docs(mem_wal): warn about stalled-writer race when WAL GC is added#6699
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Fencing relies on a stalled writer's put-if-not-exists colliding with the new writer's entry at the same WAL position. Once a future GC implementation deletes those entries, the stalled writer's PUT can land on empty space and silently acknowledge a write that will never be replayed. Document the hazard alongside the GC rules so implementations compensate (re-check fence on success, encode epoch in the filename, etc.). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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There is a corner case where GC can cleanup WAL log entries allowing a stalled writer (that has been fenced) to successfully acknowledge writes that are invalid. Since we do not have a GC process in OSS, because maintaining a long-running process isn't possible on the
ShardWriterhandle, this needs to be handled by whatever GC implementation is devised.