4 ms·

iam is eventually consistent...because its caching so much. we can see changes easily take a minute to propagate

• bastawhiz 5y ago
  Replication delay and stale caches are two different problems with vastly different causes
  • josephh 5y ago
    Can you elaborate more? Is it not possible to have replication delay due to stale caches?
    • bastawhiz 5y ago
      I'm not aware of a data store which populates its replicas with data from a cache. Surely there are caches within any given data store, but the whole point of a replica is to have the data replicated (for scaling reads, redundancy in case your leader fails). If you're using caches, you're deliberately sending old data to the replicas. I can't think of why you'd do that. I guess you could have replicas of your caches, but I'm referring specifically to data store replicas.
  • nicoburns 5y ago
    Is a replica not a cache of sorts?
    • bastawhiz 5y ago
      Not really. Replicas are constantly replicating live data from your leader. All of it, in its raw form. A query against a replica isn't inherently faster than a query against the leader, the data is likely just a bit old. A cache stores the output of an operation to avoid needing to perform the same operation again. You deliberately put data into a cache to avoid needing to create that data a second time—it won't magically appear there.