square/ttcache

ttcache's Issues

Concurrency Problems

An issue we haven't (knowingly) hit so far is what would happen if an update is successful but the cache clear isn't. See diagrams below:

So clearing after an update is potentially risky. Data might be updated while the cache still has stale data. What do you do in this case? Throw an exception? What if you don't?

If you clear the tag before the update, you risk the issue of a concurrent read.

A potential solution would be to run the updates as callbacks to clearTags and have clearTags start by setting a TTL on each of those tags.
If that fails, you throw and don't run the updates.
If that succeeds, you can run the updates, knowing that the system will return to consistency once the TTL is expired.