perf(service): Write HV tombstone before LT data to reduce orphan risk#365
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perf(service): Write HV tombstone before LT data to reduce orphan risk#365
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Previously, large-object inserts followed LT-first ordering: write data to long-term storage, then write the redirect tombstone to high-volume. A failure or pod kill between those two steps left an orphaned long-term object — data in LT with no tombstone in HV, permanently unreachable. This flips the ordering to HV-first: write the tombstone first, then write the data. A failure between the two steps now leaves a headless tombstone (tombstone in HV, no data in LT) instead. Headless tombstones are safe and self-healing: reads return None, deletes remove them, and re-inserts overwrite them. For small objects, a new `put_non_tombstone` trait method is added that atomically rejects the write if a tombstone already exists at the key, routing the payload to long-term storage instead. BigTable implements this with a CheckAndMutateRowRequest; other backends use a non-atomic read-then-write default. There is one remaining gap: a concurrent insert + delete can still race to produce an orphaned long-term object. Fixing that requires per-key serialization and is tracked separately. Co-Authored-By: Claude <noreply@anthropic.com>
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Deduplicates the expiration/mutation-building logic shared between put_row and put_non_tombstone into a single write_mutations method. Co-Authored-By: Claude <noreply@anthropic.com>
…tcome
Both types represented the same concept — an operation that either
executed or was blocked by a redirect tombstone — with different variant
names. Unify them into ConditionalOutcome { Executed, Tombstone }.
Co-Authored-By: Claude <noreply@anthropic.com>
…ibility Keep the ConditionalOutcome rename from this branch while adopting the pub visibility from main.
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Previously, large-object inserts followed LT-first ordering: write data to long-term storage, then write the redirect tombstone to high-volume. Concurrent inserts or pod kills between those two steps left an orphaned long-term object — data in LT with no tombstone in HV — permanently unreachable with no recovery path.
This flips the ordering to HV-first: write the tombstone first, then write the data. A failure between the two steps now produces a headless tombstone (tombstone in HV, no data in LT) instead. Headless tombstones are safe and self-healing: reads return
None, deletes remove them, and re-inserts overwrite them.The tradeoff is deliberate: we lower the risk of orphans in long-term storage — which are silent data leaks with no recovery — and instead accept headless tombstones, which are a well-defined recoverable state.
For small objects, a new
put_non_tombstonetrait method atomically rejects the write if a tombstone already exists at the key, routing the payload to long-term storage instead. BigTable implements this withCheckAndMutateRowRequest; other backends fall back to a non-atomic read-then-write.One gap remains: a concurrent insert + delete can still race to produce an orphaned long-term object. Fixing that requires per-key serialization. This PR is an intermediary improvement; the full solution with no orphans at all is tracked separately.
Ref FS-236