Edge Cache and CDN Platform · View 16 of 29 · 5 · Runtime
Why nothing is deleted
- Enumerating two million objects on 90 nodes is 180 million deletes, with index scans on every node, during the minutes a release most needs the serving path. Instead the node records one row: tag price-list, invalidated at 19:00:02.114.
- Every stored object carries its tags and its store time. On lookup, if any of its tags was invalidated after it was stored, the object is a miss (purge) or stale (expire). The cost of a purge no longer depends on how many objects it matches.
- The table stays small because entries only need to outlive the longest TTL. The 30-day TTL ceiling therefore also bounds the size of the tag table.
What acknowledged means
- A PoP acknowledges after every node's tag table has committed the record, not when the message arrives. The ledger records which sequence number each PoP has applied up to.
Numbers
- R3 quorum write across three sites about 200 ms; mirror to the farthest PoP about 300 ms; apply and acknowledge under 100 ms. Typically under 2 s end to end against a 5 s p95 budget.
