrites PD's record; no snapshot ever reaches the empty Store](https://raw.githubusercontent.com/bitflicker64/hugegraph/images/issue-3227/.github/images/issue-3227-overwrite-loop.svg)
   
   **Trigger.** The event is uncommon (a Store's data volume lost: disk failure, PVC deletion, node loss with local storage). The path is not: on Kubernetes a StatefulSet always rebuilds the pod at the same DNS raft address, so this is the default recovery route after any volume loss, and a bare-metal rebuild reusing host:port hits the same code. The multiplier is silence: nothing reports the lost replica, so the state persists until the next failure makes it two of three lost.
   
   **Fix shape.** Two bounded parts, no protocol change:
   
   1. Stop the overwrite: `getStoreByRaftEndpoint` falls back to PD's store list (preferring `Up`) when the id its local group holds for that address is no longer an active store. Small, `hg-store-core` only, fixes the bookkeeping.
   2. Make data flow: the group needs a real membership change so jraft installs a snapshot on the new id. Either PD drives remove-then-add when `reallocShards` swaps the id at an unchanged address, or the Store creates the missing partition engine when a conf notice names an address it serves with no engine. A few hundred lines in one module, depending on which layer owns it.
   
   Which layer do you prefer for part 2? I can build it and re-run the measured scenario from this report as the regression check.
   


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