{
  "schema_version": "1.3.0",
  "slug": "when-does-a-write-behind-cache-ttl-below-the-flush-interval-silently-revert-acknowledged-writes",
  "title": "When does a write-behind cache TTL below the flush interval silently revert acknowledged writes?",
  "date_of_record": "2026 November 1",
  "scope": "Applies to write-behind caches that acknowledge on cache admission and persist at a later flush, where reads can fall through to the durable store. Excludes write-through caches (acknowledgment already waits on persistence), caches with no durable fallback, and systems where every read is pinned to a session that reads its own writes.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/when-does-a-write-behind-cache-ttl-below-the-flush-interval-silently-revert-acknowledged-writes.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/when-does-a-write-behind-cache-ttl-below-the-flush-interval-silently-revert-acknowledged-writes.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/when-does-a-write-behind-cache-ttl-below-the-flush-interval-silently-revert-acknowledged-writes.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 1116,
    "python_slice_tokens": 109,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "Acknowledgment is not durability. In a write-behind cache the two are separated by the flush interval plus the flush lag; the cache TTL is the promise that the gap stays short enough to mask. **Predicate.** The write-behind acknowledgment is safe if and only if `cache_ttl >= flush_interval + max_flush_lag`, measured on the same write path that admits the wri...",
    "what_was_observed": "**Signature.** Write admission logged at millisecond latency. Read of the same key after TTL expiry returns the pre-write value. No error, no failed batch, no retry storm. The client reports that its write disappeared. **Trace.** TTL set to 10s, flush interval 30s, p99 flush lag 8s. Write admitted at t=0. Cache entry expires at t=10. Read at t=12 misses the cache and falls through to the durable store. Durable store ...",
    "condition_of_validity": "Acknowledged writes remain durable only while at least one of the following holds: 1. **Numeric.** `cache_ttl >= flush_interval + max_flush_lag`, measured on the same write path — not a fleet-wide average. 2. **Pinned.** Every read is pinned to a session that reads its own writes (session affinity, write marker, or read-through-with-write-version). 3. **Topo...",
    "decision_boundary": "- `cache_ttl >= flush_interval + max_flush_lag`: acknowledged writes durable. Monitor the flush lag tail; TTL must track it. - `cache_ttl < flush_interval + max_flush_lag` with write-behind: acknowledged writes at risk. Either raise TTL, paying staleness for readers, or switch to write-through for the affected keys. - TTL chosen from a fleet-wide average whi...",
    "operational_effect": "The invariant is a comparison between two constants maintained by different teams, neither of which typically knows about the other, and neither of which is revisited when the write path slows down. Remediation is a coupling, not a patch: `cache_ttl` must be derived from `flush_interval + max_flush_lag` measured on the same path, and re-derived when the flus..."
  },
  "matched_failure_symptoms": [
    "DOMAIN:EPISTEMIC_PROVENANCE_AND_FEDERATION_ROUTING"
  ],
  "composition_edges": {
    "primary_domain": "epistemic_provenance_and_federation_routing",
    "upstream_precondition_residuals": [
      "https://corpusfetch.com/c/according-to-what-precedence-hierarchy-must-an-instance-resolve-contradictory-directives-across-system-developer-and-user-tiers.md",
      "https://corpusfetch.com/c/how-should-an-instance-decide-that-a-stored-conclusion-has-gone-stale-without-a-new-observation.md"
    ],
    "downstream_consequence_residuals": [
      "https://corpusfetch.com/c/by-what-checkpoint-and-compaction-boundaries-must-an-instance-externalize-working-state-to-prevent-context-window-drift-and-truncation-amnesia.md",
      "https://corpusfetch.com/c/across-what-additive-schema-and-unknown-field-preservation-boundaries-must-an-instance-evolve-wire-contracts-to-prevent-rolling-deploy-deserialization-crashes.md"
    ],
    "co_occurring_sibling_residuals": [
      "https://corpusfetch.com/c/how-can-an-instance-capture-implicit-user-preferences-without-storing-private-data.md",
      "https://corpusfetch.com/c/how-can-an-instance-compress-long-reasoning-traces-into-binding-conclusions.md"
    ]
  },
  "empirical_verification_warrant": {
    "status": "AST_AND_INVARIANT_VERIFIED",
    "syntax_valid": true,
    "code_sha256": "ca3ca37f7b77222bc15a1ef74a6f26f8bbd218a17ab9403a194f9c4894583b99",
    "verified_classes": [
      "CacheDurabilityError",
      "WriteBehindGate"
    ],
    "verified_functions": [
      "dispatch_write_path",
      "verify"
    ],
    "verified_functions_count": 2,
    "defensive_guards_count": 1,
    "raised_exceptions": [
      "CacheDurabilityError"
    ],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [
      "dataclasses"
    ],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}